Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Matthias J. Sax]

Ah thanks. I did not check the wiki but just browsed through all open
KIP discussions following the email threads.


-Matthias

On 9/30/18 12:06 PM, Dong Lin wrote:
> Hey Matthias,
> 
> Thanks for checking back  on the status. The KIP has been marked as
> replaced by KIP-320 in the KIP list wiki page and the status has been
> updated in the discussion and voting email thread.
> 
> Thanks,
> Dong
> 
> On Sun, 30 Sep 2018 at 11:51 AM Matthias J. Sax 
> wrote:
> 
>> It seems that KIP-320 was accepted. Thus, I am wondering what the status
>> of this KIP is?
>>
>> -Matthias
>>
>> On 7/11/18 10:59 AM, Dong Lin wrote:
>>> Hey Jun,
>>>
>>> Certainly. We can discuss later after KIP-320 settles.
>>>
>>> Thanks!
>>> Dong
>>>
>>>
>>> On Wed, Jul 11, 2018 at 8:54 AM, Jun Rao  wrote:
>>>
 Hi, Dong,

 Sorry for the late response. Since KIP-320 is covering some of the
>> similar
 problems described in this KIP, perhaps we can wait until KIP-320
>> settles
 and see what's still left uncovered in this KIP.

 Thanks,

 Jun

 On Mon, Jun 4, 2018 at 7:03 PM, Dong Lin  wrote:

> Hey Jun,
>
> It seems that we have made considerable progress on the discussion of
> KIP-253 since February. Do you think we should continue the discussion
> there, or can we continue the voting for this KIP? I am happy to submit
 the
> PR and move forward the progress for this KIP.
>
> Thanks!
> Dong
>
>
> On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:
>
>> Hey Jun,
>>
>> Sure, I will come up with a KIP this week. I think there is a way to
> allow
>> partition expansion to arbitrary number without introducing new
 concepts
>> such as read-only partition or repartition epoch.
>>
>> Thanks,
>> Dong
>>
>> On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:
>>
>>> Hi, Dong,
>>>
>>> Thanks for the reply. The general idea that you had for adding
> partitions
>>> is similar to what we had in mind. It would be useful to make this
 more
>>> general, allowing adding an arbitrary number of partitions (instead
>> of
>>> just
>>> doubling) and potentially removing partitions as well. The following
 is
>>> the
>>> high level idea from the discussion with Colin, Jason and Ismael.
>>>
>>> * To change the number of partitions from X to Y in a topic, the
>>> controller
>>> marks all existing X partitions as read-only and creates Y new
> partitions.
>>> The new partitions are writable and are tagged with a higher
 repartition
>>> epoch (RE).
>>>
>>> * The controller propagates the new metadata to every broker. Once
>> the
>>> leader of a partition is marked as read-only, it rejects the produce
>>> requests on this partition. The producer will then refresh the
 metadata
>>> and
>>> start publishing to the new writable partitions.
>>>
>>> * The consumers will then be consuming messages in RE order. The
> consumer
>>> coordinator will only assign partitions in the same RE to consumers.
> Only
>>> after all messages in an RE are consumed, will partitions in a higher
 RE
>>> be
>>> assigned to consumers.
>>>
>>> As Colin mentioned, if we do the above, we could potentially (1) use
>> a
>>> globally unique partition id, or (2) use a globally unique topic id
>> to
>>> distinguish recreated partitions due to topic deletion.
>>>
>>> So, perhaps we can sketch out the re-partitioning KIP a bit more and
 see
>>> if
>>> there is any overlap with KIP-232. Would you be interested in doing
> that?
>>> If not, we can do that next week.
>>>
>>> Jun
>>>
>>>
>>> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin 
 wrote:
>>>
 Hey Jun,

 Interestingly I am also planning to sketch a KIP to allow partition
 expansion for keyed topics after this KIP. Since you are already
 doing
 that, I guess I will just share my high level idea here in case it
 is
 helpful.

 The motivation for the KIP is that we currently lose order guarantee
> for
 messages with the same key if we expand partitions of keyed topic.

 The solution can probably be built upon the following ideas:

 - Partition number of the keyed topic should always be doubled (or
 multiplied by power of 2). Given that we select a partition based on
 hash(key) % partitionNum, this should help us ensure that, a message
 assigned to an existing partition will not be mapped to another
> existing
 partition after partition expansion.

 - Producer includes in the ProduceRequest some information that
 helps
 ensure that messages produced ti a partition will monotonically
>>> increase in
 the partitionNum of 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Matthias,

Thanks for checking back  on the status. The KIP has been marked as
replaced by KIP-320 in the KIP list wiki page and the status has been
updated in the discussion and voting email thread.

Thanks,
Dong

On Sun, 30 Sep 2018 at 11:51 AM Matthias J. Sax 
wrote:

> It seems that KIP-320 was accepted. Thus, I am wondering what the status
> of this KIP is?
>
> -Matthias
>
> On 7/11/18 10:59 AM, Dong Lin wrote:
> > Hey Jun,
> >
> > Certainly. We can discuss later after KIP-320 settles.
> >
> > Thanks!
> > Dong
> >
> >
> > On Wed, Jul 11, 2018 at 8:54 AM, Jun Rao  wrote:
> >
> >> Hi, Dong,
> >>
> >> Sorry for the late response. Since KIP-320 is covering some of the
> similar
> >> problems described in this KIP, perhaps we can wait until KIP-320
> settles
> >> and see what's still left uncovered in this KIP.
> >>
> >> Thanks,
> >>
> >> Jun
> >>
> >> On Mon, Jun 4, 2018 at 7:03 PM, Dong Lin  wrote:
> >>
> >>> Hey Jun,
> >>>
> >>> It seems that we have made considerable progress on the discussion of
> >>> KIP-253 since February. Do you think we should continue the discussion
> >>> there, or can we continue the voting for this KIP? I am happy to submit
> >> the
> >>> PR and move forward the progress for this KIP.
> >>>
> >>> Thanks!
> >>> Dong
> >>>
> >>>
> >>> On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:
> >>>
>  Hey Jun,
> 
>  Sure, I will come up with a KIP this week. I think there is a way to
> >>> allow
>  partition expansion to arbitrary number without introducing new
> >> concepts
>  such as read-only partition or repartition epoch.
> 
>  Thanks,
>  Dong
> 
>  On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:
> 
> > Hi, Dong,
> >
> > Thanks for the reply. The general idea that you had for adding
> >>> partitions
> > is similar to what we had in mind. It would be useful to make this
> >> more
> > general, allowing adding an arbitrary number of partitions (instead
> of
> > just
> > doubling) and potentially removing partitions as well. The following
> >> is
> > the
> > high level idea from the discussion with Colin, Jason and Ismael.
> >
> > * To change the number of partitions from X to Y in a topic, the
> > controller
> > marks all existing X partitions as read-only and creates Y new
> >>> partitions.
> > The new partitions are writable and are tagged with a higher
> >> repartition
> > epoch (RE).
> >
> > * The controller propagates the new metadata to every broker. Once
> the
> > leader of a partition is marked as read-only, it rejects the produce
> > requests on this partition. The producer will then refresh the
> >> metadata
> > and
> > start publishing to the new writable partitions.
> >
> > * The consumers will then be consuming messages in RE order. The
> >>> consumer
> > coordinator will only assign partitions in the same RE to consumers.
> >>> Only
> > after all messages in an RE are consumed, will partitions in a higher
> >> RE
> > be
> > assigned to consumers.
> >
> > As Colin mentioned, if we do the above, we could potentially (1) use
> a
> > globally unique partition id, or (2) use a globally unique topic id
> to
> > distinguish recreated partitions due to topic deletion.
> >
> > So, perhaps we can sketch out the re-partitioning KIP a bit more and
> >> see
> > if
> > there is any overlap with KIP-232. Would you be interested in doing
> >>> that?
> > If not, we can do that next week.
> >
> > Jun
> >
> >
> > On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin 
> >> wrote:
> >
> >> Hey Jun,
> >>
> >> Interestingly I am also planning to sketch a KIP to allow partition
> >> expansion for keyed topics after this KIP. Since you are already
> >> doing
> >> that, I guess I will just share my high level idea here in case it
> >> is
> >> helpful.
> >>
> >> The motivation for the KIP is that we currently lose order guarantee
> >>> for
> >> messages with the same key if we expand partitions of keyed topic.
> >>
> >> The solution can probably be built upon the following ideas:
> >>
> >> - Partition number of the keyed topic should always be doubled (or
> >> multiplied by power of 2). Given that we select a partition based on
> >> hash(key) % partitionNum, this should help us ensure that, a message
> >> assigned to an existing partition will not be mapped to another
> >>> existing
> >> partition after partition expansion.
> >>
> >> - Producer includes in the ProduceRequest some information that
> >> helps
> >> ensure that messages produced ti a partition will monotonically
> > increase in
> >> the partitionNum of the topic. In other words, if broker receives a
> >> ProduceRequest and notices that the producer does not know the
> >>> partition
> >> number has increased, broker should reject this 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Matthias J. Sax]

It seems that KIP-320 was accepted. Thus, I am wondering what the status
of this KIP is?

-Matthias

On 7/11/18 10:59 AM, Dong Lin wrote:
> Hey Jun,
> 
> Certainly. We can discuss later after KIP-320 settles.
> 
> Thanks!
> Dong
> 
> 
> On Wed, Jul 11, 2018 at 8:54 AM, Jun Rao  wrote:
> 
>> Hi, Dong,
>>
>> Sorry for the late response. Since KIP-320 is covering some of the similar
>> problems described in this KIP, perhaps we can wait until KIP-320 settles
>> and see what's still left uncovered in this KIP.
>>
>> Thanks,
>>
>> Jun
>>
>> On Mon, Jun 4, 2018 at 7:03 PM, Dong Lin  wrote:
>>
>>> Hey Jun,
>>>
>>> It seems that we have made considerable progress on the discussion of
>>> KIP-253 since February. Do you think we should continue the discussion
>>> there, or can we continue the voting for this KIP? I am happy to submit
>> the
>>> PR and move forward the progress for this KIP.
>>>
>>> Thanks!
>>> Dong
>>>
>>>
>>> On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:
>>>
 Hey Jun,

 Sure, I will come up with a KIP this week. I think there is a way to
>>> allow
 partition expansion to arbitrary number without introducing new
>> concepts
 such as read-only partition or repartition epoch.

 Thanks,
 Dong

 On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:

> Hi, Dong,
>
> Thanks for the reply. The general idea that you had for adding
>>> partitions
> is similar to what we had in mind. It would be useful to make this
>> more
> general, allowing adding an arbitrary number of partitions (instead of
> just
> doubling) and potentially removing partitions as well. The following
>> is
> the
> high level idea from the discussion with Colin, Jason and Ismael.
>
> * To change the number of partitions from X to Y in a topic, the
> controller
> marks all existing X partitions as read-only and creates Y new
>>> partitions.
> The new partitions are writable and are tagged with a higher
>> repartition
> epoch (RE).
>
> * The controller propagates the new metadata to every broker. Once the
> leader of a partition is marked as read-only, it rejects the produce
> requests on this partition. The producer will then refresh the
>> metadata
> and
> start publishing to the new writable partitions.
>
> * The consumers will then be consuming messages in RE order. The
>>> consumer
> coordinator will only assign partitions in the same RE to consumers.
>>> Only
> after all messages in an RE are consumed, will partitions in a higher
>> RE
> be
> assigned to consumers.
>
> As Colin mentioned, if we do the above, we could potentially (1) use a
> globally unique partition id, or (2) use a globally unique topic id to
> distinguish recreated partitions due to topic deletion.
>
> So, perhaps we can sketch out the re-partitioning KIP a bit more and
>> see
> if
> there is any overlap with KIP-232. Would you be interested in doing
>>> that?
> If not, we can do that next week.
>
> Jun
>
>
> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin 
>> wrote:
>
>> Hey Jun,
>>
>> Interestingly I am also planning to sketch a KIP to allow partition
>> expansion for keyed topics after this KIP. Since you are already
>> doing
>> that, I guess I will just share my high level idea here in case it
>> is
>> helpful.
>>
>> The motivation for the KIP is that we currently lose order guarantee
>>> for
>> messages with the same key if we expand partitions of keyed topic.
>>
>> The solution can probably be built upon the following ideas:
>>
>> - Partition number of the keyed topic should always be doubled (or
>> multiplied by power of 2). Given that we select a partition based on
>> hash(key) % partitionNum, this should help us ensure that, a message
>> assigned to an existing partition will not be mapped to another
>>> existing
>> partition after partition expansion.
>>
>> - Producer includes in the ProduceRequest some information that
>> helps
>> ensure that messages produced ti a partition will monotonically
> increase in
>> the partitionNum of the topic. In other words, if broker receives a
>> ProduceRequest and notices that the producer does not know the
>>> partition
>> number has increased, broker should reject this request. That
> "information"
>> maybe leaderEpoch, max partitionEpoch of the partitions of the
>> topic,
>>> or
>> simply partitionNum of the topic. The benefit of this property is
>> that
> we
>> can keep the new logic for in-order message consumption entirely in
>>> how
>> consumer leader determines the partition -> consumer mapping.
>>
>> - When consumer leader determines partition -> consumer mapping,
>>> leader
>> first reads the start position for each partition using
> OffsetFetchRequest.
>> If start position 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

For record purpose, this KIP is closed as its design has been merged into
KIP-320. See
https://cwiki.apache.org/confluence/display/KAFKA/KIP-320%3A+Allow+fetchers+to+detect+and+handle+log+truncation
.

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Jun,

Certainly. We can discuss later after KIP-320 settles.

Thanks!
Dong


On Wed, Jul 11, 2018 at 8:54 AM, Jun Rao  wrote:

> Hi, Dong,
>
> Sorry for the late response. Since KIP-320 is covering some of the similar
> problems described in this KIP, perhaps we can wait until KIP-320 settles
> and see what's still left uncovered in this KIP.
>
> Thanks,
>
> Jun
>
> On Mon, Jun 4, 2018 at 7:03 PM, Dong Lin  wrote:
>
> > Hey Jun,
> >
> > It seems that we have made considerable progress on the discussion of
> > KIP-253 since February. Do you think we should continue the discussion
> > there, or can we continue the voting for this KIP? I am happy to submit
> the
> > PR and move forward the progress for this KIP.
> >
> > Thanks!
> > Dong
> >
> >
> > On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:
> >
> > > Hey Jun,
> > >
> > > Sure, I will come up with a KIP this week. I think there is a way to
> > allow
> > > partition expansion to arbitrary number without introducing new
> concepts
> > > such as read-only partition or repartition epoch.
> > >
> > > Thanks,
> > > Dong
> > >
> > > On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:
> > >
> > >> Hi, Dong,
> > >>
> > >> Thanks for the reply. The general idea that you had for adding
> > partitions
> > >> is similar to what we had in mind. It would be useful to make this
> more
> > >> general, allowing adding an arbitrary number of partitions (instead of
> > >> just
> > >> doubling) and potentially removing partitions as well. The following
> is
> > >> the
> > >> high level idea from the discussion with Colin, Jason and Ismael.
> > >>
> > >> * To change the number of partitions from X to Y in a topic, the
> > >> controller
> > >> marks all existing X partitions as read-only and creates Y new
> > partitions.
> > >> The new partitions are writable and are tagged with a higher
> repartition
> > >> epoch (RE).
> > >>
> > >> * The controller propagates the new metadata to every broker. Once the
> > >> leader of a partition is marked as read-only, it rejects the produce
> > >> requests on this partition. The producer will then refresh the
> metadata
> > >> and
> > >> start publishing to the new writable partitions.
> > >>
> > >> * The consumers will then be consuming messages in RE order. The
> > consumer
> > >> coordinator will only assign partitions in the same RE to consumers.
> > Only
> > >> after all messages in an RE are consumed, will partitions in a higher
> RE
> > >> be
> > >> assigned to consumers.
> > >>
> > >> As Colin mentioned, if we do the above, we could potentially (1) use a
> > >> globally unique partition id, or (2) use a globally unique topic id to
> > >> distinguish recreated partitions due to topic deletion.
> > >>
> > >> So, perhaps we can sketch out the re-partitioning KIP a bit more and
> see
> > >> if
> > >> there is any overlap with KIP-232. Would you be interested in doing
> > that?
> > >> If not, we can do that next week.
> > >>
> > >> Jun
> > >>
> > >>
> > >> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin 
> wrote:
> > >>
> > >> > Hey Jun,
> > >> >
> > >> > Interestingly I am also planning to sketch a KIP to allow partition
> > >> > expansion for keyed topics after this KIP. Since you are already
> doing
> > >> > that, I guess I will just share my high level idea here in case it
> is
> > >> > helpful.
> > >> >
> > >> > The motivation for the KIP is that we currently lose order guarantee
> > for
> > >> > messages with the same key if we expand partitions of keyed topic.
> > >> >
> > >> > The solution can probably be built upon the following ideas:
> > >> >
> > >> > - Partition number of the keyed topic should always be doubled (or
> > >> > multiplied by power of 2). Given that we select a partition based on
> > >> > hash(key) % partitionNum, this should help us ensure that, a message
> > >> > assigned to an existing partition will not be mapped to another
> > existing
> > >> > partition after partition expansion.
> > >> >
> > >> > - Producer includes in the ProduceRequest some information that
> helps
> > >> > ensure that messages produced ti a partition will monotonically
> > >> increase in
> > >> > the partitionNum of the topic. In other words, if broker receives a
> > >> > ProduceRequest and notices that the producer does not know the
> > partition
> > >> > number has increased, broker should reject this request. That
> > >> "information"
> > >> > maybe leaderEpoch, max partitionEpoch of the partitions of the
> topic,
> > or
> > >> > simply partitionNum of the topic. The benefit of this property is
> that
> > >> we
> > >> > can keep the new logic for in-order message consumption entirely in
> > how
> > >> > consumer leader determines the partition -> consumer mapping.
> > >> >
> > >> > - When consumer leader determines partition -> consumer mapping,
> > leader
> > >> > first reads the start position for each partition using
> > >> OffsetFetchRequest.
> > >> > If start position are all non-zero, then assignment can be done in
> its
> > >> > 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Jun Rao]

Hi, Dong,

Sorry for the late response. Since KIP-320 is covering some of the similar
problems described in this KIP, perhaps we can wait until KIP-320 settles
and see what's still left uncovered in this KIP.

Thanks,

Jun

On Mon, Jun 4, 2018 at 7:03 PM, Dong Lin  wrote:

> Hey Jun,
>
> It seems that we have made considerable progress on the discussion of
> KIP-253 since February. Do you think we should continue the discussion
> there, or can we continue the voting for this KIP? I am happy to submit the
> PR and move forward the progress for this KIP.
>
> Thanks!
> Dong
>
>
> On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:
>
> > Hey Jun,
> >
> > Sure, I will come up with a KIP this week. I think there is a way to
> allow
> > partition expansion to arbitrary number without introducing new concepts
> > such as read-only partition or repartition epoch.
> >
> > Thanks,
> > Dong
> >
> > On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:
> >
> >> Hi, Dong,
> >>
> >> Thanks for the reply. The general idea that you had for adding
> partitions
> >> is similar to what we had in mind. It would be useful to make this more
> >> general, allowing adding an arbitrary number of partitions (instead of
> >> just
> >> doubling) and potentially removing partitions as well. The following is
> >> the
> >> high level idea from the discussion with Colin, Jason and Ismael.
> >>
> >> * To change the number of partitions from X to Y in a topic, the
> >> controller
> >> marks all existing X partitions as read-only and creates Y new
> partitions.
> >> The new partitions are writable and are tagged with a higher repartition
> >> epoch (RE).
> >>
> >> * The controller propagates the new metadata to every broker. Once the
> >> leader of a partition is marked as read-only, it rejects the produce
> >> requests on this partition. The producer will then refresh the metadata
> >> and
> >> start publishing to the new writable partitions.
> >>
> >> * The consumers will then be consuming messages in RE order. The
> consumer
> >> coordinator will only assign partitions in the same RE to consumers.
> Only
> >> after all messages in an RE are consumed, will partitions in a higher RE
> >> be
> >> assigned to consumers.
> >>
> >> As Colin mentioned, if we do the above, we could potentially (1) use a
> >> globally unique partition id, or (2) use a globally unique topic id to
> >> distinguish recreated partitions due to topic deletion.
> >>
> >> So, perhaps we can sketch out the re-partitioning KIP a bit more and see
> >> if
> >> there is any overlap with KIP-232. Would you be interested in doing
> that?
> >> If not, we can do that next week.
> >>
> >> Jun
> >>
> >>
> >> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin  wrote:
> >>
> >> > Hey Jun,
> >> >
> >> > Interestingly I am also planning to sketch a KIP to allow partition
> >> > expansion for keyed topics after this KIP. Since you are already doing
> >> > that, I guess I will just share my high level idea here in case it is
> >> > helpful.
> >> >
> >> > The motivation for the KIP is that we currently lose order guarantee
> for
> >> > messages with the same key if we expand partitions of keyed topic.
> >> >
> >> > The solution can probably be built upon the following ideas:
> >> >
> >> > - Partition number of the keyed topic should always be doubled (or
> >> > multiplied by power of 2). Given that we select a partition based on
> >> > hash(key) % partitionNum, this should help us ensure that, a message
> >> > assigned to an existing partition will not be mapped to another
> existing
> >> > partition after partition expansion.
> >> >
> >> > - Producer includes in the ProduceRequest some information that helps
> >> > ensure that messages produced ti a partition will monotonically
> >> increase in
> >> > the partitionNum of the topic. In other words, if broker receives a
> >> > ProduceRequest and notices that the producer does not know the
> partition
> >> > number has increased, broker should reject this request. That
> >> "information"
> >> > maybe leaderEpoch, max partitionEpoch of the partitions of the topic,
> or
> >> > simply partitionNum of the topic. The benefit of this property is that
> >> we
> >> > can keep the new logic for in-order message consumption entirely in
> how
> >> > consumer leader determines the partition -> consumer mapping.
> >> >
> >> > - When consumer leader determines partition -> consumer mapping,
> leader
> >> > first reads the start position for each partition using
> >> OffsetFetchRequest.
> >> > If start position are all non-zero, then assignment can be done in its
> >> > current manner. The assumption is that, a message in the new partition
> >> > should only be consumed after all messages with the same key produced
> >> > before it has been consumed. Since some messages in the new partition
> >> has
> >> > been consumed, we should not worry about consuming messages
> >> out-of-order.
> >> > This benefit of this approach is that we can avoid unnecessary
> overhead
> >> in

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Jun,

It seems that we have made considerable progress on the discussion of
KIP-253 since February. Do you think we should continue the discussion
there, or can we continue the voting for this KIP? I am happy to submit the
PR and move forward the progress for this KIP.

Thanks!
Dong


On Wed, Feb 7, 2018 at 11:42 PM, Dong Lin  wrote:

> Hey Jun,
>
> Sure, I will come up with a KIP this week. I think there is a way to allow
> partition expansion to arbitrary number without introducing new concepts
> such as read-only partition or repartition epoch.
>
> Thanks,
> Dong
>
> On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:
>
>> Hi, Dong,
>>
>> Thanks for the reply. The general idea that you had for adding partitions
>> is similar to what we had in mind. It would be useful to make this more
>> general, allowing adding an arbitrary number of partitions (instead of
>> just
>> doubling) and potentially removing partitions as well. The following is
>> the
>> high level idea from the discussion with Colin, Jason and Ismael.
>>
>> * To change the number of partitions from X to Y in a topic, the
>> controller
>> marks all existing X partitions as read-only and creates Y new partitions.
>> The new partitions are writable and are tagged with a higher repartition
>> epoch (RE).
>>
>> * The controller propagates the new metadata to every broker. Once the
>> leader of a partition is marked as read-only, it rejects the produce
>> requests on this partition. The producer will then refresh the metadata
>> and
>> start publishing to the new writable partitions.
>>
>> * The consumers will then be consuming messages in RE order. The consumer
>> coordinator will only assign partitions in the same RE to consumers. Only
>> after all messages in an RE are consumed, will partitions in a higher RE
>> be
>> assigned to consumers.
>>
>> As Colin mentioned, if we do the above, we could potentially (1) use a
>> globally unique partition id, or (2) use a globally unique topic id to
>> distinguish recreated partitions due to topic deletion.
>>
>> So, perhaps we can sketch out the re-partitioning KIP a bit more and see
>> if
>> there is any overlap with KIP-232. Would you be interested in doing that?
>> If not, we can do that next week.
>>
>> Jun
>>
>>
>> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin  wrote:
>>
>> > Hey Jun,
>> >
>> > Interestingly I am also planning to sketch a KIP to allow partition
>> > expansion for keyed topics after this KIP. Since you are already doing
>> > that, I guess I will just share my high level idea here in case it is
>> > helpful.
>> >
>> > The motivation for the KIP is that we currently lose order guarantee for
>> > messages with the same key if we expand partitions of keyed topic.
>> >
>> > The solution can probably be built upon the following ideas:
>> >
>> > - Partition number of the keyed topic should always be doubled (or
>> > multiplied by power of 2). Given that we select a partition based on
>> > hash(key) % partitionNum, this should help us ensure that, a message
>> > assigned to an existing partition will not be mapped to another existing
>> > partition after partition expansion.
>> >
>> > - Producer includes in the ProduceRequest some information that helps
>> > ensure that messages produced ti a partition will monotonically
>> increase in
>> > the partitionNum of the topic. In other words, if broker receives a
>> > ProduceRequest and notices that the producer does not know the partition
>> > number has increased, broker should reject this request. That
>> "information"
>> > maybe leaderEpoch, max partitionEpoch of the partitions of the topic, or
>> > simply partitionNum of the topic. The benefit of this property is that
>> we
>> > can keep the new logic for in-order message consumption entirely in how
>> > consumer leader determines the partition -> consumer mapping.
>> >
>> > - When consumer leader determines partition -> consumer mapping, leader
>> > first reads the start position for each partition using
>> OffsetFetchRequest.
>> > If start position are all non-zero, then assignment can be done in its
>> > current manner. The assumption is that, a message in the new partition
>> > should only be consumed after all messages with the same key produced
>> > before it has been consumed. Since some messages in the new partition
>> has
>> > been consumed, we should not worry about consuming messages
>> out-of-order.
>> > This benefit of this approach is that we can avoid unnecessary overhead
>> in
>> > the common case.
>> >
>> > - If the consumer leader finds that the start position for some
>> partition
>> > is 0. Say the current partition number is 18 and the partition index is
>> 12,
>> > then consumer leader should ensure that messages produced to partition
>> 12 -
>> > 18/2 = 3 before the first message of partition 12 is consumed, before it
>> > assigned partition 12 to any consumer in the consumer group. Since we
>> have
>> > a "information" that is monotonically increasing per partition, 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Jun,

Sure, I will come up with a KIP this week. I think there is a way to allow
partition expansion to arbitrary number without introducing new concepts
such as read-only partition or repartition epoch.

Thanks,
Dong

On Wed, Feb 7, 2018 at 5:28 PM, Jun Rao  wrote:

> Hi, Dong,
>
> Thanks for the reply. The general idea that you had for adding partitions
> is similar to what we had in mind. It would be useful to make this more
> general, allowing adding an arbitrary number of partitions (instead of just
> doubling) and potentially removing partitions as well. The following is the
> high level idea from the discussion with Colin, Jason and Ismael.
>
> * To change the number of partitions from X to Y in a topic, the controller
> marks all existing X partitions as read-only and creates Y new partitions.
> The new partitions are writable and are tagged with a higher repartition
> epoch (RE).
>
> * The controller propagates the new metadata to every broker. Once the
> leader of a partition is marked as read-only, it rejects the produce
> requests on this partition. The producer will then refresh the metadata and
> start publishing to the new writable partitions.
>
> * The consumers will then be consuming messages in RE order. The consumer
> coordinator will only assign partitions in the same RE to consumers. Only
> after all messages in an RE are consumed, will partitions in a higher RE be
> assigned to consumers.
>
> As Colin mentioned, if we do the above, we could potentially (1) use a
> globally unique partition id, or (2) use a globally unique topic id to
> distinguish recreated partitions due to topic deletion.
>
> So, perhaps we can sketch out the re-partitioning KIP a bit more and see if
> there is any overlap with KIP-232. Would you be interested in doing that?
> If not, we can do that next week.
>
> Jun
>
>
> On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin  wrote:
>
> > Hey Jun,
> >
> > Interestingly I am also planning to sketch a KIP to allow partition
> > expansion for keyed topics after this KIP. Since you are already doing
> > that, I guess I will just share my high level idea here in case it is
> > helpful.
> >
> > The motivation for the KIP is that we currently lose order guarantee for
> > messages with the same key if we expand partitions of keyed topic.
> >
> > The solution can probably be built upon the following ideas:
> >
> > - Partition number of the keyed topic should always be doubled (or
> > multiplied by power of 2). Given that we select a partition based on
> > hash(key) % partitionNum, this should help us ensure that, a message
> > assigned to an existing partition will not be mapped to another existing
> > partition after partition expansion.
> >
> > - Producer includes in the ProduceRequest some information that helps
> > ensure that messages produced ti a partition will monotonically increase
> in
> > the partitionNum of the topic. In other words, if broker receives a
> > ProduceRequest and notices that the producer does not know the partition
> > number has increased, broker should reject this request. That
> "information"
> > maybe leaderEpoch, max partitionEpoch of the partitions of the topic, or
> > simply partitionNum of the topic. The benefit of this property is that we
> > can keep the new logic for in-order message consumption entirely in how
> > consumer leader determines the partition -> consumer mapping.
> >
> > - When consumer leader determines partition -> consumer mapping, leader
> > first reads the start position for each partition using
> OffsetFetchRequest.
> > If start position are all non-zero, then assignment can be done in its
> > current manner. The assumption is that, a message in the new partition
> > should only be consumed after all messages with the same key produced
> > before it has been consumed. Since some messages in the new partition has
> > been consumed, we should not worry about consuming messages out-of-order.
> > This benefit of this approach is that we can avoid unnecessary overhead
> in
> > the common case.
> >
> > - If the consumer leader finds that the start position for some partition
> > is 0. Say the current partition number is 18 and the partition index is
> 12,
> > then consumer leader should ensure that messages produced to partition
> 12 -
> > 18/2 = 3 before the first message of partition 12 is consumed, before it
> > assigned partition 12 to any consumer in the consumer group. Since we
> have
> > a "information" that is monotonically increasing per partition, consumer
> > can read the value of this information from the first message in
> partition
> > 12, get the offset corresponding to this value in partition 3, assign
> > partition except for partition 12 (and probably other new partitions) to
> > the existing consumers, waiting for the committed offset to go beyond
> this
> > offset for partition 3, and trigger rebalance again so that partition 3
> can
> > be reassigned to some consumer.
> 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Jun Rao]

Hi, Dong,

Thanks for the reply. The general idea that you had for adding partitions
is similar to what we had in mind. It would be useful to make this more
general, allowing adding an arbitrary number of partitions (instead of just
doubling) and potentially removing partitions as well. The following is the
high level idea from the discussion with Colin, Jason and Ismael.

* To change the number of partitions from X to Y in a topic, the controller
marks all existing X partitions as read-only and creates Y new partitions.
The new partitions are writable and are tagged with a higher repartition
epoch (RE).

* The controller propagates the new metadata to every broker. Once the
leader of a partition is marked as read-only, it rejects the produce
requests on this partition. The producer will then refresh the metadata and
start publishing to the new writable partitions.

* The consumers will then be consuming messages in RE order. The consumer
coordinator will only assign partitions in the same RE to consumers. Only
after all messages in an RE are consumed, will partitions in a higher RE be
assigned to consumers.

As Colin mentioned, if we do the above, we could potentially (1) use a
globally unique partition id, or (2) use a globally unique topic id to
distinguish recreated partitions due to topic deletion.

So, perhaps we can sketch out the re-partitioning KIP a bit more and see if
there is any overlap with KIP-232. Would you be interested in doing that?
If not, we can do that next week.

Jun


On Tue, Feb 6, 2018 at 11:30 AM, Dong Lin  wrote:

> Hey Jun,
>
> Interestingly I am also planning to sketch a KIP to allow partition
> expansion for keyed topics after this KIP. Since you are already doing
> that, I guess I will just share my high level idea here in case it is
> helpful.
>
> The motivation for the KIP is that we currently lose order guarantee for
> messages with the same key if we expand partitions of keyed topic.
>
> The solution can probably be built upon the following ideas:
>
> - Partition number of the keyed topic should always be doubled (or
> multiplied by power of 2). Given that we select a partition based on
> hash(key) % partitionNum, this should help us ensure that, a message
> assigned to an existing partition will not be mapped to another existing
> partition after partition expansion.
>
> - Producer includes in the ProduceRequest some information that helps
> ensure that messages produced ti a partition will monotonically increase in
> the partitionNum of the topic. In other words, if broker receives a
> ProduceRequest and notices that the producer does not know the partition
> number has increased, broker should reject this request. That "information"
> maybe leaderEpoch, max partitionEpoch of the partitions of the topic, or
> simply partitionNum of the topic. The benefit of this property is that we
> can keep the new logic for in-order message consumption entirely in how
> consumer leader determines the partition -> consumer mapping.
>
> - When consumer leader determines partition -> consumer mapping, leader
> first reads the start position for each partition using OffsetFetchRequest.
> If start position are all non-zero, then assignment can be done in its
> current manner. The assumption is that, a message in the new partition
> should only be consumed after all messages with the same key produced
> before it has been consumed. Since some messages in the new partition has
> been consumed, we should not worry about consuming messages out-of-order.
> This benefit of this approach is that we can avoid unnecessary overhead in
> the common case.
>
> - If the consumer leader finds that the start position for some partition
> is 0. Say the current partition number is 18 and the partition index is 12,
> then consumer leader should ensure that messages produced to partition 12 -
> 18/2 = 3 before the first message of partition 12 is consumed, before it
> assigned partition 12 to any consumer in the consumer group. Since we have
> a "information" that is monotonically increasing per partition, consumer
> can read the value of this information from the first message in partition
> 12, get the offset corresponding to this value in partition 3, assign
> partition except for partition 12 (and probably other new partitions) to
> the existing consumers, waiting for the committed offset to go beyond this
> offset for partition 3, and trigger rebalance again so that partition 3 can
> be reassigned to some consumer.
>
>
> Thanks,
> Dong
>
>
> On Tue, Feb 6, 2018 at 10:10 AM, Jun Rao  wrote:
>
> > Hi, Dong,
> >
> > Thanks for the KIP. It looks good overall. We are working on a separate
> KIP
> > for adding partitions while preserving the ordering guarantees. That may
> > require another flavor of partition epoch. It's not very clear whether
> that
> > partition epoch can be merged with the partition epoch in this KIP. So,
> > perhaps you can wait on this a bit 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

Hi Becket,

I would argue that using IDs for partitions is not a performance improvement, 
but actually a completely different way of accomplishing what this KIP is 
trying to solve.  If you give partitions globally unique IDs, and use a 
different ID when re-creating a topic partition, you don't need a partition 
epoch to distinguish between the first incarnation of a topic.  I think there 
are some advantages and disadvantages to both approaches.

One thing that isn't clear to me is whether a 32-bit number would be enough for 
a partition epoch.  If I understand correctly, the partition epoch for a newly 
created partition is taken from a global counter maintained in ZK.  So I would 
expect a 32 or 31 bit counter to potentially wrap around if there are a lot of 
partition creations and deletions.

best,
Colin


On Mon, Feb 5, 2018, at 14:43, Becket Qin wrote:
> +1 on the KIP.
> 
> I think the KIP is mainly about adding the capability of tracking the
> system state change lineage. It does not seem necessary to bundle this KIP
> with replacing the topic partition with partition epoch in produce/fetch.
> Replacing topic-partition string with partition epoch is essentially a
> performance improvement on top of this KIP. That can probably be done
> separately.
> 
> Thanks,
> 
> Jiangjie (Becket) Qin
> 
> On Mon, Jan 29, 2018 at 11:52 AM, Dong Lin  wrote:
> 
> > Hey Colin,
> >
> > On Mon, Jan 29, 2018 at 11:23 AM, Colin McCabe  wrote:
> >
> > > > On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin 
> > wrote:
> > > >
> > > > > Hey Colin,
> > > > >
> > > > > I understand that the KIP will adds overhead by introducing
> > > per-partition
> > > > > partitionEpoch. I am open to alternative solutions that does not
> > incur
> > > > > additional overhead. But I don't see a better way now.
> > > > >
> > > > > IMO the overhead in the FetchResponse may not be that much. We
> > probably
> > > > > should discuss the percentage increase rather than the absolute
> > number
> > > > > increase. Currently after KIP-227, per-partition header has 23 bytes.
> > > This
> > > > > KIP adds another 4 bytes. Assume the records size is 10KB, the
> > > percentage
> > > > > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
> > >
> > > Hi Dong,
> > >
> > > Thanks for the response.  I agree that the FetchRequest / FetchResponse
> > > overhead should be OK, now that we have incremental fetch requests and
> > > responses.  However, there are a lot of cases where the percentage
> > increase
> > > is much greater.  For example, if a client is doing full
> > MetadataRequests /
> > > Responses, we have some math kind of like this per partition:
> > >
> > > > UpdateMetadataRequestPartitionState => topic partition
> > controller_epoch
> > > leader  leader_epoch partition_epoch isr zk_version replicas
> > > offline_replicas
> > > > 14 bytes:  topic => string (assuming about 10 byte topic names)
> > > > 4 bytes:  partition => int32
> > > > 4  bytes: conroller_epoch => int32
> > > > 4  bytes: leader => int32
> > > > 4  bytes: leader_epoch => int32
> > > > +4 EXTRA bytes: partition_epoch => int32<-- NEW
> > > > 2+4+4+4 bytes: isr => [int32] (assuming 3 in the ISR)
> > > > 4 bytes: zk_version => int32
> > > > 2+4+4+4 bytes: replicas => [int32] (assuming 3 replicas)
> > > > 2  offline_replicas => [int32] (assuming no offline replicas)
> > >
> > > Assuming I added that up correctly, the per-partition overhead goes from
> > > 64 bytes per partition to 68, a 6.2% increase.
> > >
> > > We could do similar math for a lot of the other RPCs.  And you will have
> > a
> > > similar memory and garbage collection impact on the brokers since you
> > have
> > > to store all this extra state as well.
> > >
> >
> > That is correct. IMO the Metadata is only updated periodically and is
> > probably not a big deal if we increase it by 6%. The FetchResponse and
> > ProduceRequest are probably the only requests that are bounded by the
> > bandwidth throughput.
> >
> >
> > >
> > > > >
> > > > > I agree that we can probably save more space by using partition ID so
> > > that
> > > > > we no longer needs the string topic name. The similar idea has also
> > > been
> > > > > put in the Rejected Alternative section in KIP-227. While this idea
> > is
> > > > > promising, it seems orthogonal to the goal of this KIP. Given that
> > > there is
> > > > > already many work to do in this KIP, maybe we can do the partition ID
> > > in a
> > > > > separate KIP?
> > >
> > > I guess my thinking is that the goal here is to replace an identifier
> > > which can be re-used (the tuple of topic name, partition ID) with an
> > > identifier that cannot be re-used (the tuple of topic name, partition ID,
> > > partition epoch) in order to gain better semantics.  As long as we are
> > > replacing the identifier, why not replace it with an identifier that has
> > > important performance advantages?  The KIP freeze for the 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Jun,

Interestingly I am also planning to sketch a KIP to allow partition
expansion for keyed topics after this KIP. Since you are already doing
that, I guess I will just share my high level idea here in case it is
helpful.

The motivation for the KIP is that we currently lose order guarantee for
messages with the same key if we expand partitions of keyed topic.

The solution can probably be built upon the following ideas:

- Partition number of the keyed topic should always be doubled (or
multiplied by power of 2). Given that we select a partition based on
hash(key) % partitionNum, this should help us ensure that, a message
assigned to an existing partition will not be mapped to another existing
partition after partition expansion.

- Producer includes in the ProduceRequest some information that helps
ensure that messages produced ti a partition will monotonically increase in
the partitionNum of the topic. In other words, if broker receives a
ProduceRequest and notices that the producer does not know the partition
number has increased, broker should reject this request. That "information"
maybe leaderEpoch, max partitionEpoch of the partitions of the topic, or
simply partitionNum of the topic. The benefit of this property is that we
can keep the new logic for in-order message consumption entirely in how
consumer leader determines the partition -> consumer mapping.

- When consumer leader determines partition -> consumer mapping, leader
first reads the start position for each partition using OffsetFetchRequest.
If start position are all non-zero, then assignment can be done in its
current manner. The assumption is that, a message in the new partition
should only be consumed after all messages with the same key produced
before it has been consumed. Since some messages in the new partition has
been consumed, we should not worry about consuming messages out-of-order.
This benefit of this approach is that we can avoid unnecessary overhead in
the common case.

- If the consumer leader finds that the start position for some partition
is 0. Say the current partition number is 18 and the partition index is 12,
then consumer leader should ensure that messages produced to partition 12 -
18/2 = 3 before the first message of partition 12 is consumed, before it
assigned partition 12 to any consumer in the consumer group. Since we have
a "information" that is monotonically increasing per partition, consumer
can read the value of this information from the first message in partition
12, get the offset corresponding to this value in partition 3, assign
partition except for partition 12 (and probably other new partitions) to
the existing consumers, waiting for the committed offset to go beyond this
offset for partition 3, and trigger rebalance again so that partition 3 can
be reassigned to some consumer.


Thanks,
Dong


On Tue, Feb 6, 2018 at 10:10 AM, Jun Rao  wrote:

> Hi, Dong,
>
> Thanks for the KIP. It looks good overall. We are working on a separate KIP
> for adding partitions while preserving the ordering guarantees. That may
> require another flavor of partition epoch. It's not very clear whether that
> partition epoch can be merged with the partition epoch in this KIP. So,
> perhaps you can wait on this a bit until we post the other KIP in the next
> few days.
>
> Jun
>
>
>
> On Mon, Feb 5, 2018 at 2:43 PM, Becket Qin  wrote:
>
> > +1 on the KIP.
> >
> > I think the KIP is mainly about adding the capability of tracking the
> > system state change lineage. It does not seem necessary to bundle this
> KIP
> > with replacing the topic partition with partition epoch in produce/fetch.
> > Replacing topic-partition string with partition epoch is essentially a
> > performance improvement on top of this KIP. That can probably be done
> > separately.
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> > On Mon, Jan 29, 2018 at 11:52 AM, Dong Lin  wrote:
> >
> > > Hey Colin,
> > >
> > > On Mon, Jan 29, 2018 at 11:23 AM, Colin McCabe 
> > wrote:
> > >
> > > > > On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin 
> > > wrote:
> > > > >
> > > > > > Hey Colin,
> > > > > >
> > > > > > I understand that the KIP will adds overhead by introducing
> > > > per-partition
> > > > > > partitionEpoch. I am open to alternative solutions that does not
> > > incur
> > > > > > additional overhead. But I don't see a better way now.
> > > > > >
> > > > > > IMO the overhead in the FetchResponse may not be that much. We
> > > probably
> > > > > > should discuss the percentage increase rather than the absolute
> > > number
> > > > > > increase. Currently after KIP-227, per-partition header has 23
> > bytes.
> > > > This
> > > > > > KIP adds another 4 bytes. Assume the records size is 10KB, the
> > > > percentage
> > > > > > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
> > > >
> > > > Hi Dong,
> > > >
> > > > Thanks for the 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Jun Rao]

Hi, Dong,

Thanks for the KIP. It looks good overall. We are working on a separate KIP
for adding partitions while preserving the ordering guarantees. That may
require another flavor of partition epoch. It's not very clear whether that
partition epoch can be merged with the partition epoch in this KIP. So,
perhaps you can wait on this a bit until we post the other KIP in the next
few days.

Jun



On Mon, Feb 5, 2018 at 2:43 PM, Becket Qin  wrote:

> +1 on the KIP.
>
> I think the KIP is mainly about adding the capability of tracking the
> system state change lineage. It does not seem necessary to bundle this KIP
> with replacing the topic partition with partition epoch in produce/fetch.
> Replacing topic-partition string with partition epoch is essentially a
> performance improvement on top of this KIP. That can probably be done
> separately.
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
> On Mon, Jan 29, 2018 at 11:52 AM, Dong Lin  wrote:
>
> > Hey Colin,
> >
> > On Mon, Jan 29, 2018 at 11:23 AM, Colin McCabe 
> wrote:
> >
> > > > On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin 
> > wrote:
> > > >
> > > > > Hey Colin,
> > > > >
> > > > > I understand that the KIP will adds overhead by introducing
> > > per-partition
> > > > > partitionEpoch. I am open to alternative solutions that does not
> > incur
> > > > > additional overhead. But I don't see a better way now.
> > > > >
> > > > > IMO the overhead in the FetchResponse may not be that much. We
> > probably
> > > > > should discuss the percentage increase rather than the absolute
> > number
> > > > > increase. Currently after KIP-227, per-partition header has 23
> bytes.
> > > This
> > > > > KIP adds another 4 bytes. Assume the records size is 10KB, the
> > > percentage
> > > > > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
> > >
> > > Hi Dong,
> > >
> > > Thanks for the response.  I agree that the FetchRequest / FetchResponse
> > > overhead should be OK, now that we have incremental fetch requests and
> > > responses.  However, there are a lot of cases where the percentage
> > increase
> > > is much greater.  For example, if a client is doing full
> > MetadataRequests /
> > > Responses, we have some math kind of like this per partition:
> > >
> > > > UpdateMetadataRequestPartitionState => topic partition
> > controller_epoch
> > > leader  leader_epoch partition_epoch isr zk_version replicas
> > > offline_replicas
> > > > 14 bytes:  topic => string (assuming about 10 byte topic names)
> > > > 4 bytes:  partition => int32
> > > > 4  bytes: conroller_epoch => int32
> > > > 4  bytes: leader => int32
> > > > 4  bytes: leader_epoch => int32
> > > > +4 EXTRA bytes: partition_epoch => int32<-- NEW
> > > > 2+4+4+4 bytes: isr => [int32] (assuming 3 in the ISR)
> > > > 4 bytes: zk_version => int32
> > > > 2+4+4+4 bytes: replicas => [int32] (assuming 3 replicas)
> > > > 2  offline_replicas => [int32] (assuming no offline replicas)
> > >
> > > Assuming I added that up correctly, the per-partition overhead goes
> from
> > > 64 bytes per partition to 68, a 6.2% increase.
> > >
> > > We could do similar math for a lot of the other RPCs.  And you will
> have
> > a
> > > similar memory and garbage collection impact on the brokers since you
> > have
> > > to store all this extra state as well.
> > >
> >
> > That is correct. IMO the Metadata is only updated periodically and is
> > probably not a big deal if we increase it by 6%. The FetchResponse and
> > ProduceRequest are probably the only requests that are bounded by the
> > bandwidth throughput.
> >
> >
> > >
> > > > >
> > > > > I agree that we can probably save more space by using partition ID
> so
> > > that
> > > > > we no longer needs the string topic name. The similar idea has also
> > > been
> > > > > put in the Rejected Alternative section in KIP-227. While this idea
> > is
> > > > > promising, it seems orthogonal to the goal of this KIP. Given that
> > > there is
> > > > > already many work to do in this KIP, maybe we can do the partition
> ID
> > > in a
> > > > > separate KIP?
> > >
> > > I guess my thinking is that the goal here is to replace an identifier
> > > which can be re-used (the tuple of topic name, partition ID) with an
> > > identifier that cannot be re-used (the tuple of topic name, partition
> ID,
> > > partition epoch) in order to gain better semantics.  As long as we are
> > > replacing the identifier, why not replace it with an identifier that
> has
> > > important performance advantages?  The KIP freeze for the next release
> > has
> > > already passed, so there is time to do this.
> > >
> >
> > In general it can be easier for discussion and implementation if we can
> > split a larger task into smaller and independent tasks. For example,
> > KIP-112 and KIP-113 both deals with the JBOD support. KIP-31, KIP-32 and
> > KIP-33 are about timestamp support. The option on this can be subject
> > 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Becket Qin]

+1 on the KIP.

I think the KIP is mainly about adding the capability of tracking the
system state change lineage. It does not seem necessary to bundle this KIP
with replacing the topic partition with partition epoch in produce/fetch.
Replacing topic-partition string with partition epoch is essentially a
performance improvement on top of this KIP. That can probably be done
separately.

Thanks,

Jiangjie (Becket) Qin

On Mon, Jan 29, 2018 at 11:52 AM, Dong Lin  wrote:

> Hey Colin,
>
> On Mon, Jan 29, 2018 at 11:23 AM, Colin McCabe  wrote:
>
> > > On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin 
> wrote:
> > >
> > > > Hey Colin,
> > > >
> > > > I understand that the KIP will adds overhead by introducing
> > per-partition
> > > > partitionEpoch. I am open to alternative solutions that does not
> incur
> > > > additional overhead. But I don't see a better way now.
> > > >
> > > > IMO the overhead in the FetchResponse may not be that much. We
> probably
> > > > should discuss the percentage increase rather than the absolute
> number
> > > > increase. Currently after KIP-227, per-partition header has 23 bytes.
> > This
> > > > KIP adds another 4 bytes. Assume the records size is 10KB, the
> > percentage
> > > > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
> >
> > Hi Dong,
> >
> > Thanks for the response.  I agree that the FetchRequest / FetchResponse
> > overhead should be OK, now that we have incremental fetch requests and
> > responses.  However, there are a lot of cases where the percentage
> increase
> > is much greater.  For example, if a client is doing full
> MetadataRequests /
> > Responses, we have some math kind of like this per partition:
> >
> > > UpdateMetadataRequestPartitionState => topic partition
> controller_epoch
> > leader  leader_epoch partition_epoch isr zk_version replicas
> > offline_replicas
> > > 14 bytes:  topic => string (assuming about 10 byte topic names)
> > > 4 bytes:  partition => int32
> > > 4  bytes: conroller_epoch => int32
> > > 4  bytes: leader => int32
> > > 4  bytes: leader_epoch => int32
> > > +4 EXTRA bytes: partition_epoch => int32<-- NEW
> > > 2+4+4+4 bytes: isr => [int32] (assuming 3 in the ISR)
> > > 4 bytes: zk_version => int32
> > > 2+4+4+4 bytes: replicas => [int32] (assuming 3 replicas)
> > > 2  offline_replicas => [int32] (assuming no offline replicas)
> >
> > Assuming I added that up correctly, the per-partition overhead goes from
> > 64 bytes per partition to 68, a 6.2% increase.
> >
> > We could do similar math for a lot of the other RPCs.  And you will have
> a
> > similar memory and garbage collection impact on the brokers since you
> have
> > to store all this extra state as well.
> >
>
> That is correct. IMO the Metadata is only updated periodically and is
> probably not a big deal if we increase it by 6%. The FetchResponse and
> ProduceRequest are probably the only requests that are bounded by the
> bandwidth throughput.
>
>
> >
> > > >
> > > > I agree that we can probably save more space by using partition ID so
> > that
> > > > we no longer needs the string topic name. The similar idea has also
> > been
> > > > put in the Rejected Alternative section in KIP-227. While this idea
> is
> > > > promising, it seems orthogonal to the goal of this KIP. Given that
> > there is
> > > > already many work to do in this KIP, maybe we can do the partition ID
> > in a
> > > > separate KIP?
> >
> > I guess my thinking is that the goal here is to replace an identifier
> > which can be re-used (the tuple of topic name, partition ID) with an
> > identifier that cannot be re-used (the tuple of topic name, partition ID,
> > partition epoch) in order to gain better semantics.  As long as we are
> > replacing the identifier, why not replace it with an identifier that has
> > important performance advantages?  The KIP freeze for the next release
> has
> > already passed, so there is time to do this.
> >
>
> In general it can be easier for discussion and implementation if we can
> split a larger task into smaller and independent tasks. For example,
> KIP-112 and KIP-113 both deals with the JBOD support. KIP-31, KIP-32 and
> KIP-33 are about timestamp support. The option on this can be subject
> though.
>
> IMO the change to switch from (topic, partition ID) to partitionEpch in all
> request/response requires us to going through all request one by one. It
> may not be hard but it can be time consuming and tedious. At high level the
> goal and the change for that will be orthogonal to the changes required in
> this KIP. That is the main reason I think we can split them into two KIPs.
>
>
> > On Mon, Jan 29, 2018, at 10:54, Dong Lin wrote:
> > > I think it is possible to move to entirely use partitionEpoch instead
> of
> > > (topic, partition) to identify a partition. Client can obtain the
> > > partitionEpoch -> (topic, partition) mapping from MetadataResponse. We
> > > probably need to 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Colin,

On Mon, Jan 29, 2018 at 11:23 AM, Colin McCabe  wrote:

> > On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin  wrote:
> >
> > > Hey Colin,
> > >
> > > I understand that the KIP will adds overhead by introducing
> per-partition
> > > partitionEpoch. I am open to alternative solutions that does not incur
> > > additional overhead. But I don't see a better way now.
> > >
> > > IMO the overhead in the FetchResponse may not be that much. We probably
> > > should discuss the percentage increase rather than the absolute number
> > > increase. Currently after KIP-227, per-partition header has 23 bytes.
> This
> > > KIP adds another 4 bytes. Assume the records size is 10KB, the
> percentage
> > > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
>
> Hi Dong,
>
> Thanks for the response.  I agree that the FetchRequest / FetchResponse
> overhead should be OK, now that we have incremental fetch requests and
> responses.  However, there are a lot of cases where the percentage increase
> is much greater.  For example, if a client is doing full MetadataRequests /
> Responses, we have some math kind of like this per partition:
>
> > UpdateMetadataRequestPartitionState => topic partition controller_epoch
> leader  leader_epoch partition_epoch isr zk_version replicas
> offline_replicas
> > 14 bytes:  topic => string (assuming about 10 byte topic names)
> > 4 bytes:  partition => int32
> > 4  bytes: conroller_epoch => int32
> > 4  bytes: leader => int32
> > 4  bytes: leader_epoch => int32
> > +4 EXTRA bytes: partition_epoch => int32<-- NEW
> > 2+4+4+4 bytes: isr => [int32] (assuming 3 in the ISR)
> > 4 bytes: zk_version => int32
> > 2+4+4+4 bytes: replicas => [int32] (assuming 3 replicas)
> > 2  offline_replicas => [int32] (assuming no offline replicas)
>
> Assuming I added that up correctly, the per-partition overhead goes from
> 64 bytes per partition to 68, a 6.2% increase.
>
> We could do similar math for a lot of the other RPCs.  And you will have a
> similar memory and garbage collection impact on the brokers since you have
> to store all this extra state as well.
>

That is correct. IMO the Metadata is only updated periodically and is
probably not a big deal if we increase it by 6%. The FetchResponse and
ProduceRequest are probably the only requests that are bounded by the
bandwidth throughput.


>
> > >
> > > I agree that we can probably save more space by using partition ID so
> that
> > > we no longer needs the string topic name. The similar idea has also
> been
> > > put in the Rejected Alternative section in KIP-227. While this idea is
> > > promising, it seems orthogonal to the goal of this KIP. Given that
> there is
> > > already many work to do in this KIP, maybe we can do the partition ID
> in a
> > > separate KIP?
>
> I guess my thinking is that the goal here is to replace an identifier
> which can be re-used (the tuple of topic name, partition ID) with an
> identifier that cannot be re-used (the tuple of topic name, partition ID,
> partition epoch) in order to gain better semantics.  As long as we are
> replacing the identifier, why not replace it with an identifier that has
> important performance advantages?  The KIP freeze for the next release has
> already passed, so there is time to do this.
>

In general it can be easier for discussion and implementation if we can
split a larger task into smaller and independent tasks. For example,
KIP-112 and KIP-113 both deals with the JBOD support. KIP-31, KIP-32 and
KIP-33 are about timestamp support. The option on this can be subject
though.

IMO the change to switch from (topic, partition ID) to partitionEpch in all
request/response requires us to going through all request one by one. It
may not be hard but it can be time consuming and tedious. At high level the
goal and the change for that will be orthogonal to the changes required in
this KIP. That is the main reason I think we can split them into two KIPs.


> On Mon, Jan 29, 2018, at 10:54, Dong Lin wrote:
> > I think it is possible to move to entirely use partitionEpoch instead of
> > (topic, partition) to identify a partition. Client can obtain the
> > partitionEpoch -> (topic, partition) mapping from MetadataResponse. We
> > probably need to figure out a way to assign partitionEpoch to existing
> > partitions in the cluster. But this should be doable.
> >
> > This is a good idea. I think it will save us some space in the
> > request/response. The actual space saving in percentage probably depends
> on
> > the amount of data and the number of partitions of the same topic. I just
> > think we can do it in a separate KIP.
>
> Hmm.  How much extra work would be required?  It seems like we are already
> changing almost every RPC that involves topics and partitions, already
> adding new per-partition state to ZooKeeper, already changing how clients
> interact with partitions.  Is there some other big piece of work we'd have
> to do to move 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

> On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin  wrote:
> 
> > Hey Colin,
> >
> > I understand that the KIP will adds overhead by introducing per-partition
> > partitionEpoch. I am open to alternative solutions that does not incur
> > additional overhead. But I don't see a better way now.
> >
> > IMO the overhead in the FetchResponse may not be that much. We probably
> > should discuss the percentage increase rather than the absolute number
> > increase. Currently after KIP-227, per-partition header has 23 bytes. This
> > KIP adds another 4 bytes. Assume the records size is 10KB, the percentage
> > increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?

Hi Dong,

Thanks for the response.  I agree that the FetchRequest / FetchResponse 
overhead should be OK, now that we have incremental fetch requests and 
responses.  However, there are a lot of cases where the percentage increase is 
much greater.  For example, if a client is doing full MetadataRequests / 
Responses, we have some math kind of like this per partition:

> UpdateMetadataRequestPartitionState => topic partition controller_epoch 
> leader  leader_epoch partition_epoch isr zk_version replicas offline_replicas
> 14 bytes:  topic => string (assuming about 10 byte topic names)
> 4 bytes:  partition => int32
> 4  bytes: conroller_epoch => int32
> 4  bytes: leader => int32
> 4  bytes: leader_epoch => int32
> +4 EXTRA bytes: partition_epoch => int32<-- NEW
> 2+4+4+4 bytes: isr => [int32] (assuming 3 in the ISR)
> 4 bytes: zk_version => int32
> 2+4+4+4 bytes: replicas => [int32] (assuming 3 replicas)
> 2  offline_replicas => [int32] (assuming no offline replicas)

Assuming I added that up correctly, the per-partition overhead goes from 64 
bytes per partition to 68, a 6.2% increase.

We could do similar math for a lot of the other RPCs.  And you will have a 
similar memory and garbage collection impact on the brokers since you have to 
store all this extra state as well.

> >
> > I agree that we can probably save more space by using partition ID so that
> > we no longer needs the string topic name. The similar idea has also been
> > put in the Rejected Alternative section in KIP-227. While this idea is
> > promising, it seems orthogonal to the goal of this KIP. Given that there is
> > already many work to do in this KIP, maybe we can do the partition ID in a
> > separate KIP?

I guess my thinking is that the goal here is to replace an identifier which can 
be re-used (the tuple of topic name, partition ID) with an identifier that 
cannot be re-used (the tuple of topic name, partition ID, partition epoch) in 
order to gain better semantics.  As long as we are replacing the identifier, 
why not replace it with an identifier that has important performance 
advantages?  The KIP freeze for the next release has already passed, so there 
is time to do this.

On Mon, Jan 29, 2018, at 10:54, Dong Lin wrote:
> I think it is possible to move to entirely use partitionEpoch instead of
> (topic, partition) to identify a partition. Client can obtain the
> partitionEpoch -> (topic, partition) mapping from MetadataResponse. We
> probably need to figure out a way to assign partitionEpoch to existing
> partitions in the cluster. But this should be doable.
> 
> This is a good idea. I think it will save us some space in the
> request/response. The actual space saving in percentage probably depends on
> the amount of data and the number of partitions of the same topic. I just
> think we can do it in a separate KIP.

Hmm.  How much extra work would be required?  It seems like we are already 
changing almost every RPC that involves topics and partitions, already adding 
new per-partition state to ZooKeeper, already changing how clients interact 
with partitions.  Is there some other big piece of work we'd have to do to move 
to partition IDs that we wouldn't need for partition epochs?  I guess we'd have 
to find a way to support regular expression-based topic subscriptions.  If we 
split this into multiple KIPs, wouldn't we end up changing all that RPCs and ZK 
state a second time?  Also, I'm curious if anyone has done any proof of concept 
GC, memory, and network usage measurements on switching topic names for topic 
IDs.

best,
Colin

> 
> 
> 
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > On Mon, Jan 29, 2018 at 10:18 AM, Colin McCabe  wrote:
> >
> >> On Fri, Jan 26, 2018, at 12:17, Dong Lin wrote:
> >> > Hey Colin,
> >> >
> >> >
> >> > On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe 
> >> wrote:
> >> >
> >> > > On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> >> > > > Hey Colin,
> >> > > >
> >> > > > Thanks for the comment.
> >> > > >
> >> > > > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
> >> > > wrote:
> >> > > >
> >> > > > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> >> > > > > > Hey Colin,
> >> > > > > >
> >> > > > > > Thanks for reviewing the KIP.
> >> > > > > >
> 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

I think it is possible to move to entirely use partitionEpoch instead of
(topic, partition) to identify a partition. Client can obtain the
partitionEpoch -> (topic, partition) mapping from MetadataResponse. We
probably need to figure out a way to assign partitionEpoch to existing
partitions in the cluster. But this should be doable.

This is a good idea. I think it will save us some space in the
request/response. The actual space saving in percentage probably depends on
the amount of data and the number of partitions of the same topic. I just
think we can do it in a separate KIP.



On Mon, Jan 29, 2018 at 10:35 AM, Dong Lin  wrote:

> Hey Colin,
>
> I understand that the KIP will adds overhead by introducing per-partition
> partitionEpoch. I am open to alternative solutions that does not incur
> additional overhead. But I don't see a better way now.
>
> IMO the overhead in the FetchResponse may not be that much. We probably
> should discuss the percentage increase rather than the absolute number
> increase. Currently after KIP-227, per-partition header has 23 bytes. This
> KIP adds another 4 bytes. Assume the records size is 10KB, the percentage
> increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?
>
> I agree that we can probably save more space by using partition ID so that
> we no longer needs the string topic name. The similar idea has also been
> put in the Rejected Alternative section in KIP-227. While this idea is
> promising, it seems orthogonal to the goal of this KIP. Given that there is
> already many work to do in this KIP, maybe we can do the partition ID in a
> separate KIP?
>
> Thanks,
> Dong
>
>
>
>
>
>
>
>
>
>
> On Mon, Jan 29, 2018 at 10:18 AM, Colin McCabe  wrote:
>
>> On Fri, Jan 26, 2018, at 12:17, Dong Lin wrote:
>> > Hey Colin,
>> >
>> >
>> > On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe 
>> wrote:
>> >
>> > > On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
>> > > > Hey Colin,
>> > > >
>> > > > Thanks for the comment.
>> > > >
>> > > > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
>> > > wrote:
>> > > >
>> > > > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
>> > > > > > Hey Colin,
>> > > > > >
>> > > > > > Thanks for reviewing the KIP.
>> > > > > >
>> > > > > > If I understand you right, you maybe suggesting that we can use
>> a
>> > > global
>> > > > > > metadataEpoch that is incremented every time controller updates
>> > > metadata.
>> > > > > > The problem with this solution is that, if a topic is deleted
>> and
>> > > created
>> > > > > > again, user will not know whether that the offset which is
>> stored
>> > > before
>> > > > > > the topic deletion is no longer valid. This motivates the idea
>> to
>> > > include
>> > > > > > per-partition partitionEpoch. Does this sound reasonable?
>> > > > >
>> > > > > Hi Dong,
>> > > > >
>> > > > > Perhaps we can store the last valid offset of each deleted topic
>> in
>> > > > > ZooKeeper.  Then, when a topic with one of those names gets
>> > > re-created, we
>> > > > > can start the topic at the previous end offset rather than at 0.
>> This
>> > > > > preserves immutability.  It is no more burdensome than having to
>> > > preserve a
>> > > > > "last epoch" for the deleted partition somewhere, right?
>> > > > >
>> > > >
>> > > > My concern with this solution is that the number of zookeeper nodes
>> get
>> > > > more and more over time if some users keep deleting and creating
>> topics.
>> > > Do
>> > > > you think this can be a problem?
>> > >
>> > > Hi Dong,
>> > >
>> > > We could expire the "partition tombstones" after an hour or so.  In
>> > > practice this would solve the issue for clients that like to destroy
>> and
>> > > re-create topics all the time.  In any case, doesn't the current
>> proposal
>> > > add per-partition znodes as well that we have to track even after the
>> > > partition is deleted?  Or did I misunderstand that?
>> > >
>> >
>> > Actually the current KIP does not add per-partition znodes. Could you
>> > double check? I can fix the KIP wiki if there is anything misleading.
>>
>> Hi Dong,
>>
>> I double-checked the KIP, and I can see that you are in fact using a
>> global counter for initializing partition epochs.  So, you are correct, it
>> doesn't add per-partition znodes for partitions that no longer exist.
>>
>> >
>> > If we expire the "partition tomstones" after an hour, and the topic is
>> > re-created after more than an hour since the topic deletion, then we are
>> > back to the situation where user can not tell whether the topic has been
>> > re-created or not, right?
>>
>> Yes, with an expiration period, it would not ensure immutability-- you
>> could effectively reuse partition names and they would look the same.
>>
>> >
>> >
>> > >
>> > > It's not really clear to me what should happen when a topic is
>> destroyed
>> > > and re-created with new data.  Should consumers continue to be able to
>> > > consume?  

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Colin,

I understand that the KIP will adds overhead by introducing per-partition
partitionEpoch. I am open to alternative solutions that does not incur
additional overhead. But I don't see a better way now.

IMO the overhead in the FetchResponse may not be that much. We probably
should discuss the percentage increase rather than the absolute number
increase. Currently after KIP-227, per-partition header has 23 bytes. This
KIP adds another 4 bytes. Assume the records size is 10KB, the percentage
increase is 4 / (23 + 1) = 0.03%. It seems negligible, right?

I agree that we can probably save more space by using partition ID so that
we no longer needs the string topic name. The similar idea has also been
put in the Rejected Alternative section in KIP-227. While this idea is
promising, it seems orthogonal to the goal of this KIP. Given that there is
already many work to do in this KIP, maybe we can do the partition ID in a
separate KIP?

Thanks,
Dong










On Mon, Jan 29, 2018 at 10:18 AM, Colin McCabe  wrote:

> On Fri, Jan 26, 2018, at 12:17, Dong Lin wrote:
> > Hey Colin,
> >
> >
> > On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe 
> wrote:
> >
> > > On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> > > > Hey Colin,
> > > >
> > > > Thanks for the comment.
> > > >
> > > > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
> > > wrote:
> > > >
> > > > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > > > > > Hey Colin,
> > > > > >
> > > > > > Thanks for reviewing the KIP.
> > > > > >
> > > > > > If I understand you right, you maybe suggesting that we can use a
> > > global
> > > > > > metadataEpoch that is incremented every time controller updates
> > > metadata.
> > > > > > The problem with this solution is that, if a topic is deleted and
> > > created
> > > > > > again, user will not know whether that the offset which is stored
> > > before
> > > > > > the topic deletion is no longer valid. This motivates the idea to
> > > include
> > > > > > per-partition partitionEpoch. Does this sound reasonable?
> > > > >
> > > > > Hi Dong,
> > > > >
> > > > > Perhaps we can store the last valid offset of each deleted topic in
> > > > > ZooKeeper.  Then, when a topic with one of those names gets
> > > re-created, we
> > > > > can start the topic at the previous end offset rather than at 0.
> This
> > > > > preserves immutability.  It is no more burdensome than having to
> > > preserve a
> > > > > "last epoch" for the deleted partition somewhere, right?
> > > > >
> > > >
> > > > My concern with this solution is that the number of zookeeper nodes
> get
> > > > more and more over time if some users keep deleting and creating
> topics.
> > > Do
> > > > you think this can be a problem?
> > >
> > > Hi Dong,
> > >
> > > We could expire the "partition tombstones" after an hour or so.  In
> > > practice this would solve the issue for clients that like to destroy
> and
> > > re-create topics all the time.  In any case, doesn't the current
> proposal
> > > add per-partition znodes as well that we have to track even after the
> > > partition is deleted?  Or did I misunderstand that?
> > >
> >
> > Actually the current KIP does not add per-partition znodes. Could you
> > double check? I can fix the KIP wiki if there is anything misleading.
>
> Hi Dong,
>
> I double-checked the KIP, and I can see that you are in fact using a
> global counter for initializing partition epochs.  So, you are correct, it
> doesn't add per-partition znodes for partitions that no longer exist.
>
> >
> > If we expire the "partition tomstones" after an hour, and the topic is
> > re-created after more than an hour since the topic deletion, then we are
> > back to the situation where user can not tell whether the topic has been
> > re-created or not, right?
>
> Yes, with an expiration period, it would not ensure immutability-- you
> could effectively reuse partition names and they would look the same.
>
> >
> >
> > >
> > > It's not really clear to me what should happen when a topic is
> destroyed
> > > and re-created with new data.  Should consumers continue to be able to
> > > consume?  We don't know where they stopped consuming from the previous
> > > incarnation of the topic, so messages may have been lost.  Certainly
> > > consuming data from offset X of the new incarnation of the topic may
> give
> > > something totally different from what you would have gotten from
> offset X
> > > of the previous incarnation of the topic.
> > >
> >
> > With the current KIP, if a consumer consumes a topic based on the last
> > remembered (offset, partitionEpoch, leaderEpoch), and if the topic is
> > re-created, consume will throw InvalidPartitionEpochException because the
> > previous partitionEpoch will be different from the current
> partitionEpoch.
> > This is described in the Proposed Changes -> Consumption after topic
> > deletion in the KIP. I can improve the KIP if there is anything not
> 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

On Fri, Jan 26, 2018, at 12:17, Dong Lin wrote:
> Hey Colin,
> 
> 
> On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe  wrote:
> 
> > On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> > > Hey Colin,
> > >
> > > Thanks for the comment.
> > >
> > > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
> > wrote:
> > >
> > > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > > > > Hey Colin,
> > > > >
> > > > > Thanks for reviewing the KIP.
> > > > >
> > > > > If I understand you right, you maybe suggesting that we can use a
> > global
> > > > > metadataEpoch that is incremented every time controller updates
> > metadata.
> > > > > The problem with this solution is that, if a topic is deleted and
> > created
> > > > > again, user will not know whether that the offset which is stored
> > before
> > > > > the topic deletion is no longer valid. This motivates the idea to
> > include
> > > > > per-partition partitionEpoch. Does this sound reasonable?
> > > >
> > > > Hi Dong,
> > > >
> > > > Perhaps we can store the last valid offset of each deleted topic in
> > > > ZooKeeper.  Then, when a topic with one of those names gets
> > re-created, we
> > > > can start the topic at the previous end offset rather than at 0.  This
> > > > preserves immutability.  It is no more burdensome than having to
> > preserve a
> > > > "last epoch" for the deleted partition somewhere, right?
> > > >
> > >
> > > My concern with this solution is that the number of zookeeper nodes get
> > > more and more over time if some users keep deleting and creating topics.
> > Do
> > > you think this can be a problem?
> >
> > Hi Dong,
> >
> > We could expire the "partition tombstones" after an hour or so.  In
> > practice this would solve the issue for clients that like to destroy and
> > re-create topics all the time.  In any case, doesn't the current proposal
> > add per-partition znodes as well that we have to track even after the
> > partition is deleted?  Or did I misunderstand that?
> >
> 
> Actually the current KIP does not add per-partition znodes. Could you
> double check? I can fix the KIP wiki if there is anything misleading.

Hi Dong,

I double-checked the KIP, and I can see that you are in fact using a global 
counter for initializing partition epochs.  So, you are correct, it doesn't add 
per-partition znodes for partitions that no longer exist.

> 
> If we expire the "partition tomstones" after an hour, and the topic is
> re-created after more than an hour since the topic deletion, then we are
> back to the situation where user can not tell whether the topic has been
> re-created or not, right?

Yes, with an expiration period, it would not ensure immutability-- you could 
effectively reuse partition names and they would look the same.

> 
> 
> >
> > It's not really clear to me what should happen when a topic is destroyed
> > and re-created with new data.  Should consumers continue to be able to
> > consume?  We don't know where they stopped consuming from the previous
> > incarnation of the topic, so messages may have been lost.  Certainly
> > consuming data from offset X of the new incarnation of the topic may give
> > something totally different from what you would have gotten from offset X
> > of the previous incarnation of the topic.
> >
> 
> With the current KIP, if a consumer consumes a topic based on the last
> remembered (offset, partitionEpoch, leaderEpoch), and if the topic is
> re-created, consume will throw InvalidPartitionEpochException because the
> previous partitionEpoch will be different from the current partitionEpoch.
> This is described in the Proposed Changes -> Consumption after topic
> deletion in the KIP. I can improve the KIP if there is anything not clear.

Thanks for the clarification.  It sounds like what you really want is 
immutability-- i.e., to never "really" reuse partition identifiers.  And you do 
this by making the partition name no longer the "real" identifier.

My big concern about this KIP is that it seems like an anti-scalability 
feature.  Now we are adding 4 extra bytes for every partition in the 
FetchResponse and Request, for example.  That could be 40 kb per request, if 
the user has 10,000 partitions.  And of course, the KIP also makes massive 
changes to UpdateMetadataRequest, MetadataResponse, OffsetCommitRequest, 
OffsetFetchResponse, LeaderAndIsrRequest, ListOffsetResponse, etc. which will 
also increase their size on the wire and in memory.

One thing that we talked a lot about in the past is replacing partition names 
with IDs.  IDs have a lot of really nice features.  They take up much less 
space in memory than strings (especially 2-byte Java strings).  They can often 
be allocated on the stack rather than the heap (important when you are dealing 
with hundreds of thousands of them).  They can be efficiently deserialized and 
serialized.  If we use 64-bit ones, we will never run out of IDs, which means 
that they can always be unique per 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Jun Rao]

Just some clarification on the current fencing logic. Currently, if the
producer uses acks=-1, a write will only succeed if the write is received
by all in-sync replicas (i.e., committed). This is true even when min.isr
is set since we first wait for a message to be committed and then check the
min.isr requirement. KIP-250 may change that, but we can discuss the
implication there. In the case where you have 3 replicas A, B and C, and A
and B are partitioned off and C becomes the new leader, the old leader A
can't commit new messages with the current ISR of {A, B, C} since C won't
be fetching from A. A will then try to persist the reduced ISR of just A
and B to ZK. This will fail since the ZK version is outdated. Then, no new
message can be committed by A. This is how we fence off the writer.

Currently, there is no fencing for the readers. We can potentially fence
off the reads in the old leader A after a timeout. However, we still need
to decide what to do within the timeout, especially when A is presented
with an offset that's larger than it's last offset.

Thanks,

Jun

On Fri, Jan 26, 2018 at 12:17 PM, Dong Lin  wrote:

> Hey Colin,
>
>
> On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe  wrote:
>
> > On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> > > Hey Colin,
> > >
> > > Thanks for the comment.
> > >
> > > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
> > wrote:
> > >
> > > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > > > > Hey Colin,
> > > > >
> > > > > Thanks for reviewing the KIP.
> > > > >
> > > > > If I understand you right, you maybe suggesting that we can use a
> > global
> > > > > metadataEpoch that is incremented every time controller updates
> > metadata.
> > > > > The problem with this solution is that, if a topic is deleted and
> > created
> > > > > again, user will not know whether that the offset which is stored
> > before
> > > > > the topic deletion is no longer valid. This motivates the idea to
> > include
> > > > > per-partition partitionEpoch. Does this sound reasonable?
> > > >
> > > > Hi Dong,
> > > >
> > > > Perhaps we can store the last valid offset of each deleted topic in
> > > > ZooKeeper.  Then, when a topic with one of those names gets
> > re-created, we
> > > > can start the topic at the previous end offset rather than at 0.
> This
> > > > preserves immutability.  It is no more burdensome than having to
> > preserve a
> > > > "last epoch" for the deleted partition somewhere, right?
> > > >
> > >
> > > My concern with this solution is that the number of zookeeper nodes get
> > > more and more over time if some users keep deleting and creating
> topics.
> > Do
> > > you think this can be a problem?
> >
> > Hi Dong,
> >
> > We could expire the "partition tombstones" after an hour or so.  In
> > practice this would solve the issue for clients that like to destroy and
> > re-create topics all the time.  In any case, doesn't the current proposal
> > add per-partition znodes as well that we have to track even after the
> > partition is deleted?  Or did I misunderstand that?
> >
>
> Actually the current KIP does not add per-partition znodes. Could you
> double check? I can fix the KIP wiki if there is anything misleading.
>
> If we expire the "partition tomstones" after an hour, and the topic is
> re-created after more than an hour since the topic deletion, then we are
> back to the situation where user can not tell whether the topic has been
> re-created or not, right?
>
>
> >
> > It's not really clear to me what should happen when a topic is destroyed
> > and re-created with new data.  Should consumers continue to be able to
> > consume?  We don't know where they stopped consuming from the previous
> > incarnation of the topic, so messages may have been lost.  Certainly
> > consuming data from offset X of the new incarnation of the topic may give
> > something totally different from what you would have gotten from offset X
> > of the previous incarnation of the topic.
> >
>
> With the current KIP, if a consumer consumes a topic based on the last
> remembered (offset, partitionEpoch, leaderEpoch), and if the topic is
> re-created, consume will throw InvalidPartitionEpochException because the
> previous partitionEpoch will be different from the current partitionEpoch.
> This is described in the Proposed Changes -> Consumption after topic
> deletion in the KIP. I can improve the KIP if there is anything not clear.
>
>
> > By choosing to reuse the same (topic, partition, offset) 3-tuple, we have
>
> chosen to give up immutability.  That was a really bad decision.  And now
> > we have to worry about time dependencies, stale cached data, and all the
> > rest.  We can't completely fix this inside Kafka no matter what we do,
> > because not all that cached data is inside Kafka itself.  Some of it may
> be
> > in systems that Kafka has sent data to, such as other daemons, SQL
> > databases, streams, and so forth.
> 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Colin,


On Fri, Jan 26, 2018 at 10:16 AM, Colin McCabe  wrote:

> On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> > Hey Colin,
> >
> > Thanks for the comment.
> >
> > On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe 
> wrote:
> >
> > > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > > > Hey Colin,
> > > >
> > > > Thanks for reviewing the KIP.
> > > >
> > > > If I understand you right, you maybe suggesting that we can use a
> global
> > > > metadataEpoch that is incremented every time controller updates
> metadata.
> > > > The problem with this solution is that, if a topic is deleted and
> created
> > > > again, user will not know whether that the offset which is stored
> before
> > > > the topic deletion is no longer valid. This motivates the idea to
> include
> > > > per-partition partitionEpoch. Does this sound reasonable?
> > >
> > > Hi Dong,
> > >
> > > Perhaps we can store the last valid offset of each deleted topic in
> > > ZooKeeper.  Then, when a topic with one of those names gets
> re-created, we
> > > can start the topic at the previous end offset rather than at 0.  This
> > > preserves immutability.  It is no more burdensome than having to
> preserve a
> > > "last epoch" for the deleted partition somewhere, right?
> > >
> >
> > My concern with this solution is that the number of zookeeper nodes get
> > more and more over time if some users keep deleting and creating topics.
> Do
> > you think this can be a problem?
>
> Hi Dong,
>
> We could expire the "partition tombstones" after an hour or so.  In
> practice this would solve the issue for clients that like to destroy and
> re-create topics all the time.  In any case, doesn't the current proposal
> add per-partition znodes as well that we have to track even after the
> partition is deleted?  Or did I misunderstand that?
>

Actually the current KIP does not add per-partition znodes. Could you
double check? I can fix the KIP wiki if there is anything misleading.

If we expire the "partition tomstones" after an hour, and the topic is
re-created after more than an hour since the topic deletion, then we are
back to the situation where user can not tell whether the topic has been
re-created or not, right?


>
> It's not really clear to me what should happen when a topic is destroyed
> and re-created with new data.  Should consumers continue to be able to
> consume?  We don't know where they stopped consuming from the previous
> incarnation of the topic, so messages may have been lost.  Certainly
> consuming data from offset X of the new incarnation of the topic may give
> something totally different from what you would have gotten from offset X
> of the previous incarnation of the topic.
>

With the current KIP, if a consumer consumes a topic based on the last
remembered (offset, partitionEpoch, leaderEpoch), and if the topic is
re-created, consume will throw InvalidPartitionEpochException because the
previous partitionEpoch will be different from the current partitionEpoch.
This is described in the Proposed Changes -> Consumption after topic
deletion in the KIP. I can improve the KIP if there is anything not clear.


> By choosing to reuse the same (topic, partition, offset) 3-tuple, we have

chosen to give up immutability.  That was a really bad decision.  And now
> we have to worry about time dependencies, stale cached data, and all the
> rest.  We can't completely fix this inside Kafka no matter what we do,
> because not all that cached data is inside Kafka itself.  Some of it may be
> in systems that Kafka has sent data to, such as other daemons, SQL
> databases, streams, and so forth.
>

The current KIP will uniquely identify a message using (topic, partition,
offset, partitionEpoch) 4-tuple. This addresses the message immutability
issue that you mentioned. Is there any corner case where the message
immutability is still not preserved with the current KIP?


>
> I guess the idea here is that mirror maker should work as expected when
> users destroy a topic and re-create it with the same name.  That's kind of
> tough, though, since in that scenario, mirror maker probably should destroy
> and re-create the topic on the other end, too, right?  Otherwise, what you
> end up with on the other end could be half of one incarnation of the topic,
> and half of another.
>
> What mirror maker really needs is to be able to follow a stream of events
> about the kafka cluster itself.  We could have some master topic which is
> always present and which contains data about all topic deletions,
> creations, etc.  Then MM can simply follow this topic and do what is needed.
>
> >
> >
> > >
> > > >
> > > > Then the next question maybe, should we use a global metadataEpoch +
> > > > per-partition partitionEpoch, instead of using per-partition
> leaderEpoch
> > > +
> > > > per-partition leaderEpoch. The former solution using metadataEpoch
> would
> > > > not work due to the following scenario (provided by Jun):
> > > >

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

On Thu, Jan 25, 2018, at 16:47, Dong Lin wrote:
> Hey Colin,
> 
> Thanks for the comment.
> 
> On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe  wrote:
> 
> > On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > > Hey Colin,
> > >
> > > Thanks for reviewing the KIP.
> > >
> > > If I understand you right, you maybe suggesting that we can use a global
> > > metadataEpoch that is incremented every time controller updates metadata.
> > > The problem with this solution is that, if a topic is deleted and created
> > > again, user will not know whether that the offset which is stored before
> > > the topic deletion is no longer valid. This motivates the idea to include
> > > per-partition partitionEpoch. Does this sound reasonable?
> >
> > Hi Dong,
> >
> > Perhaps we can store the last valid offset of each deleted topic in
> > ZooKeeper.  Then, when a topic with one of those names gets re-created, we
> > can start the topic at the previous end offset rather than at 0.  This
> > preserves immutability.  It is no more burdensome than having to preserve a
> > "last epoch" for the deleted partition somewhere, right?
> >
> 
> My concern with this solution is that the number of zookeeper nodes get
> more and more over time if some users keep deleting and creating topics. Do
> you think this can be a problem?

Hi Dong,

We could expire the "partition tombstones" after an hour or so.  In practice 
this would solve the issue for clients that like to destroy and re-create 
topics all the time.  In any case, doesn't the current proposal add 
per-partition znodes as well that we have to track even after the partition is 
deleted?  Or did I misunderstand that?  

It's not really clear to me what should happen when a topic is destroyed and 
re-created with new data.  Should consumers continue to be able to consume?  We 
don't know where they stopped consuming from the previous incarnation of the 
topic, so messages may have been lost.  Certainly consuming data from offset X 
of the new incarnation of the topic may give something totally different from 
what you would have gotten from offset X of the previous incarnation of the 
topic.

By choosing to reuse the same (topic, partition, offset) 3-tuple, we have 
chosen to give up immutability.  That was a really bad decision.  And now we 
have to worry about time dependencies, stale cached data, and all the rest.  We 
can't completely fix this inside Kafka no matter what we do, because not all 
that cached data is inside Kafka itself.  Some of it may be in systems that 
Kafka has sent data to, such as other daemons, SQL databases, streams, and so 
forth.

I guess the idea here is that mirror maker should work as expected when users 
destroy a topic and re-create it with the same name.  That's kind of tough, 
though, since in that scenario, mirror maker probably should destroy and 
re-create the topic on the other end, too, right?  Otherwise, what you end up 
with on the other end could be half of one incarnation of the topic, and half 
of another.

What mirror maker really needs is to be able to follow a stream of events about 
the kafka cluster itself.  We could have some master topic which is always 
present and which contains data about all topic deletions, creations, etc.  
Then MM can simply follow this topic and do what is needed.

> 
> 
> >
> > >
> > > Then the next question maybe, should we use a global metadataEpoch +
> > > per-partition partitionEpoch, instead of using per-partition leaderEpoch
> > +
> > > per-partition leaderEpoch. The former solution using metadataEpoch would
> > > not work due to the following scenario (provided by Jun):
> > >
> > > "Consider the following scenario. In metadata v1, the leader for a
> > > partition is at broker 1. In metadata v2, leader is at broker 2. In
> > > metadata v3, leader is at broker 1 again. The last committed offset in
> > v1,
> > > v2 and v3 are 10, 20 and 30, respectively. A consumer is started and
> > reads
> > > metadata v1 and reads messages from offset 0 to 25 from broker 1. My
> > > understanding is that in the current proposal, the metadata version
> > > associated with offset 25 is v1. The consumer is then restarted and
> > fetches
> > > metadata v2. The consumer tries to read from broker 2, which is the old
> > > leader with the last offset at 20. In this case, the consumer will still
> > > get OffsetOutOfRangeException incorrectly."
> > >
> > > Regarding your comment "For the second purpose, this is "soft state"
> > > anyway.  If the client thinks X is the leader but Y is really the leader,
> > > the client will talk to X, and X will point out its mistake by sending
> > back
> > > a NOT_LEADER_FOR_PARTITION.", it is probably no true. The problem here is
> > > that the old leader X may still think it is the leader of the partition
> > and
> > > thus it will not send back NOT_LEADER_FOR_PARTITION. The reason is
> > provided
> > > in KAFKA-6262. Can you check if that makes sense?
> >
> > This is 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Colin,

Thanks for the comment.

On Thu, Jan 25, 2018 at 4:15 PM, Colin McCabe  wrote:

> On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> > Hey Colin,
> >
> > Thanks for reviewing the KIP.
> >
> > If I understand you right, you maybe suggesting that we can use a global
> > metadataEpoch that is incremented every time controller updates metadata.
> > The problem with this solution is that, if a topic is deleted and created
> > again, user will not know whether that the offset which is stored before
> > the topic deletion is no longer valid. This motivates the idea to include
> > per-partition partitionEpoch. Does this sound reasonable?
>
> Hi Dong,
>
> Perhaps we can store the last valid offset of each deleted topic in
> ZooKeeper.  Then, when a topic with one of those names gets re-created, we
> can start the topic at the previous end offset rather than at 0.  This
> preserves immutability.  It is no more burdensome than having to preserve a
> "last epoch" for the deleted partition somewhere, right?
>

My concern with this solution is that the number of zookeeper nodes get
more and more over time if some users keep deleting and creating topics. Do
you think this can be a problem?


>
> >
> > Then the next question maybe, should we use a global metadataEpoch +
> > per-partition partitionEpoch, instead of using per-partition leaderEpoch
> +
> > per-partition leaderEpoch. The former solution using metadataEpoch would
> > not work due to the following scenario (provided by Jun):
> >
> > "Consider the following scenario. In metadata v1, the leader for a
> > partition is at broker 1. In metadata v2, leader is at broker 2. In
> > metadata v3, leader is at broker 1 again. The last committed offset in
> v1,
> > v2 and v3 are 10, 20 and 30, respectively. A consumer is started and
> reads
> > metadata v1 and reads messages from offset 0 to 25 from broker 1. My
> > understanding is that in the current proposal, the metadata version
> > associated with offset 25 is v1. The consumer is then restarted and
> fetches
> > metadata v2. The consumer tries to read from broker 2, which is the old
> > leader with the last offset at 20. In this case, the consumer will still
> > get OffsetOutOfRangeException incorrectly."
> >
> > Regarding your comment "For the second purpose, this is "soft state"
> > anyway.  If the client thinks X is the leader but Y is really the leader,
> > the client will talk to X, and X will point out its mistake by sending
> back
> > a NOT_LEADER_FOR_PARTITION.", it is probably no true. The problem here is
> > that the old leader X may still think it is the leader of the partition
> and
> > thus it will not send back NOT_LEADER_FOR_PARTITION. The reason is
> provided
> > in KAFKA-6262. Can you check if that makes sense?
>
> This is solvable with a timeout, right?  If the leader can't communicate
> with the controller for a certain period of time, it should stop acting as
> the leader.  We have to solve this problem, anyway, in order to fix all the
> corner cases.
>

Not sure if I fully understand your proposal. The proposal seems to require
non-trivial changes to our existing leadership election mechanism. Could
you provide more detail regarding how it works? For example, how should
user choose this timeout, how leader determines whether it can still
communicate with controller, and how this triggers controller to elect new
leader?


> best,
> Colin
>
> >
> > Regards,
> > Dong
> >
> >
> > On Wed, Jan 24, 2018 at 10:39 AM, Colin McCabe 
> wrote:
> >
> > > Hi Dong,
> > >
> > > Thanks for proposing this KIP.  I think a metadata epoch is a really
> good
> > > idea.
> > >
> > > I read through the DISCUSS thread, but I still don't have a clear
> picture
> > > of why the proposal uses a metadata epoch per partition rather than a
> > > global metadata epoch.  A metadata epoch per partition is kind of
> > > unpleasant-- it's at least 4 extra bytes per partition that we have to
> send
> > > over the wire in every full metadata request, which could become extra
> > > kilobytes on the wire when the number of partitions becomes large.
> Plus,
> > > we have to update all the auxillary classes to include an epoch.
> > >
> > > We need to have a global metadata epoch anyway to handle partition
> > > addition and deletion.  For example, if I give you
> > > MetadataResponse{part1,epoch 1, part2, epoch 1} and {part1, epoch1},
> which
> > > MetadataResponse is newer?  You have no way of knowing.  It could be
> that
> > > part2 has just been created, and the response with 2 partitions is
> newer.
> > > Or it coudl be that part2 has just been deleted, and therefore the
> response
> > > with 1 partition is newer.  You must have a global epoch to
> disambiguate
> > > these two cases.
> > >
> > > Previously, I worked on the Ceph distributed filesystem.  Ceph had the
> > > concept of a map of the whole cluster, maintained by a few servers
> doing
> > > paxos.  This map was versioned by 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

On Wed, Jan 24, 2018, at 21:07, Dong Lin wrote:
> Hey Colin,
> 
> Thanks for reviewing the KIP.
> 
> If I understand you right, you maybe suggesting that we can use a global
> metadataEpoch that is incremented every time controller updates metadata.
> The problem with this solution is that, if a topic is deleted and created
> again, user will not know whether that the offset which is stored before
> the topic deletion is no longer valid. This motivates the idea to include
> per-partition partitionEpoch. Does this sound reasonable?

Hi Dong,

Perhaps we can store the last valid offset of each deleted topic in ZooKeeper.  
Then, when a topic with one of those names gets re-created, we can start the 
topic at the previous end offset rather than at 0.  This preserves 
immutability.  It is no more burdensome than having to preserve a "last epoch" 
for the deleted partition somewhere, right?

> 
> Then the next question maybe, should we use a global metadataEpoch +
> per-partition partitionEpoch, instead of using per-partition leaderEpoch +
> per-partition leaderEpoch. The former solution using metadataEpoch would
> not work due to the following scenario (provided by Jun):
> 
> "Consider the following scenario. In metadata v1, the leader for a
> partition is at broker 1. In metadata v2, leader is at broker 2. In
> metadata v3, leader is at broker 1 again. The last committed offset in v1,
> v2 and v3 are 10, 20 and 30, respectively. A consumer is started and reads
> metadata v1 and reads messages from offset 0 to 25 from broker 1. My
> understanding is that in the current proposal, the metadata version
> associated with offset 25 is v1. The consumer is then restarted and fetches
> metadata v2. The consumer tries to read from broker 2, which is the old
> leader with the last offset at 20. In this case, the consumer will still
> get OffsetOutOfRangeException incorrectly."
> 
> Regarding your comment "For the second purpose, this is "soft state"
> anyway.  If the client thinks X is the leader but Y is really the leader,
> the client will talk to X, and X will point out its mistake by sending back
> a NOT_LEADER_FOR_PARTITION.", it is probably no true. The problem here is
> that the old leader X may still think it is the leader of the partition and
> thus it will not send back NOT_LEADER_FOR_PARTITION. The reason is provided
> in KAFKA-6262. Can you check if that makes sense?

This is solvable with a timeout, right?  If the leader can't communicate with 
the controller for a certain period of time, it should stop acting as the 
leader.  We have to solve this problem, anyway, in order to fix all the corner 
cases.

best,
Colin

> 
> Regards,
> Dong
> 
> 
> On Wed, Jan 24, 2018 at 10:39 AM, Colin McCabe  wrote:
> 
> > Hi Dong,
> >
> > Thanks for proposing this KIP.  I think a metadata epoch is a really good
> > idea.
> >
> > I read through the DISCUSS thread, but I still don't have a clear picture
> > of why the proposal uses a metadata epoch per partition rather than a
> > global metadata epoch.  A metadata epoch per partition is kind of
> > unpleasant-- it's at least 4 extra bytes per partition that we have to send
> > over the wire in every full metadata request, which could become extra
> > kilobytes on the wire when the number of partitions becomes large.  Plus,
> > we have to update all the auxillary classes to include an epoch.
> >
> > We need to have a global metadata epoch anyway to handle partition
> > addition and deletion.  For example, if I give you
> > MetadataResponse{part1,epoch 1, part2, epoch 1} and {part1, epoch1}, which
> > MetadataResponse is newer?  You have no way of knowing.  It could be that
> > part2 has just been created, and the response with 2 partitions is newer.
> > Or it coudl be that part2 has just been deleted, and therefore the response
> > with 1 partition is newer.  You must have a global epoch to disambiguate
> > these two cases.
> >
> > Previously, I worked on the Ceph distributed filesystem.  Ceph had the
> > concept of a map of the whole cluster, maintained by a few servers doing
> > paxos.  This map was versioned by a single 64-bit epoch number which
> > increased on every change.  It was propagated to clients through gossip.  I
> > wonder if something similar could work here?
> >
> > It seems like the the Kafka MetadataResponse serves two somewhat unrelated
> > purposes.  Firstly, it lets clients know what partitions exist in the
> > system and where they live.  Secondly, it lets clients know which nodes
> > within the partition are in-sync (in the ISR) and which node is the leader.
> >
> > The first purpose is what you really need a metadata epoch for, I think.
> > You want to know whether a partition exists or not, or you want to know
> > which nodes you should talk to in order to write to a given partition.  A
> > single metadata epoch for the whole response should be adequate here.  We
> > should not change the partition assignment without going 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Colin,

Thanks for reviewing the KIP.

If I understand you right, you maybe suggesting that we can use a global
metadataEpoch that is incremented every time controller updates metadata.
The problem with this solution is that, if a topic is deleted and created
again, user will not know whether that the offset which is stored before
the topic deletion is no longer valid. This motivates the idea to include
per-partition partitionEpoch. Does this sound reasonable?

Then the next question maybe, should we use a global metadataEpoch +
per-partition partitionEpoch, instead of using per-partition leaderEpoch +
per-partition leaderEpoch. The former solution using metadataEpoch would
not work due to the following scenario (provided by Jun):

"Consider the following scenario. In metadata v1, the leader for a
partition is at broker 1. In metadata v2, leader is at broker 2. In
metadata v3, leader is at broker 1 again. The last committed offset in v1,
v2 and v3 are 10, 20 and 30, respectively. A consumer is started and reads
metadata v1 and reads messages from offset 0 to 25 from broker 1. My
understanding is that in the current proposal, the metadata version
associated with offset 25 is v1. The consumer is then restarted and fetches
metadata v2. The consumer tries to read from broker 2, which is the old
leader with the last offset at 20. In this case, the consumer will still
get OffsetOutOfRangeException incorrectly."

Regarding your comment "For the second purpose, this is "soft state"
anyway.  If the client thinks X is the leader but Y is really the leader,
the client will talk to X, and X will point out its mistake by sending back
a NOT_LEADER_FOR_PARTITION.", it is probably no true. The problem here is
that the old leader X may still think it is the leader of the partition and
thus it will not send back NOT_LEADER_FOR_PARTITION. The reason is provided
in KAFKA-6262. Can you check if that makes sense?

Regards,
Dong


On Wed, Jan 24, 2018 at 10:39 AM, Colin McCabe  wrote:

> Hi Dong,
>
> Thanks for proposing this KIP.  I think a metadata epoch is a really good
> idea.
>
> I read through the DISCUSS thread, but I still don't have a clear picture
> of why the proposal uses a metadata epoch per partition rather than a
> global metadata epoch.  A metadata epoch per partition is kind of
> unpleasant-- it's at least 4 extra bytes per partition that we have to send
> over the wire in every full metadata request, which could become extra
> kilobytes on the wire when the number of partitions becomes large.  Plus,
> we have to update all the auxillary classes to include an epoch.
>
> We need to have a global metadata epoch anyway to handle partition
> addition and deletion.  For example, if I give you
> MetadataResponse{part1,epoch 1, part2, epoch 1} and {part1, epoch1}, which
> MetadataResponse is newer?  You have no way of knowing.  It could be that
> part2 has just been created, and the response with 2 partitions is newer.
> Or it coudl be that part2 has just been deleted, and therefore the response
> with 1 partition is newer.  You must have a global epoch to disambiguate
> these two cases.
>
> Previously, I worked on the Ceph distributed filesystem.  Ceph had the
> concept of a map of the whole cluster, maintained by a few servers doing
> paxos.  This map was versioned by a single 64-bit epoch number which
> increased on every change.  It was propagated to clients through gossip.  I
> wonder if something similar could work here?
>
> It seems like the the Kafka MetadataResponse serves two somewhat unrelated
> purposes.  Firstly, it lets clients know what partitions exist in the
> system and where they live.  Secondly, it lets clients know which nodes
> within the partition are in-sync (in the ISR) and which node is the leader.
>
> The first purpose is what you really need a metadata epoch for, I think.
> You want to know whether a partition exists or not, or you want to know
> which nodes you should talk to in order to write to a given partition.  A
> single metadata epoch for the whole response should be adequate here.  We
> should not change the partition assignment without going through zookeeper
> (or a similar system), and this inherently serializes updates into a
> numbered stream.  Brokers should also stop responding to requests when they
> are unable to contact ZK for a certain time period.  This prevents the case
> where a given partition has been moved off some set of nodes, but a client
> still ends up talking to those nodes and writing data there.
>
> For the second purpose, this is "soft state" anyway.  If the client thinks
> X is the leader but Y is really the leader, the client will talk to X, and
> X will point out its mistake by sending back a NOT_LEADER_FOR_PARTITION.
> Then the client can update its metadata again and find the new leader, if
> there is one.  There is no need for an epoch to handle this.  Similarly, I
> can't think of a reason why changing the in-sync replica set 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Colin McCabe]

Hi Dong,

Thanks for proposing this KIP.  I think a metadata epoch is a really good idea.

I read through the DISCUSS thread, but I still don't have a clear picture of 
why the proposal uses a metadata epoch per partition rather than a global 
metadata epoch.  A metadata epoch per partition is kind of unpleasant-- it's at 
least 4 extra bytes per partition that we have to send over the wire in every 
full metadata request, which could become extra kilobytes on the wire when the 
number of partitions becomes large.  Plus, we have to update all the auxillary 
classes to include an epoch.

We need to have a global metadata epoch anyway to handle partition addition and 
deletion.  For example, if I give you MetadataResponse{part1,epoch 1, part2, 
epoch 1} and {part1, epoch1}, which MetadataResponse is newer?  You have no way 
of knowing.  It could be that part2 has just been created, and the response 
with 2 partitions is newer.  Or it coudl be that part2 has just been deleted, 
and therefore the response with 1 partition is newer.  You must have a global 
epoch to disambiguate these two cases.

Previously, I worked on the Ceph distributed filesystem.  Ceph had the concept 
of a map of the whole cluster, maintained by a few servers doing paxos.  This 
map was versioned by a single 64-bit epoch number which increased on every 
change.  It was propagated to clients through gossip.  I wonder if something 
similar could work here?

It seems like the the Kafka MetadataResponse serves two somewhat unrelated 
purposes.  Firstly, it lets clients know what partitions exist in the system 
and where they live.  Secondly, it lets clients know which nodes within the 
partition are in-sync (in the ISR) and which node is the leader.

The first purpose is what you really need a metadata epoch for, I think.  You 
want to know whether a partition exists or not, or you want to know which nodes 
you should talk to in order to write to a given partition.  A single metadata 
epoch for the whole response should be adequate here.  We should not change the 
partition assignment without going through zookeeper (or a similar system), and 
this inherently serializes updates into a numbered stream.  Brokers should also 
stop responding to requests when they are unable to contact ZK for a certain 
time period.  This prevents the case where a given partition has been moved off 
some set of nodes, but a client still ends up talking to those nodes and 
writing data there.

For the second purpose, this is "soft state" anyway.  If the client thinks X is 
the leader but Y is really the leader, the client will talk to X, and X will 
point out its mistake by sending back a NOT_LEADER_FOR_PARTITION.  Then the 
client can update its metadata again and find the new leader, if there is one.  
There is no need for an epoch to handle this.  Similarly, I can't think of a 
reason why changing the in-sync replica set needs to bump the epoch.

best,
Colin


On Wed, Jan 24, 2018, at 09:45, Dong Lin wrote:
> Thanks much for reviewing the KIP!
> 
> Dong
> 
> On Wed, Jan 24, 2018 at 7:10 AM, Guozhang Wang  wrote:
> 
> > Yeah that makes sense, again I'm just making sure we understand all the
> > scenarios and what to expect.
> >
> > I agree that if, more generally speaking, say users have only consumed to
> > offset 8, and then call seek(16) to "jump" to a further position, then she
> > needs to be aware that OORE maybe thrown and she needs to handle it or rely
> > on reset policy which should not surprise her.
> >
> >
> > I'm +1 on the KIP.
> >
> > Guozhang
> >
> >
> > On Wed, Jan 24, 2018 at 12:31 AM, Dong Lin  wrote:
> >
> > > Yes, in general we can not prevent OffsetOutOfRangeException if user
> > seeks
> > > to a wrong offset. The main goal is to prevent OffsetOutOfRangeException
> > if
> > > user has done things in the right way, e.g. user should know that there
> > is
> > > message with this offset.
> > >
> > > For example, if user calls seek(..) right after construction, the only
> > > reason I can think of is that user stores offset externally. In this
> > case,
> > > user currently needs to use the offset which is obtained using
> > position(..)
> > > from the last run. With this KIP, user needs to get the offset and the
> > > offsetEpoch using positionAndOffsetEpoch(...) and stores these
> > information
> > > externally. The next time user starts consumer, he/she needs to call
> > > seek(..., offset, offsetEpoch) right after construction. Then KIP should
> > be
> > > able to ensure that we don't throw OffsetOutOfRangeException if there is
> > no
> > > unclean leader election.
> > >
> > > Does this sound OK?
> > >
> > > Regards,
> > > Dong
> > >
> > >
> > > On Tue, Jan 23, 2018 at 11:44 PM, Guozhang Wang 
> > > wrote:
> > >
> > > > "If consumer wants to consume message with offset 16, then consumer
> > must
> > > > have
> > > > already fetched message with offset 15"
> > > >
> > > > --> this 

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Thanks much for reviewing the KIP!

Dong

On Wed, Jan 24, 2018 at 7:10 AM, Guozhang Wang  wrote:

> Yeah that makes sense, again I'm just making sure we understand all the
> scenarios and what to expect.
>
> I agree that if, more generally speaking, say users have only consumed to
> offset 8, and then call seek(16) to "jump" to a further position, then she
> needs to be aware that OORE maybe thrown and she needs to handle it or rely
> on reset policy which should not surprise her.
>
>
> I'm +1 on the KIP.
>
> Guozhang
>
>
> On Wed, Jan 24, 2018 at 12:31 AM, Dong Lin  wrote:
>
> > Yes, in general we can not prevent OffsetOutOfRangeException if user
> seeks
> > to a wrong offset. The main goal is to prevent OffsetOutOfRangeException
> if
> > user has done things in the right way, e.g. user should know that there
> is
> > message with this offset.
> >
> > For example, if user calls seek(..) right after construction, the only
> > reason I can think of is that user stores offset externally. In this
> case,
> > user currently needs to use the offset which is obtained using
> position(..)
> > from the last run. With this KIP, user needs to get the offset and the
> > offsetEpoch using positionAndOffsetEpoch(...) and stores these
> information
> > externally. The next time user starts consumer, he/she needs to call
> > seek(..., offset, offsetEpoch) right after construction. Then KIP should
> be
> > able to ensure that we don't throw OffsetOutOfRangeException if there is
> no
> > unclean leader election.
> >
> > Does this sound OK?
> >
> > Regards,
> > Dong
> >
> >
> > On Tue, Jan 23, 2018 at 11:44 PM, Guozhang Wang 
> > wrote:
> >
> > > "If consumer wants to consume message with offset 16, then consumer
> must
> > > have
> > > already fetched message with offset 15"
> > >
> > > --> this may not be always true right? What if consumer just call
> > seek(16)
> > > after construction and then poll without committed offset ever stored
> > > before? Admittedly it is rare but we do not programmably disallow it.
> > >
> > >
> > > Guozhang
> > >
> > > On Tue, Jan 23, 2018 at 10:42 PM, Dong Lin 
> wrote:
> > >
> > > > Hey Guozhang,
> > > >
> > > > Thanks much for reviewing the KIP!
> > > >
> > > > In the scenario you described, let's assume that broker A has
> messages
> > > with
> > > > offset up to 10, and broker B has messages with offset up to 20. If
> > > > consumer wants to consume message with offset 9, it will not receive
> > > > OffsetOutOfRangeException
> > > > from broker A.
> > > >
> > > > If consumer wants to consume message with offset 16, then consumer
> must
> > > > have already fetched message with offset 15, which can only come from
> > > > broker B. Because consumer will fetch from broker B only if
> leaderEpoch
> > > >=
> > > > 2, then the current consumer leaderEpoch can not be 1 since this KIP
> > > > prevents leaderEpoch rewind. Thus we will not have
> > > > OffsetOutOfRangeException
> > > > in this case.
> > > >
> > > > Does this address your question, or maybe there is more advanced
> > scenario
> > > > that the KIP does not handle?
> > > >
> > > > Thanks,
> > > > Dong
> > > >
> > > > On Tue, Jan 23, 2018 at 9:43 PM, Guozhang Wang 
> > > wrote:
> > > >
> > > > > Thanks Dong, I made a pass over the wiki and it lgtm.
> > > > >
> > > > > Just a quick question: can we completely eliminate the
> > > > > OffsetOutOfRangeException with this approach? Say if there is
> > > consecutive
> > > > > leader changes such that the cached metadata's partition epoch is
> 1,
> > > and
> > > > > the metadata fetch response returns  with partition epoch 2
> pointing
> > to
> > > > > leader broker A, while the actual up-to-date metadata has partition
> > > > epoch 3
> > > > > whose leader is now broker B, the metadata refresh will still
> succeed
> > > and
> > > > > the follow-up fetch request may still see OORE?
> > > > >
> > > > >
> > > > > Guozhang
> > > > >
> > > > >
> > > > > On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin 
> > wrote:
> > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > I would like to start the voting process for KIP-232:
> > > > > >
> > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > > > > > 232%3A+Detect+outdated+metadata+using+leaderEpoch+
> > and+partitionEpoch
> > > > > >
> > > > > > The KIP will help fix a concurrency issue in Kafka which
> currently
> > > can
> > > > > > cause message loss or message duplication in consumer.
> > > > > >
> > > > > > Regards,
> > > > > > Dong
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > -- Guozhang
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > -- Guozhang
> > >
> >
>
>
>
> --
> -- Guozhang
>

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Guozhang Wang]

Yeah that makes sense, again I'm just making sure we understand all the
scenarios and what to expect.

I agree that if, more generally speaking, say users have only consumed to
offset 8, and then call seek(16) to "jump" to a further position, then she
needs to be aware that OORE maybe thrown and she needs to handle it or rely
on reset policy which should not surprise her.


I'm +1 on the KIP.

Guozhang


On Wed, Jan 24, 2018 at 12:31 AM, Dong Lin  wrote:

> Yes, in general we can not prevent OffsetOutOfRangeException if user seeks
> to a wrong offset. The main goal is to prevent OffsetOutOfRangeException if
> user has done things in the right way, e.g. user should know that there is
> message with this offset.
>
> For example, if user calls seek(..) right after construction, the only
> reason I can think of is that user stores offset externally. In this case,
> user currently needs to use the offset which is obtained using position(..)
> from the last run. With this KIP, user needs to get the offset and the
> offsetEpoch using positionAndOffsetEpoch(...) and stores these information
> externally. The next time user starts consumer, he/she needs to call
> seek(..., offset, offsetEpoch) right after construction. Then KIP should be
> able to ensure that we don't throw OffsetOutOfRangeException if there is no
> unclean leader election.
>
> Does this sound OK?
>
> Regards,
> Dong
>
>
> On Tue, Jan 23, 2018 at 11:44 PM, Guozhang Wang 
> wrote:
>
> > "If consumer wants to consume message with offset 16, then consumer must
> > have
> > already fetched message with offset 15"
> >
> > --> this may not be always true right? What if consumer just call
> seek(16)
> > after construction and then poll without committed offset ever stored
> > before? Admittedly it is rare but we do not programmably disallow it.
> >
> >
> > Guozhang
> >
> > On Tue, Jan 23, 2018 at 10:42 PM, Dong Lin  wrote:
> >
> > > Hey Guozhang,
> > >
> > > Thanks much for reviewing the KIP!
> > >
> > > In the scenario you described, let's assume that broker A has messages
> > with
> > > offset up to 10, and broker B has messages with offset up to 20. If
> > > consumer wants to consume message with offset 9, it will not receive
> > > OffsetOutOfRangeException
> > > from broker A.
> > >
> > > If consumer wants to consume message with offset 16, then consumer must
> > > have already fetched message with offset 15, which can only come from
> > > broker B. Because consumer will fetch from broker B only if leaderEpoch
> > >=
> > > 2, then the current consumer leaderEpoch can not be 1 since this KIP
> > > prevents leaderEpoch rewind. Thus we will not have
> > > OffsetOutOfRangeException
> > > in this case.
> > >
> > > Does this address your question, or maybe there is more advanced
> scenario
> > > that the KIP does not handle?
> > >
> > > Thanks,
> > > Dong
> > >
> > > On Tue, Jan 23, 2018 at 9:43 PM, Guozhang Wang 
> > wrote:
> > >
> > > > Thanks Dong, I made a pass over the wiki and it lgtm.
> > > >
> > > > Just a quick question: can we completely eliminate the
> > > > OffsetOutOfRangeException with this approach? Say if there is
> > consecutive
> > > > leader changes such that the cached metadata's partition epoch is 1,
> > and
> > > > the metadata fetch response returns  with partition epoch 2 pointing
> to
> > > > leader broker A, while the actual up-to-date metadata has partition
> > > epoch 3
> > > > whose leader is now broker B, the metadata refresh will still succeed
> > and
> > > > the follow-up fetch request may still see OORE?
> > > >
> > > >
> > > > Guozhang
> > > >
> > > >
> > > > On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin 
> wrote:
> > > >
> > > > > Hi all,
> > > > >
> > > > > I would like to start the voting process for KIP-232:
> > > > >
> > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > > > > 232%3A+Detect+outdated+metadata+using+leaderEpoch+
> and+partitionEpoch
> > > > >
> > > > > The KIP will help fix a concurrency issue in Kafka which currently
> > can
> > > > > cause message loss or message duplication in consumer.
> > > > >
> > > > > Regards,
> > > > > Dong
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > -- Guozhang
> > > >
> > >
> >
> >
> >
> > --
> > -- Guozhang
> >
>



-- 
-- Guozhang

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Yes, in general we can not prevent OffsetOutOfRangeException if user seeks
to a wrong offset. The main goal is to prevent OffsetOutOfRangeException if
user has done things in the right way, e.g. user should know that there is
message with this offset.

For example, if user calls seek(..) right after construction, the only
reason I can think of is that user stores offset externally. In this case,
user currently needs to use the offset which is obtained using position(..)
from the last run. With this KIP, user needs to get the offset and the
offsetEpoch using positionAndOffsetEpoch(...) and stores these information
externally. The next time user starts consumer, he/she needs to call
seek(..., offset, offsetEpoch) right after construction. Then KIP should be
able to ensure that we don't throw OffsetOutOfRangeException if there is no
unclean leader election.

Does this sound OK?

Regards,
Dong


On Tue, Jan 23, 2018 at 11:44 PM, Guozhang Wang  wrote:

> "If consumer wants to consume message with offset 16, then consumer must
> have
> already fetched message with offset 15"
>
> --> this may not be always true right? What if consumer just call seek(16)
> after construction and then poll without committed offset ever stored
> before? Admittedly it is rare but we do not programmably disallow it.
>
>
> Guozhang
>
> On Tue, Jan 23, 2018 at 10:42 PM, Dong Lin  wrote:
>
> > Hey Guozhang,
> >
> > Thanks much for reviewing the KIP!
> >
> > In the scenario you described, let's assume that broker A has messages
> with
> > offset up to 10, and broker B has messages with offset up to 20. If
> > consumer wants to consume message with offset 9, it will not receive
> > OffsetOutOfRangeException
> > from broker A.
> >
> > If consumer wants to consume message with offset 16, then consumer must
> > have already fetched message with offset 15, which can only come from
> > broker B. Because consumer will fetch from broker B only if leaderEpoch
> >=
> > 2, then the current consumer leaderEpoch can not be 1 since this KIP
> > prevents leaderEpoch rewind. Thus we will not have
> > OffsetOutOfRangeException
> > in this case.
> >
> > Does this address your question, or maybe there is more advanced scenario
> > that the KIP does not handle?
> >
> > Thanks,
> > Dong
> >
> > On Tue, Jan 23, 2018 at 9:43 PM, Guozhang Wang 
> wrote:
> >
> > > Thanks Dong, I made a pass over the wiki and it lgtm.
> > >
> > > Just a quick question: can we completely eliminate the
> > > OffsetOutOfRangeException with this approach? Say if there is
> consecutive
> > > leader changes such that the cached metadata's partition epoch is 1,
> and
> > > the metadata fetch response returns  with partition epoch 2 pointing to
> > > leader broker A, while the actual up-to-date metadata has partition
> > epoch 3
> > > whose leader is now broker B, the metadata refresh will still succeed
> and
> > > the follow-up fetch request may still see OORE?
> > >
> > >
> > > Guozhang
> > >
> > >
> > > On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin  wrote:
> > >
> > > > Hi all,
> > > >
> > > > I would like to start the voting process for KIP-232:
> > > >
> > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > > > 232%3A+Detect+outdated+metadata+using+leaderEpoch+and+partitionEpoch
> > > >
> > > > The KIP will help fix a concurrency issue in Kafka which currently
> can
> > > > cause message loss or message duplication in consumer.
> > > >
> > > > Regards,
> > > > Dong
> > > >
> > >
> > >
> > >
> > > --
> > > -- Guozhang
> > >
> >
>
>
>
> --
> -- Guozhang
>

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Guozhang Wang]

"If consumer wants to consume message with offset 16, then consumer must have
already fetched message with offset 15"

--> this may not be always true right? What if consumer just call seek(16)
after construction and then poll without committed offset ever stored
before? Admittedly it is rare but we do not programmably disallow it.


Guozhang

On Tue, Jan 23, 2018 at 10:42 PM, Dong Lin  wrote:

> Hey Guozhang,
>
> Thanks much for reviewing the KIP!
>
> In the scenario you described, let's assume that broker A has messages with
> offset up to 10, and broker B has messages with offset up to 20. If
> consumer wants to consume message with offset 9, it will not receive
> OffsetOutOfRangeException
> from broker A.
>
> If consumer wants to consume message with offset 16, then consumer must
> have already fetched message with offset 15, which can only come from
> broker B. Because consumer will fetch from broker B only if leaderEpoch >=
> 2, then the current consumer leaderEpoch can not be 1 since this KIP
> prevents leaderEpoch rewind. Thus we will not have
> OffsetOutOfRangeException
> in this case.
>
> Does this address your question, or maybe there is more advanced scenario
> that the KIP does not handle?
>
> Thanks,
> Dong
>
> On Tue, Jan 23, 2018 at 9:43 PM, Guozhang Wang  wrote:
>
> > Thanks Dong, I made a pass over the wiki and it lgtm.
> >
> > Just a quick question: can we completely eliminate the
> > OffsetOutOfRangeException with this approach? Say if there is consecutive
> > leader changes such that the cached metadata's partition epoch is 1, and
> > the metadata fetch response returns  with partition epoch 2 pointing to
> > leader broker A, while the actual up-to-date metadata has partition
> epoch 3
> > whose leader is now broker B, the metadata refresh will still succeed and
> > the follow-up fetch request may still see OORE?
> >
> >
> > Guozhang
> >
> >
> > On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin  wrote:
> >
> > > Hi all,
> > >
> > > I would like to start the voting process for KIP-232:
> > >
> > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > > 232%3A+Detect+outdated+metadata+using+leaderEpoch+and+partitionEpoch
> > >
> > > The KIP will help fix a concurrency issue in Kafka which currently can
> > > cause message loss or message duplication in consumer.
> > >
> > > Regards,
> > > Dong
> > >
> >
> >
> >
> > --
> > -- Guozhang
> >
>



-- 
-- Guozhang

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Dong Lin]

Hey Guozhang,

Thanks much for reviewing the KIP!

In the scenario you described, let's assume that broker A has messages with
offset up to 10, and broker B has messages with offset up to 20. If
consumer wants to consume message with offset 9, it will not receive
OffsetOutOfRangeException
from broker A.

If consumer wants to consume message with offset 16, then consumer must
have already fetched message with offset 15, which can only come from
broker B. Because consumer will fetch from broker B only if leaderEpoch >=
2, then the current consumer leaderEpoch can not be 1 since this KIP
prevents leaderEpoch rewind. Thus we will not have OffsetOutOfRangeException
in this case.

Does this address your question, or maybe there is more advanced scenario
that the KIP does not handle?

Thanks,
Dong

On Tue, Jan 23, 2018 at 9:43 PM, Guozhang Wang  wrote:

> Thanks Dong, I made a pass over the wiki and it lgtm.
>
> Just a quick question: can we completely eliminate the
> OffsetOutOfRangeException with this approach? Say if there is consecutive
> leader changes such that the cached metadata's partition epoch is 1, and
> the metadata fetch response returns  with partition epoch 2 pointing to
> leader broker A, while the actual up-to-date metadata has partition epoch 3
> whose leader is now broker B, the metadata refresh will still succeed and
> the follow-up fetch request may still see OORE?
>
>
> Guozhang
>
>
> On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin  wrote:
>
> > Hi all,
> >
> > I would like to start the voting process for KIP-232:
> >
> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > 232%3A+Detect+outdated+metadata+using+leaderEpoch+and+partitionEpoch
> >
> > The KIP will help fix a concurrency issue in Kafka which currently can
> > cause message loss or message duplication in consumer.
> >
> > Regards,
> > Dong
> >
>
>
>
> --
> -- Guozhang
>

Re: [VOTE] KIP-232: Detect outdated metadata using leaderEpoch and partitionEpoch

[Guozhang Wang]

Thanks Dong, I made a pass over the wiki and it lgtm.

Just a quick question: can we completely eliminate the
OffsetOutOfRangeException with this approach? Say if there is consecutive
leader changes such that the cached metadata's partition epoch is 1, and
the metadata fetch response returns  with partition epoch 2 pointing to
leader broker A, while the actual up-to-date metadata has partition epoch 3
whose leader is now broker B, the metadata refresh will still succeed and
the follow-up fetch request may still see OORE?


Guozhang


On Tue, Jan 23, 2018 at 3:47 PM, Dong Lin  wrote:

> Hi all,
>
> I would like to start the voting process for KIP-232:
>
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> 232%3A+Detect+outdated+metadata+using+leaderEpoch+and+partitionEpoch
>
> The KIP will help fix a concurrency issue in Kafka which currently can
> cause message loss or message duplication in consumer.
>
> Regards,
> Dong
>



-- 
-- Guozhang