Hey all, I've updated the KIP to incorporate Jason's suggestions.
https://cwiki.apache.org/confluence/display/KAFKA/KIP-890%3A+Transactions+Server-Side+Defense
1. Use AddPartitionsToTxn + verify flag to check on old clients
2. Updated AddPartitionsToTxn API to support transaction batching
3. Mention IBP bump
4. Mention auth change on new AddPartitionsToTxn version.
I'm planning on opening a vote soon.
Thanks,
Justine
On Fri, Jan 6, 2023 at 3:32 PM Justine Olshan <jols...@confluent.io> wrote:
> Thanks Jason. Those changes make sense to me. I will update the KIP.
>
>
>
> On Fri, Jan 6, 2023 at 3:31 PM Jason Gustafson <ja...@confluent.io.invalid>
> wrote:
>
>> Hey Justine,
>>
>> > I was wondering about compatibility here. When we send requests
>> between brokers, we want to ensure that the receiving broker understands
>> the request (specifically the new fields). Typically this is done via
>> IBP/metadata version.
>> I'm trying to think if there is a way around it but I'm not sure there is.
>>
>> Yes. I think we would gate usage of this behind an IBP bump. Does that
>> seem
>> reasonable?
>>
>> > As for the improvements -- can you clarify how the multiple
>> transactional
>> IDs would help here? Were you thinking of a case where we wait/batch
>> multiple produce requests together? My understanding for now was 1
>> transactional ID and one validation per 1 produce request.
>>
>> Each call to `AddPartitionsToTxn` is essentially a write to the
>> transaction
>> log and must block on replication. The more we can fit into a single
>> request, the more writes we can do in parallel. The alternative is to make
>> use of more connections, but usually we prefer batching since the network
>> stack is not really optimized for high connection/request loads.
>>
>> > Finally with respect to the authorizations, I think it makes sense to
>> skip
>> topic authorizations, but I'm a bit confused by the "leader ID" field.
>> Wouldn't we just want to flag the request as from a broker (does it matter
>> which one?).
>>
>> We could also make it version-based. For the next version, we could
>> require
>> CLUSTER auth. So clients would not be able to use the API anymore, which
>> is
>> probably what we want.
>>
>> -Jason
>>
>> On Fri, Jan 6, 2023 at 10:43 AM Justine Olshan
>> <jols...@confluent.io.invalid>
>> wrote:
>>
>> > As a follow up, I was just thinking about the batching a bit more.
>> > I suppose if we have one request in flight and we queue up the other
>> > produce requests in some sort of purgatory, we could send information
>> out
>> > for all of them rather than one by one. So that would be a benefit of
>> > batching partitions to add per transaction.
>> >
>> > I'll need to think a bit more on the design of this part of the KIP, and
>> > will update the KIP in the next few days.
>> >
>> > Thanks,
>> > Justine
>> >
>> > On Fri, Jan 6, 2023 at 10:22 AM Justine Olshan <jols...@confluent.io>
>> > wrote:
>> >
>> > > Hey Jason -- thanks for the input -- I was just digging a bit deeper
>> into
>> > > the design + implementation of the validation calls here and what you
>> say
>> > > makes sense.
>> > >
>> > > I was wondering about compatibility here. When we send requests
>> > > between brokers, we want to ensure that the receiving broker
>> understands
>> > > the request (specifically the new fields). Typically this is done via
>> > > IBP/metadata version.
>> > > I'm trying to think if there is a way around it but I'm not sure there
>> > is.
>> > >
>> > > As for the improvements -- can you clarify how the multiple
>> transactional
>> > > IDs would help here? Were you thinking of a case where we wait/batch
>> > > multiple produce requests together? My understanding for now was 1
>> > > transactional ID and one validation per 1 produce request.
>> > >
>> > > Finally with respect to the authorizations, I think it makes sense to
>> > skip
>> > > topic authorizations, but I'm a bit confused by the "leader ID" field.
>> > > Wouldn't we just want to flag the request as from a broker (does it
>> > matter
>> > > which one?).
>> > >
>> > > I think I want to adopt these suggestions, just had a few questions on
>> > the
>> > > details.
>> > >
>> > > Thanks,
>> > > Justine
>> > >
>> > > On Thu, Jan 5, 2023 at 5:05 PM Jason Gustafson
>> > <ja...@confluent.io.invalid>
>> > > wrote:
>> > >
>> > >> Hi Justine,
>> > >>
>> > >> Thanks for the proposal.
>> > >>
>> > >> I was thinking about the implementation a little bit. In the current
>> > >> proposal, the behavior depends on whether we have an old or new
>> client.
>> > >> For
>> > >> old clients, we send `DescribeTransactions` and verify the result and
>> > for
>> > >> new clients, we send `AddPartitionsToTxn`. We might be able to
>> simplify
>> > >> the
>> > >> implementation if we can use the same request type. For example,
>> what if
>> > >> we
>> > >> bump the protocol version for `AddPartitionsToTxn` and add a
>> > >> `validateOnly`
>> > >> flag? For older versions, we can set `validateOnly=true` so that the
>> > >> request only returns successfully if the partition had already been
>> > added.
>> > >> For new versions, we can set `validateOnly=false` and the partition
>> will
>> > >> be
>> > >> added to the transaction. The other slightly annoying thing that this
>> > >> would
>> > >> get around is the need to collect the transaction state for all
>> > partitions
>> > >> even when we only care about a subset.
>> > >>
>> > >> Some additional improvements to consider:
>> > >>
>> > >> - We can give `AddPartitionsToTxn` better batch support for
>> inter-broker
>> > >> usage. Currently we only allow one `TransactionalId` to be specified,
>> > but
>> > >> the broker may get some benefit being able to batch across multiple
>> > >> transactions.
>> > >> - Another small improvement is skipping topic authorization checks
>> for
>> > >> `AddPartitionsToTxn` when the request is from a broker. Perhaps we
>> can
>> > add
>> > >> a field for the `LeaderId` or something like that and require CLUSTER
>> > >> permission when set.
>> > >>
>> > >> Best,
>> > >> Jason
>> > >>
>> > >>
>> > >>
>> > >> On Mon, Dec 19, 2022 at 3:56 PM Jun Rao <j...@confluent.io.invalid>
>> > wrote:
>> > >>
>> > >> > Hi, Justine,
>> > >> >
>> > >> > Thanks for the explanation. It makes sense to me now.
>> > >> >
>> > >> > Jun
>> > >> >
>> > >> > On Mon, Dec 19, 2022 at 1:42 PM Justine Olshan
>> > >> > <jols...@confluent.io.invalid>
>> > >> > wrote:
>> > >> >
>> > >> > > Hi Jun,
>> > >> > >
>> > >> > > My understanding of the mechanism is that when we get to the last
>> > >> epoch,
>> > >> > we
>> > >> > > increment to the fencing/last epoch and if any further requests
>> come
>> > >> in
>> > >> > for
>> > >> > > this producer ID they are fenced. Then the producer gets a new ID
>> > and
>> > >> > > restarts with epoch/sequence 0. The fenced epoch sticks around
>> for
>> > the
>> > >> > > duration of producer.id.expiration.ms and blocks any late
>> messages
>> > >> > there.
>> > >> > > The new ID will get to take advantage of the improved semantics
>> > around
>> > >> > > non-zero start sequences. So I think we are covered.
>> > >> > >
>> > >> > > The only potential issue is overloading the cache, but hopefully
>> the
>> > >> > > improvements (lowered producer.id.expiration.ms) will help with
>> > that.
>> > >> > Let
>> > >> > > me know if you still have concerns.
>> > >> > >
>> > >> > > Thanks,
>> > >> > > Justine
>> > >> > >
>> > >> > > On Mon, Dec 19, 2022 at 10:24 AM Jun Rao
>> <j...@confluent.io.invalid>
>> > >> > wrote:
>> > >> > >
>> > >> > > > Hi, Justine,
>> > >> > > >
>> > >> > > > Thanks for the explanation.
>> > >> > > >
>> > >> > > > 70. The proposed fencing logic doesn't apply when pid changes,
>> is
>> > >> that
>> > >> > > > right? If so, I am not sure how complete we are addressing this
>> > >> issue
>> > >> > if
>> > >> > > > the pid changes more frequently.
>> > >> > > >
>> > >> > > > Thanks,
>> > >> > > >
>> > >> > > > Jun
>> > >> > > >
>> > >> > > >
>> > >> > > >
>> > >> > > > On Fri, Dec 16, 2022 at 9:16 AM Justine Olshan
>> > >> > > > <jols...@confluent.io.invalid>
>> > >> > > > wrote:
>> > >> > > >
>> > >> > > > > Hi Jun,
>> > >> > > > >
>> > >> > > > > Thanks for replying!
>> > >> > > > >
>> > >> > > > > 70.We already do the overflow mechanism, so my change would
>> just
>> > >> make
>> > >> > > it
>> > >> > > > > happen more often.
>> > >> > > > > I was also not suggesting a new field in the log, but in the
>> > >> > response,
>> > >> > > > > which would be gated by the client version. Sorry if
>> something
>> > >> there
>> > >> > is
>> > >> > > > > unclear. I think we are starting to diverge.
>> > >> > > > > The goal of this KIP is to not change to the marker format at
>> > all.
>> > >> > > > >
>> > >> > > > > 71. Yes, I guess I was going under the assumption that the
>> log
>> > >> would
>> > >> > > just
>> > >> > > > > look at its last epoch and treat it as the current epoch. I
>> > >> suppose
>> > >> > we
>> > >> > > > can
>> > >> > > > > have some special logic that if the last epoch was on a
>> marker
>> > we
>> > >> > > > actually
>> > >> > > > > expect the next epoch or something like that. We just need to
>> > >> > > distinguish
>> > >> > > > > based on whether we had a commit/abort marker.
>> > >> > > > >
>> > >> > > > > 72.
>> > >> > > > > > if the producer epoch hasn't been bumped on the
>> > >> > > > > broker, it seems that the stucked message will fail the
>> sequence
>> > >> > > > validation
>> > >> > > > > and will be ignored. If the producer epoch has been bumped,
>> we
>> > >> ignore
>> > >> > > the
>> > >> > > > > sequence check and the stuck message could be appended to the
>> > log.
>> > >> > So,
>> > >> > > is
>> > >> > > > > the latter case that we want to guard?
>> > >> > > > >
>> > >> > > > > I'm not sure I follow that "the message will fail the
>> sequence
>> > >> > > > validation".
>> > >> > > > > In some of these cases, we had an abort marker (due to an
>> error)
>> > >> and
>> > >> > > then
>> > >> > > > > the late message comes in with the correct sequence number.
>> This
>> > >> is a
>> > >> > > > case
>> > >> > > > > covered by the KIP.
>> > >> > > > > The latter case is actually not something we've considered
>> > here. I
>> > >> > > think
>> > >> > > > > generally when we bump the epoch, we are accepting that the
>> > >> sequence
>> > >> > > does
>> > >> > > > > not need to be checked anymore. My understanding is also
>> that we
>> > >> > don't
>> > >> > > > > typically bump epoch mid transaction (based on a quick look
>> at
>> > the
>> > >> > > code)
>> > >> > > > > but let me know if that is the case.
>> > >> > > > >
>> > >> > > > > Thanks,
>> > >> > > > > Justine
>> > >> > > > >
>> > >> > > > > On Thu, Dec 15, 2022 at 12:23 PM Jun Rao
>> > <j...@confluent.io.invalid
>> > >> >
>> > >> > > > wrote:
>> > >> > > > >
>> > >> > > > > > Hi, Justine,
>> > >> > > > > >
>> > >> > > > > > Thanks for the reply.
>> > >> > > > > >
>> > >> > > > > > 70. Assigning a new pid on int overflow seems a bit hacky.
>> If
>> > we
>> > >> > > need a
>> > >> > > > > txn
>> > >> > > > > > level id, it will be better to model this explicitly.
>> Adding a
>> > >> new
>> > >> > > > field
>> > >> > > > > > would require a bit more work since it requires a new txn
>> > marker
>> > >> > > format
>> > >> > > > > in
>> > >> > > > > > the log. So, we probably need to guard it with an IBP or
>> > >> metadata
>> > >> > > > version
>> > >> > > > > > and document the impact on downgrade once the new format is
>> > >> written
>> > >> > > to
>> > >> > > > > the
>> > >> > > > > > log.
>> > >> > > > > >
>> > >> > > > > > 71. Hmm, once the marker is written, the partition will
>> expect
>> > >> the
>> > >> > > next
>> > >> > > > > > append to be on the next epoch. Does that cover the case
>> you
>> > >> > > mentioned?
>> > >> > > > > >
>> > >> > > > > > 72. Also, just to be clear on the stucked message issue
>> > >> described
>> > >> > in
>> > >> > > > the
>> > >> > > > > > motivation. With EoS, we also validate the sequence id for
>> > >> > > idempotency.
>> > >> > > > > So,
>> > >> > > > > > with the current logic, if the producer epoch hasn't been
>> > >> bumped on
>> > >> > > the
>> > >> > > > > > broker, it seems that the stucked message will fail the
>> > sequence
>> > >> > > > > validation
>> > >> > > > > > and will be ignored. If the producer epoch has been
>> bumped, we
>> > >> > ignore
>> > >> > > > the
>> > >> > > > > > sequence check and the stuck message could be appended to
>> the
>> > >> log.
>> > >> > > So,
>> > >> > > > is
>> > >> > > > > > the latter case that we want to guard?
>> > >> > > > > >
>> > >> > > > > > Thanks,
>> > >> > > > > >
>> > >> > > > > > Jun
>> > >> > > > > >
>> > >> > > > > > On Wed, Dec 14, 2022 at 10:44 AM Justine Olshan
>> > >> > > > > > <jols...@confluent.io.invalid> wrote:
>> > >> > > > > >
>> > >> > > > > > > Matthias — thanks again for taking time to look a this.
>> You
>> > >> said:
>> > >> > > > > > >
>> > >> > > > > > > > My proposal was only focusing to avoid dangling
>> > >> > > > > > >
>> > >> > > > > > > transactions if records are added without registered
>> > >> partition.
>> > >> > --
>> > >> > > > > Maybe
>> > >> > > > > > >
>> > >> > > > > > > you can add a few more details to the KIP about this
>> > scenario
>> > >> for
>> > >> > > > > better
>> > >> > > > > > >
>> > >> > > > > > > documentation purpose?
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > > I'm not sure I understand what you mean here. The
>> motivation
>> > >> > > section
>> > >> > > > > > > describes two scenarios about how the record can be added
>> > >> > without a
>> > >> > > > > > > registered partition:
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > > > This can happen when a message gets stuck or delayed
>> due
>> > to
>> > >> > > > > networking
>> > >> > > > > > > issues or a network partition, the transaction aborts,
>> and
>> > >> then
>> > >> > the
>> > >> > > > > > delayed
>> > >> > > > > > > message finally comes in.
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > > > Another way hanging transactions can occur is that a
>> > client
>> > >> is
>> > >> > > > buggy
>> > >> > > > > > and
>> > >> > > > > > > may somehow try to write to a partition before it adds
>> the
>> > >> > > partition
>> > >> > > > to
>> > >> > > > > > the
>> > >> > > > > > > transaction.
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > > For the first example of this would it be helpful to say
>> > that
>> > >> > this
>> > >> > > > > > message
>> > >> > > > > > > comes in after the abort, but before the partition is
>> added
>> > to
>> > >> > the
>> > >> > > > next
>> > >> > > > > > > transaction so it becomes "hanging." Perhaps the next
>> > sentence
>> > >> > > > > describing
>> > >> > > > > > > the message becoming part of the next transaction (a
>> > different
>> > >> > > case)
>> > >> > > > > was
>> > >> > > > > > > not properly differentiated.
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > > > > Jun — thanks for reading the KIP.
>> > >> > > > > > >
>> > >> > > > > > > 70. The int typing was a concern. Currently we have a
>> > >> mechanism
>> > >> > in
>> > >> > > > > place
>> > >> > > > > > to
>> > >> > > > > > > fence the final epoch when the epoch is about to overflow
>> > and
>> > >> > > assign
>> > >> > > > a
>> > >> > > > > > new
>> > >> > > > > > > producer ID with epoch 0. Of course, this is a bit tricky
>> > >> when it
>> > >> > > > comes
>> > >> > > > > > to
>> > >> > > > > > > the response back to the client.
>> > >> > > > > > > Making this a long could be another option, but I wonder
>> are
>> > >> > there
>> > >> > > > any
>> > >> > > > > > > implications on changing this field if the epoch is
>> > persisted
>> > >> to
>> > >> > > > disk?
>> > >> > > > > > I'd
>> > >> > > > > > > need to check the usages.
>> > >> > > > > > >
>> > >> > > > > > > 71.This was something Matthias asked about as well. I was
>> > >> > > > considering a
>> > >> > > > > > > possible edge case where a produce request from a new
>> > >> transaction
>> > >> > > > > somehow
>> > >> > > > > > > gets sent right after the marker is written, but before
>> the
>> > >> > > producer
>> > >> > > > is
>> > >> > > > > > > alerted of the newly bumped epoch. In this case, we may
>> > >> include
>> > >> > > this
>> > >> > > > > > record
>> > >> > > > > > > when we don't want to. I suppose we could try to do
>> > something
>> > >> > > client
>> > >> > > > > side
>> > >> > > > > > > to bump the epoch after sending an endTxn as well in this
>> > >> > scenario
>> > >> > > —
>> > >> > > > > but
>> > >> > > > > > I
>> > >> > > > > > > wonder how it would work when the server is aborting
>> based
>> > on
>> > >> a
>> > >> > > > > > server-side
>> > >> > > > > > > error. I could also be missing something and this
>> scenario
>> > is
>> > >> > > > actually
>> > >> > > > > > not
>> > >> > > > > > > possible.
>> > >> > > > > > >
>> > >> > > > > > > Thanks again to everyone reading and commenting. Let me
>> know
>> > >> > about
>> > >> > > > any
>> > >> > > > > > > further questions or comments.
>> > >> > > > > > >
>> > >> > > > > > > Justine
>> > >> > > > > > >
>> > >> > > > > > > On Wed, Dec 14, 2022 at 9:41 AM Jun Rao
>> > >> <j...@confluent.io.invalid
>> > >> > >
>> > >> > > > > > wrote:
>> > >> > > > > > >
>> > >> > > > > > > > Hi, Justine,
>> > >> > > > > > > >
>> > >> > > > > > > > Thanks for the KIP. A couple of comments.
>> > >> > > > > > > >
>> > >> > > > > > > > 70. Currently, the producer epoch is an int. I am not
>> sure
>> > >> if
>> > >> > > it's
>> > >> > > > > > enough
>> > >> > > > > > > > to accommodate all transactions in the lifetime of a
>> > >> producer.
>> > >> > > > Should
>> > >> > > > > > we
>> > >> > > > > > > > change that to a long or add a new long field like
>> txnId?
>> > >> > > > > > > >
>> > >> > > > > > > > 71. "it will write the prepare commit message with a
>> > bumped
>> > >> > epoch
>> > >> > > > and
>> > >> > > > > > > send
>> > >> > > > > > > > WriteTxnMarkerRequests with the bumped epoch." Hmm, the
>> > >> epoch
>> > >> > is
>> > >> > > > > > > associated
>> > >> > > > > > > > with the current txn right? So, it seems weird to
>> write a
>> > >> > commit
>> > >> > > > > > message
>> > >> > > > > > > > with a bumped epoch. Should we only bump up the epoch
>> in
>> > >> > > > > EndTxnResponse
>> > >> > > > > > > and
>> > >> > > > > > > > rename the field to sth like nextProducerEpoch?
>> > >> > > > > > > >
>> > >> > > > > > > > Thanks,
>> > >> > > > > > > >
>> > >> > > > > > > > Jun
>> > >> > > > > > > >
>> > >> > > > > > > >
>> > >> > > > > > > >
>> > >> > > > > > > > On Mon, Dec 12, 2022 at 8:54 PM Matthias J. Sax <
>> > >> > > mj...@apache.org>
>> > >> > > > > > > wrote:
>> > >> > > > > > > >
>> > >> > > > > > > > > Thanks for the background.
>> > >> > > > > > > > >
>> > >> > > > > > > > > 20/30: SGTM. My proposal was only focusing to avoid
>> > >> dangling
>> > >> > > > > > > > > transactions if records are added without registered
>> > >> > partition.
>> > >> > > > --
>> > >> > > > > > > Maybe
>> > >> > > > > > > > > you can add a few more details to the KIP about this
>> > >> scenario
>> > >> > > for
>> > >> > > > > > > better
>> > >> > > > > > > > > documentation purpose?
>> > >> > > > > > > > >
>> > >> > > > > > > > > 40: I think you hit a fair point about race
>> conditions
>> > or
>> > >> > > client
>> > >> > > > > bugs
>> > >> > > > > > > > > (incorrectly not bumping the epoch). The
>> > >> complexity/confusion
>> > >> > > for
>> > >> > > > > > using
>> > >> > > > > > > > > the bumped epoch I see, is mainly for internal
>> > debugging,
>> > >> ie,
>> > >> > > > > > > inspecting
>> > >> > > > > > > > > log segment dumps -- it seems harder to reason about
>> the
>> > >> > system
>> > >> > > > for
>> > >> > > > > > us
>> > >> > > > > > > > > humans. But if we get better guarantees, it would be
>> > >> worth to
>> > >> > > use
>> > >> > > > > the
>> > >> > > > > > > > > bumped epoch.
>> > >> > > > > > > > >
>> > >> > > > > > > > > 60: as I mentioned already, I don't know the broker
>> > >> internals
>> > >> > > to
>> > >> > > > > > > provide
>> > >> > > > > > > > > more input. So if nobody else chimes in, we should
>> just
>> > >> move
>> > >> > > > > forward
>> > >> > > > > > > > > with your proposal.
>> > >> > > > > > > > >
>> > >> > > > > > > > >
>> > >> > > > > > > > > -Matthias
>> > >> > > > > > > > >
>> > >> > > > > > > > >
>> > >> > > > > > > > > On 12/6/22 4:22 PM, Justine Olshan wrote:
>> > >> > > > > > > > > > Hi all,
>> > >> > > > > > > > > > After Artem's questions about error behavior, I've
>> > >> > > re-evaluated
>> > >> > > > > the
>> > >> > > > > > > > > > unknown producer ID exception and had some
>> discussions
>> > >> > > offline.
>> > >> > > > > > > > > >
>> > >> > > > > > > > > > I think generally it makes sense to simplify error
>> > >> handling
>> > >> > > in
>> > >> > > > > > cases
>> > >> > > > > > > > like
>> > >> > > > > > > > > > this and the UNKNOWN_PRODUCER_ID error has a pretty
>> > long
>> > >> > and
>> > >> > > > > > > > complicated
>> > >> > > > > > > > > > history. Because of this, I propose adding a new
>> error
>> > >> code
>> > >> > > > > > > > > ABORTABLE_ERROR
>> > >> > > > > > > > > > that when encountered by new clients (gated by the
>> > >> produce
>> > >> > > > > request
>> > >> > > > > > > > > version)
>> > >> > > > > > > > > > will simply abort the transaction. This allows the
>> > >> server
>> > >> > to
>> > >> > > > have
>> > >> > > > > > > some
>> > >> > > > > > > > > say
>> > >> > > > > > > > > > in whether the client aborts and makes handling
>> much
>> > >> > simpler.
>> > >> > > > In
>> > >> > > > > > the
>> > >> > > > > > > > > > future, we can also use this error in other
>> situations
>> > >> > where
>> > >> > > we
>> > >> > > > > > want
>> > >> > > > > > > to
>> > >> > > > > > > > > > abort the transactions. We can even use on other
>> apis.
>> > >> > > > > > > > > >
>> > >> > > > > > > > > > I've added this to the KIP. Let me know if there
>> are
>> > any
>> > >> > > > > questions
>> > >> > > > > > or
>> > >> > > > > > > > > > issues.
>> > >> > > > > > > > > >
>> > >> > > > > > > > > > Justine
>> > >> > > > > > > > > >
>> > >> > > > > > > > > > On Fri, Dec 2, 2022 at 10:22 AM Justine Olshan <
>> > >> > > > > > jols...@confluent.io
>> > >> > > > > > > >
>> > >> > > > > > > > > wrote:
>> > >> > > > > > > > > >
>> > >> > > > > > > > > >> Hey Matthias,
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> 20/30 — Maybe I also didn't express myself
>> clearly.
>> > For
>> > >> > > older
>> > >> > > > > > > clients
>> > >> > > > > > > > we
>> > >> > > > > > > > > >> don't have a way to distinguish between a previous
>> > and
>> > >> the
>> > >> > > > > current
>> > >> > > > > > > > > >> transaction since we don't have the epoch bump.
>> This
>> > >> means
>> > >> > > > that
>> > >> > > > > a
>> > >> > > > > > > late
>> > >> > > > > > > > > >> message from the previous transaction may be
>> added to
>> > >> the
>> > >> > > new
>> > >> > > > > one.
>> > >> > > > > > > > With
>> > >> > > > > > > > > >> older clients — we can't guarantee this won't
>> happen
>> > >> if we
>> > >> > > > > already
>> > >> > > > > > > > sent
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >> addPartitionsToTxn call (why we make changes for
>> the
>> > >> newer
>> > >> > > > > client)
>> > >> > > > > > > but
>> > >> > > > > > > > > we
>> > >> > > > > > > > > >> can at least gate some by ensuring that the
>> partition
>> > >> has
>> > >> > > been
>> > >> > > > > > added
>> > >> > > > > > > > to
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >> transaction. The rationale here is that there are
>> > >> likely
>> > >> > > LESS
>> > >> > > > > late
>> > >> > > > > > > > > arrivals
>> > >> > > > > > > > > >> as time goes on, so hopefully most late arrivals
>> will
>> > >> come
>> > >> > > in
>> > >> > > > > > BEFORE
>> > >> > > > > > > > the
>> > >> > > > > > > > > >> addPartitionsToTxn call. Those that arrive before
>> > will
>> > >> be
>> > >> > > > > properly
>> > >> > > > > > > > gated
>> > >> > > > > > > > > >> with the describeTransactions approach.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> If we take the approach you suggested, ANY late
>> > arrival
>> > >> > > from a
>> > >> > > > > > > > previous
>> > >> > > > > > > > > >> transaction will be added. And we don't want
>> that. I
>> > >> also
>> > >> > > > don't
>> > >> > > > > > see
>> > >> > > > > > > > any
>> > >> > > > > > > > > >> benefit in sending addPartitionsToTxn over the
>> > >> > describeTxns
>> > >> > > > > call.
>> > >> > > > > > > They
>> > >> > > > > > > > > will
>> > >> > > > > > > > > >> both be one extra RPC to the Txn coordinator.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> To be clear — newer clients will use
>> > addPartitionsToTxn
>> > >> > > > instead
>> > >> > > > > of
>> > >> > > > > > > the
>> > >> > > > > > > > > >> DescribeTxns.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> 40)
>> > >> > > > > > > > > >> My concern is that if we have some delay in the
>> > client
>> > >> to
>> > >> > > bump
>> > >> > > > > the
>> > >> > > > > > > > > epoch,
>> > >> > > > > > > > > >> it could continue to send epoch 73 and those
>> records
>> > >> would
>> > >> > > not
>> > >> > > > > be
>> > >> > > > > > > > > fenced.
>> > >> > > > > > > > > >> Perhaps this is not an issue if we don't allow the
>> > next
>> > >> > > > produce
>> > >> > > > > to
>> > >> > > > > > > go
>> > >> > > > > > > > > >> through before the EndTxn request returns. I'm
>> also
>> > >> > thinking
>> > >> > > > > about
>> > >> > > > > > > > > cases of
>> > >> > > > > > > > > >> failure. I will need to think on this a bit.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> I wasn't sure if it was that confusing. But if we
>> > >> think it
>> > >> > > is,
>> > >> > > > > we
>> > >> > > > > > > can
>> > >> > > > > > > > > >> investigate other ways.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> 60)
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> I'm not sure these are the same purgatories since
>> one
>> > >> is a
>> > >> > > > > produce
>> > >> > > > > > > > > >> purgatory (I was planning on using a callback
>> rather
>> > >> than
>> > >> > > > > > purgatory)
>> > >> > > > > > > > and
>> > >> > > > > > > > > >> the other is simply a request to append to the
>> log.
>> > Not
>> > >> > sure
>> > >> > > > we
>> > >> > > > > > have
>> > >> > > > > > > > any
>> > >> > > > > > > > > >> structure here for ordering, but my understanding
>> is
>> > >> that
>> > >> > > the
>> > >> > > > > > broker
>> > >> > > > > > > > > could
>> > >> > > > > > > > > >> handle the write request before it hears back from
>> > the
>> > >> Txn
>> > >> > > > > > > > Coordinator.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> Let me know if I misunderstood something or
>> something
>> > >> was
>> > >> > > > > unclear.
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> Justine
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >> On Thu, Dec 1, 2022 at 12:15 PM Matthias J. Sax <
>> > >> > > > > mj...@apache.org
>> > >> > > > > > >
>> > >> > > > > > > > > wrote:
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >>> Thanks for the details Justine!
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>> 20)
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> The client side change for 2 is removing the
>> > >> > addPartitions
>> > >> > > > to
>> > >> > > > > > > > > >>> transaction
>> > >> > > > > > > > > >>>> call. We don't need to make this from the
>> producer
>> > to
>> > >> > the
>> > >> > > > txn
>> > >> > > > > > > > > >>> coordinator,
>> > >> > > > > > > > > >>>> only server side.
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> I think I did not express myself clearly. I
>> > understand
>> > >> > that
>> > >> > > > we
>> > >> > > > > > can
>> > >> > > > > > > > (and
>> > >> > > > > > > > > >>> should) change the producer to not send the
>> > >> > `addPartitions`
>> > >> > > > > > request
>> > >> > > > > > > > any
>> > >> > > > > > > > > >>> longer. But I don't thinks it's requirement to
>> > change
>> > >> the
>> > >> > > > > broker?
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> What I am trying to say is: as a safe-guard and
>> > >> > improvement
>> > >> > > > for
>> > >> > > > > > > older
>> > >> > > > > > > > > >>> producers, the partition leader can just send the
>> > >> > > > > `addPartitions`
>> > >> > > > > > > > > >>> request to the TX-coordinator in any case -- if
>> the
>> > >> old
>> > >> > > > > producer
>> > >> > > > > > > > > >>> correctly did send the `addPartition` request to
>> the
>> > >> > > > > > TX-coordinator
>> > >> > > > > > > > > >>> already, the TX-coordinator can just "ignore" is
>> as
>> > >> > > > idempotent.
>> > >> > > > > > > > > However,
>> > >> > > > > > > > > >>> if the old producer has a bug and did forget to
>> sent
>> > >> the
>> > >> > > > > > > > `addPartition`
>> > >> > > > > > > > > >>> request, we would now ensure that the partition
>> is
>> > >> indeed
>> > >> > > > added
>> > >> > > > > > to
>> > >> > > > > > > > the
>> > >> > > > > > > > > >>> TX and thus fix a potential producer bug (even
>> if we
>> > >> > don't
>> > >> > > > get
>> > >> > > > > > the
>> > >> > > > > > > > > >>> fencing via the bump epoch). -- It seems to be a
>> > good
>> > >> > > > > > improvement?
>> > >> > > > > > > Or
>> > >> > > > > > > > > is
>> > >> > > > > > > > > >>> there a reason to not do this?
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>> 30)
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> Transaction is ongoing = partition was added to
>> > >> > > transaction
>> > >> > > > > via
>> > >> > > > > > > > > >>>> addPartitionsToTxn. We check this with the
>> > >> > > > > DescribeTransactions
>> > >> > > > > > > > call.
>> > >> > > > > > > > > >>> Let
>> > >> > > > > > > > > >>>> me know if this wasn't sufficiently explained
>> here:
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> If we do what I propose in (20), we don't really
>> > need
>> > >> to
>> > >> > > make
>> > >> > > > > > this
>> > >> > > > > > > > > >>> `DescribeTransaction` call, as the partition
>> leader
>> > >> adds
>> > >> > > the
>> > >> > > > > > > > partition
>> > >> > > > > > > > > >>> for older clients and we get this check for free.
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>> 40)
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> The idea here is that if any messages somehow
>> come
>> > in
>> > >> > > before
>> > >> > > > > we
>> > >> > > > > > > get
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >>> new
>> > >> > > > > > > > > >>>> epoch to the producer, they will be fenced.
>> > However,
>> > >> if
>> > >> > we
>> > >> > > > > don't
>> > >> > > > > > > > think
>> > >> > > > > > > > > >>> this
>> > >> > > > > > > > > >>>> is necessary, it can be discussed
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> I agree that we should have epoch fencing. My
>> > >> question is
>> > >> > > > > > > different:
>> > >> > > > > > > > > >>> Assume we are at epoch 73, and we have an ongoing
>> > >> > > > transaction,
>> > >> > > > > > that
>> > >> > > > > > > > is
>> > >> > > > > > > > > >>> committed. It seems natural to write the "prepare
>> > >> commit"
>> > >> > > > > marker
>> > >> > > > > > > and
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >>> `WriteTxMarkerRequest` both with epoch 73, too,
>> as
>> > it
>> > >> > > belongs
>> > >> > > > > to
>> > >> > > > > > > the
>> > >> > > > > > > > > >>> current transaction. Of course, we now also bump
>> the
>> > >> > epoch
>> > >> > > > and
>> > >> > > > > > > expect
>> > >> > > > > > > > > >>> the next requests to have epoch 74, and would
>> reject
>> > >> an
>> > >> > > > request
>> > >> > > > > > > with
>> > >> > > > > > > > > >>> epoch 73, as the corresponding TX for epoch 73
>> was
>> > >> > already
>> > >> > > > > > > committed.
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> It seems you propose to write the "prepare commit
>> > >> marker"
>> > >> > > and
>> > >> > > > > > > > > >>> `WriteTxMarkerRequest` with epoch 74 though, what
>> > >> would
>> > >> > > work,
>> > >> > > > > but
>> > >> > > > > > > it
>> > >> > > > > > > > > >>> seems confusing. Is there a reason why we would
>> use
>> > >> the
>> > >> > > > bumped
>> > >> > > > > > > epoch
>> > >> > > > > > > > 74
>> > >> > > > > > > > > >>> instead of the current epoch 73?
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>> 60)
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> When we are checking if the transaction is
>> ongoing,
>> > >> we
>> > >> > > need
>> > >> > > > to
>> > >> > > > > > > make
>> > >> > > > > > > > a
>> > >> > > > > > > > > >>> round
>> > >> > > > > > > > > >>>> trip from the leader partition to the
>> transaction
>> > >> > > > coordinator.
>> > >> > > > > > In
>> > >> > > > > > > > the
>> > >> > > > > > > > > >>> time
>> > >> > > > > > > > > >>>> we are waiting for this message to come back, in
>> > >> theory
>> > >> > we
>> > >> > > > > could
>> > >> > > > > > > > have
>> > >> > > > > > > > > >>> sent
>> > >> > > > > > > > > >>>> a commit/abort call that would make the original
>> > >> result
>> > >> > of
>> > >> > > > the
>> > >> > > > > > > check
>> > >> > > > > > > > > >>> out of
>> > >> > > > > > > > > >>>> date. That is why we can check the leader state
>> > >> before
>> > >> > we
>> > >> > > > > write
>> > >> > > > > > to
>> > >> > > > > > > > the
>> > >> > > > > > > > > >>> log.
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> Thanks. Got it.
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> However, is this really an issue? We put the
>> produce
>> > >> > > request
>> > >> > > > in
>> > >> > > > > > > > > >>> purgatory, so how could we process the
>> > >> > > > `WriteTxnMarkerRequest`
>> > >> > > > > > > first?
>> > >> > > > > > > > > >>> Don't we need to put the `WriteTxnMarkerRequest`
>> > into
>> > >> > > > > purgatory,
>> > >> > > > > > > too,
>> > >> > > > > > > > > >>> for this case, and process both request in-order?
>> > >> (Again,
>> > >> > > my
>> > >> > > > > > broker
>> > >> > > > > > > > > >>> knowledge is limited and maybe we don't maintain
>> > >> request
>> > >> > > > order
>> > >> > > > > > for
>> > >> > > > > > > > this
>> > >> > > > > > > > > >>> case, what seems to be an issue IMHO, and I am
>> > >> wondering
>> > >> > if
>> > >> > > > > > > changing
>> > >> > > > > > > > > >>> request handling to preserve order for this case
>> > >> might be
>> > >> > > the
>> > >> > > > > > > cleaner
>> > >> > > > > > > > > >>> solution?)
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> -Matthias
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>> On 11/30/22 3:28 PM, Artem Livshits wrote:
>> > >> > > > > > > > > >>>> Hi Justine,
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> I think the interesting part is not in this
>> logic
>> > >> > (because
>> > >> > > > it
>> > >> > > > > > > tries
>> > >> > > > > > > > to
>> > >> > > > > > > > > >>>> figure out when UNKNOWN_PRODUCER_ID is retriable
>> > and
>> > >> if
>> > >> > > it's
>> > >> > > > > > > > > retryable,
>> > >> > > > > > > > > >>>> it's definitely not fatal), but what happens
>> when
>> > >> this
>> > >> > > logic
>> > >> > > > > > > doesn't
>> > >> > > > > > > > > >>> return
>> > >> > > > > > > > > >>>> 'true' and falls through. In the old clients it
>> > >> seems
>> > >> > to
>> > >> > > be
>> > >> > > > > > > fatal,
>> > >> > > > > > > > if
>> > >> > > > > > > > > >>> we
>> > >> > > > > > > > > >>>> keep the behavior in the new clients, I'd
>> expect it
>> > >> > would
>> > >> > > be
>> > >> > > > > > fatal
>> > >> > > > > > > > as
>> > >> > > > > > > > > >>> well.
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> -Artem
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>> On Tue, Nov 29, 2022 at 11:57 AM Justine Olshan
>> > >> > > > > > > > > >>>> <jols...@confluent.io.invalid> wrote:
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>>> Hi Artem and Jeff,
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> Thanks for taking a look and sorry for the slow
>> > >> > response.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> You both mentioned the change to handle
>> > >> > > UNKNOWN_PRODUCER_ID
>> > >> > > > > > > errors.
>> > >> > > > > > > > > To
>> > >> > > > > > > > > >>> be
>> > >> > > > > > > > > >>>>> clear — this error code will only be sent again
>> > when
>> > >> > the
>> > >> > > > > > client's
>> > >> > > > > > > > > >>> request
>> > >> > > > > > > > > >>>>> version is high enough to ensure we handle it
>> > >> > correctly.
>> > >> > > > > > > > > >>>>> The current (Java) client handles this by the
>> > >> following
>> > >> > > > > > (somewhat
>> > >> > > > > > > > > long)
>> > >> > > > > > > > > >>>>> code snippet:
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // An UNKNOWN_PRODUCER_ID means that we have
>> lost
>> > >> the
>> > >> > > > > producer
>> > >> > > > > > > > state
>> > >> > > > > > > > > >>> on the
>> > >> > > > > > > > > >>>>> broker. Depending on the log start
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // offset, we may want to retry these, as
>> > described
>> > >> for
>> > >> > > > each
>> > >> > > > > > case
>> > >> > > > > > > > > >>> below. If
>> > >> > > > > > > > > >>>>> none of those apply, then for the
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // idempotent producer, we will locally bump
>> the
>> > >> epoch
>> > >> > > and
>> > >> > > > > > reset
>> > >> > > > > > > > the
>> > >> > > > > > > > > >>>>> sequence numbers of in-flight batches from
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // sequence 0, then retry the failed batch,
>> which
>> > >> > should
>> > >> > > > now
>> > >> > > > > > > > succeed.
>> > >> > > > > > > > > >>> For
>> > >> > > > > > > > > >>>>> the transactional producer, allow the
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // batch to fail. When processing the failed
>> > batch,
>> > >> we
>> > >> > > will
>> > >> > > > > > > > > transition
>> > >> > > > > > > > > >>> to
>> > >> > > > > > > > > >>>>> an abortable error and set a flag
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // indicating that we need to bump the epoch
>> (if
>> > >> > > supported
>> > >> > > > by
>> > >> > > > > > the
>> > >> > > > > > > > > >>> broker).
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> if (error == Errors.*UNKNOWN_PRODUCER_ID*) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> if (response.logStartOffset == -1) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // We don't know the log start offset
>> > with
>> > >> > this
>> > >> > > > > > > response.
>> > >> > > > > > > > > We
>> > >> > > > > > > > > >>> should
>> > >> > > > > > > > > >>>>> just retry the request until we get it.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // The UNKNOWN_PRODUCER_ID error code
>> > was
>> > >> > added
>> > >> > > > > along
>> > >> > > > > > > > with
>> > >> > > > > > > > > >>> the new
>> > >> > > > > > > > > >>>>> ProduceResponse which includes the
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // logStartOffset. So the '-1'
>> sentinel
>> > is
>> > >> > not
>> > >> > > > for
>> > >> > > > > > > > backward
>> > >> > > > > > > > > >>>>> compatibility. Instead, it is possible for
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // a broker to not know the
>> > >> logStartOffset at
>> > >> > > > when
>> > >> > > > > it
>> > >> > > > > > > is
>> > >> > > > > > > > > >>> returning
>> > >> > > > > > > > > >>>>> the response because the partition
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // may have moved away from the
>> broker
>> > >> from
>> > >> > the
>> > >> > > > > time
>> > >> > > > > > > the
>> > >> > > > > > > > > >>> error was
>> > >> > > > > > > > > >>>>> initially raised to the time the
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // response was being constructed. In
>> > >> these
>> > >> > > > cases,
>> > >> > > > > we
>> > >> > > > > > > > > should
>> > >> > > > > > > > > >>> just
>> > >> > > > > > > > > >>>>> retry the request: we are guaranteed
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // to eventually get a logStartOffset
>> > once
>> > >> > > things
>> > >> > > > > > > settle
>> > >> > > > > > > > > down.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> return true;
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> }
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> if (batch.sequenceHasBeenReset()) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // When the first inflight batch
>> fails
>> > >> due to
>> > >> > > the
>> > >> > > > > > > > > truncation
>> > >> > > > > > > > > >>> case,
>> > >> > > > > > > > > >>>>> then the sequences of all the other
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // in flight batches would have been
>> > >> > restarted
>> > >> > > > from
>> > >> > > > > > the
>> > >> > > > > > > > > >>> beginning.
>> > >> > > > > > > > > >>>>> However, when those responses
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // come back from the broker, they
>> would
>> > >> also
>> > >> > > > come
>> > >> > > > > > with
>> > >> > > > > > > > an
>> > >> > > > > > > > > >>>>> UNKNOWN_PRODUCER_ID error. In this case, we
>> should
>> > >> not
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // reset the sequence numbers to the
>> > >> > beginning.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> return true;
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> } else if
>> > >> > > > > (lastAckedOffset(batch.topicPartition).orElse(
>> > >> > > > > > > > > >>>>> *NO_LAST_ACKED_SEQUENCE_NUMBER*) <
>> > >> > > > response.logStartOffset) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // The head of the log has been
>> removed,
>> > >> > > probably
>> > >> > > > > due
>> > >> > > > > > > to
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >>>>> retention time elapsing. In this case,
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // we expect to lose the producer
>> state.
>> > >> For
>> > >> > > the
>> > >> > > > > > > > > transactional
>> > >> > > > > > > > > >>>>> producer, reset the sequences of all
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // inflight batches to be from the
>> > >> beginning
>> > >> > > and
>> > >> > > > > > retry
>> > >> > > > > > > > > them,
>> > >> > > > > > > > > >>> so
>> > >> > > > > > > > > >>>>> that the transaction does not need to
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // be aborted. For the idempotent
>> > >> producer,
>> > >> > > bump
>> > >> > > > > the
>> > >> > > > > > > > epoch
>> > >> > > > > > > > > to
>> > >> > > > > > > > > >>> avoid
>> > >> > > > > > > > > >>>>> reusing (sequence, epoch) pairs
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> if (isTransactional()) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>
>> > >> > > > txnPartitionMap.startSequencesAtBeginning(batch.topicPartition,
>> > >> > > > > > > > > >>>>> this.producerIdAndEpoch);
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> } else {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > requestEpochBumpForPartition(batch.topicPartition);
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> }
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> return true;
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> }
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> if (!isTransactional()) {
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // For the idempotent producer,
>> always
>> > >> retry
>> > >> > > > > > > > > >>> UNKNOWN_PRODUCER_ID
>> > >> > > > > > > > > >>>>> errors. If the batch has the current
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> // producer ID and epoch, request a
>> bump
>> > >> of
>> > >> > the
>> > >> > > > > > epoch.
>> > >> > > > > > > > > >>> Otherwise
>> > >> > > > > > > > > >>>>> just retry the produce.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > requestEpochBumpForPartition(batch.topicPartition);
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> return true;
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> }
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> }
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> I was considering keeping this behavior — but
>> am
>> > >> open
>> > >> > to
>> > >> > > > > > > > simplifying
>> > >> > > > > > > > > >>> it.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> We are leaving changes to older clients off the
>> > >> table
>> > >> > > here
>> > >> > > > > > since
>> > >> > > > > > > it
>> > >> > > > > > > > > >>> caused
>> > >> > > > > > > > > >>>>> many issues for clients in the past. Previously
>> > this
>> > >> > was
>> > >> > > a
>> > >> > > > > > fatal
>> > >> > > > > > > > > error
>> > >> > > > > > > > > >>> and
>> > >> > > > > > > > > >>>>> we didn't have the mechanisms in place to
>> detect
>> > >> when
>> > >> > > this
>> > >> > > > > was
>> > >> > > > > > a
>> > >> > > > > > > > > >>> legitimate
>> > >> > > > > > > > > >>>>> case vs some bug or gap in the protocol.
>> Ensuring
>> > >> each
>> > >> > > > > > > transaction
>> > >> > > > > > > > > has
>> > >> > > > > > > > > >>> its
>> > >> > > > > > > > > >>>>> own epoch should close this gap.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> And to address Jeff's second point:
>> > >> > > > > > > > > >>>>> *does the typical produce request path append
>> > >> records
>> > >> > to
>> > >> > > > > local
>> > >> > > > > > > log
>> > >> > > > > > > > > >>> along*
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> *with the currentTxnFirstOffset information? I
>> > would
>> > >> > like
>> > >> > > > to
>> > >> > > > > > > > > >>> understand*
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> *when the field is written to disk.*
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> Yes, the first produce request populates this
>> > field
>> > >> and
>> > >> > > > > writes
>> > >> > > > > > > the
>> > >> > > > > > > > > >>> offset
>> > >> > > > > > > > > >>>>> as part of the record batch and also to the
>> > producer
>> > >> > > state
>> > >> > > > > > > > snapshot.
>> > >> > > > > > > > > >>> When
>> > >> > > > > > > > > >>>>> we reload the records on restart and/or
>> > >> reassignment,
>> > >> > we
>> > >> > > > > > > repopulate
>> > >> > > > > > > > > >>> this
>> > >> > > > > > > > > >>>>> field with the snapshot from disk along with
>> the
>> > >> rest
>> > >> > of
>> > >> > > > the
>> > >> > > > > > > > producer
>> > >> > > > > > > > > >>>>> state.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> Let me know if there are further comments
>> and/or
>> > >> > > questions.
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> Thanks,
>> > >> > > > > > > > > >>>>> Justine
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>> On Tue, Nov 22, 2022 at 9:00 PM Jeff Kim
>> > >> > > > > > > > > <jeff....@confluent.io.invalid
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>>> wrote:
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>>> Hi Justine,
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> Thanks for the KIP! I have two questions:
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> 1) For new clients, we can once again return
>> an
>> > >> error
>> > >> > > > > > > > > >>> UNKNOWN_PRODUCER_ID
>> > >> > > > > > > > > >>>>>> for sequences
>> > >> > > > > > > > > >>>>>> that are non-zero when there is no producer
>> state
>> > >> > > present
>> > >> > > > on
>> > >> > > > > > the
>> > >> > > > > > > > > >>> server.
>> > >> > > > > > > > > >>>>>> This will indicate we missed the 0 sequence
>> and
>> > we
>> > >> > don't
>> > >> > > > yet
>> > >> > > > > > > want
>> > >> > > > > > > > to
>> > >> > > > > > > > > >>>>> write
>> > >> > > > > > > > > >>>>>> to the log.
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> I would like to understand the current
>> behavior
>> > to
>> > >> > > handle
>> > >> > > > > > older
>> > >> > > > > > > > > >>> clients,
>> > >> > > > > > > > > >>>>>> and if there are any changes we are making.
>> Maybe
>> > >> I'm
>> > >> > > > > missing
>> > >> > > > > > > > > >>> something,
>> > >> > > > > > > > > >>>>>> but we would want to identify whether we
>> missed
>> > >> the 0
>> > >> > > > > sequence
>> > >> > > > > > > for
>> > >> > > > > > > > > >>> older
>> > >> > > > > > > > > >>>>>> clients, no?
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> 2) Upon returning from the transaction
>> > >> coordinator, we
>> > >> > > can
>> > >> > > > > set
>> > >> > > > > > > the
>> > >> > > > > > > > > >>>>>> transaction
>> > >> > > > > > > > > >>>>>> as ongoing on the leader by populating
>> > >> > > > currentTxnFirstOffset
>> > >> > > > > > > > > >>>>>> through the typical produce request handling.
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> does the typical produce request path append
>> > >> records
>> > >> > to
>> > >> > > > > local
>> > >> > > > > > > log
>> > >> > > > > > > > > >>> along
>> > >> > > > > > > > > >>>>>> with the currentTxnFirstOffset information? I
>> > would
>> > >> > like
>> > >> > > > to
>> > >> > > > > > > > > understand
>> > >> > > > > > > > > >>>>>> when the field is written to disk.
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> Thanks,
>> > >> > > > > > > > > >>>>>> Jeff
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>> On Tue, Nov 22, 2022 at 4:44 PM Artem Livshits
>> > >> > > > > > > > > >>>>>> <alivsh...@confluent.io.invalid> wrote:
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>>> Hi Justine,
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>> Thank you for the KIP. I have one question.
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>> 5) For new clients, we can once again return
>> an
>> > >> error
>> > >> > > > > > > > > >>>>> UNKNOWN_PRODUCER_ID
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>> I believe we had problems in the past with
>> > >> returning
>> > >> > > > > > > > > >>>>> UNKNOWN_PRODUCER_ID
>> > >> > > > > > > > > >>>>>>> because it was considered fatal and required
>> > >> client
>> > >> > > > > restart.
>> > >> > > > > > > It
>> > >> > > > > > > > > >>> would
>> > >> > > > > > > > > >>>>> be
>> > >> > > > > > > > > >>>>>>> good to spell out the new client behavior
>> when
>> > it
>> > >> > > > receives
>> > >> > > > > > the
>> > >> > > > > > > > > error.
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>> -Artem
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>> On Tue, Nov 22, 2022 at 10:00 AM Justine
>> Olshan
>> > >> > > > > > > > > >>>>>>> <jols...@confluent.io.invalid> wrote:
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>>> Thanks for taking a look Matthias. I've
>> tried
>> > to
>> > >> > > answer
>> > >> > > > > your
>> > >> > > > > > > > > >>>>> questions
>> > >> > > > > > > > > >>>>>>>> below:
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 10)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> Right — so the hanging transaction only
>> occurs
>> > >> when
>> > >> > we
>> > >> > > > > have
>> > >> > > > > > a
>> > >> > > > > > > > late
>> > >> > > > > > > > > >>>>>>> message
>> > >> > > > > > > > > >>>>>>>> come in and the partition is never added to
>> a
>> > >> > > > transaction
>> > >> > > > > > > again.
>> > >> > > > > > > > > If
>> > >> > > > > > > > > >>>>> we
>> > >> > > > > > > > > >>>>>>>> never add the partition to a transaction, we
>> > will
>> > >> > > never
>> > >> > > > > > write
>> > >> > > > > > > a
>> > >> > > > > > > > > >>>>> marker
>> > >> > > > > > > > > >>>>>>> and
>> > >> > > > > > > > > >>>>>>>> never advance the LSO.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> If we do end up adding the partition to the
>> > >> > > transaction
>> > >> > > > (I
>> > >> > > > > > > > suppose
>> > >> > > > > > > > > >>>>> this
>> > >> > > > > > > > > >>>>>>> can
>> > >> > > > > > > > > >>>>>>>> happen before or after the late message
>> comes
>> > in)
>> > >> > then
>> > >> > > > we
>> > >> > > > > > will
>> > >> > > > > > > > > >>>>> include
>> > >> > > > > > > > > >>>>>>> the
>> > >> > > > > > > > > >>>>>>>> late message in the next (incorrect)
>> > transaction.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> So perhaps it is clearer to make the
>> > distinction
>> > >> > > between
>> > >> > > > > > > > messages
>> > >> > > > > > > > > >>>>> that
>> > >> > > > > > > > > >>>>>>>> eventually get added to the transaction (but
>> > the
>> > >> > wrong
>> > >> > > > > one)
>> > >> > > > > > or
>> > >> > > > > > > > > >>>>> messages
>> > >> > > > > > > > > >>>>>>>> that never get added and become hanging.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 20)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> The client side change for 2 is removing the
>> > >> > > > addPartitions
>> > >> > > > > > to
>> > >> > > > > > > > > >>>>>> transaction
>> > >> > > > > > > > > >>>>>>>> call. We don't need to make this from the
>> > >> producer
>> > >> > to
>> > >> > > > the
>> > >> > > > > > txn
>> > >> > > > > > > > > >>>>>>> coordinator,
>> > >> > > > > > > > > >>>>>>>> only server side.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> In my opinion, the issue with the
>> > >> addPartitionsToTxn
>> > >> > > > call
>> > >> > > > > > for
>> > >> > > > > > > > > older
>> > >> > > > > > > > > >>>>>>> clients
>> > >> > > > > > > > > >>>>>>>> is that we don't have the epoch bump, so we
>> > don't
>> > >> > know
>> > >> > > > if
>> > >> > > > > > the
>> > >> > > > > > > > > >>> message
>> > >> > > > > > > > > >>>>>>>> belongs to the previous transaction or this
>> > one.
>> > >> We
>> > >> > > need
>> > >> > > > > to
>> > >> > > > > > > > check
>> > >> > > > > > > > > if
>> > >> > > > > > > > > >>>>>> the
>> > >> > > > > > > > > >>>>>>>> partition has been added to this
>> transaction.
>> > Of
>> > >> > > course,
>> > >> > > > > > this
>> > >> > > > > > > > > means
>> > >> > > > > > > > > >>>>> we
>> > >> > > > > > > > > >>>>>>>> won't completely cover the case where we
>> have a
>> > >> > really
>> > >> > > > > late
>> > >> > > > > > > > > message
>> > >> > > > > > > > > >>>>> and
>> > >> > > > > > > > > >>>>>>> we
>> > >> > > > > > > > > >>>>>>>> have added the partition to the new
>> > transaction,
>> > >> but
>> > >> > > > > that's
>> > >> > > > > > > > > >>>>>> unfortunately
>> > >> > > > > > > > > >>>>>>>> something we will need the new clients to
>> > cover.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 30)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> Transaction is ongoing = partition was
>> added to
>> > >> > > > > transaction
>> > >> > > > > > > via
>> > >> > > > > > > > > >>>>>>>> addPartitionsToTxn. We check this with the
>> > >> > > > > > > DescribeTransactions
>> > >> > > > > > > > > >>> call.
>> > >> > > > > > > > > >>>>>> Let
>> > >> > > > > > > > > >>>>>>>> me know if this wasn't sufficiently
>> explained
>> > >> here:
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > >
>> > >> > > > > > > >
>> > >> > > > > > >
>> > >> > > > > >
>> > >> > > > >
>> > >> > > >
>> > >> > >
>> > >> >
>> > >>
>> >
>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-890%3A+Transactions+Server-Side+Defense#KIP890:TransactionsServerSideDefense-EnsureOngoingTransactionforOlderClients(3)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 40)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> The idea here is that if any messages
>> somehow
>> > >> come
>> > >> > in
>> > >> > > > > before
>> > >> > > > > > > we
>> > >> > > > > > > > > get
>> > >> > > > > > > > > >>>>> the
>> > >> > > > > > > > > >>>>>>> new
>> > >> > > > > > > > > >>>>>>>> epoch to the producer, they will be fenced.
>> > >> However,
>> > >> > > if
>> > >> > > > we
>> > >> > > > > > > don't
>> > >> > > > > > > > > >>>>> think
>> > >> > > > > > > > > >>>>>>> this
>> > >> > > > > > > > > >>>>>>>> is necessary, it can be discussed
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 50)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> It should be synchronous because if we have
>> an
>> > >> event
>> > >> > > > (ie,
>> > >> > > > > an
>> > >> > > > > > > > > error)
>> > >> > > > > > > > > >>>>>> that
>> > >> > > > > > > > > >>>>>>>> causes us to need to abort the transaction,
>> we
>> > >> need
>> > >> > to
>> > >> > > > > know
>> > >> > > > > > > > which
>> > >> > > > > > > > > >>>>>>>> partitions to send transaction markers to.
>> We
>> > >> know
>> > >> > the
>> > >> > > > > > > > partitions
>> > >> > > > > > > > > >>>>>> because
>> > >> > > > > > > > > >>>>>>>> we added them to the coordinator via the
>> > >> > > > > addPartitionsToTxn
>> > >> > > > > > > > call.
>> > >> > > > > > > > > >>>>>>>> Previously we have had asynchronous calls in
>> > the
>> > >> > past
>> > >> > > > (ie,
>> > >> > > > > > > > writing
>> > >> > > > > > > > > >>>>> the
>> > >> > > > > > > > > >>>>>>>> commit markers when the transaction is
>> > completed)
>> > >> > but
>> > >> > > > > often
>> > >> > > > > > > this
>> > >> > > > > > > > > >>> just
>> > >> > > > > > > > > >>>>>>>> causes confusion as we need to wait for some
>> > >> > > operations
>> > >> > > > to
>> > >> > > > > > > > > complete.
>> > >> > > > > > > > > >>>>> In
>> > >> > > > > > > > > >>>>>>> the
>> > >> > > > > > > > > >>>>>>>> writing commit markers case, clients often
>> see
>> > >> > > > > > > > > >>>>> CONCURRENT_TRANSACTIONs
>> > >> > > > > > > > > >>>>>>>> error messages and that can be confusing.
>> For
>> > >> that
>> > >> > > > reason,
>> > >> > > > > > it
>> > >> > > > > > > > may
>> > >> > > > > > > > > be
>> > >> > > > > > > > > >>>>>>>> simpler to just have synchronous calls —
>> > >> especially
>> > >> > if
>> > >> > > > we
>> > >> > > > > > need
>> > >> > > > > > > > to
>> > >> > > > > > > > > >>>>> block
>> > >> > > > > > > > > >>>>>>> on
>> > >> > > > > > > > > >>>>>>>> some operation's completion anyway before we
>> > can
>> > >> > start
>> > >> > > > the
>> > >> > > > > > > next
>> > >> > > > > > > > > >>>>>>>> transaction. And yes, I meant coordinator. I
>> > will
>> > >> > fix
>> > >> > > > > that.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> 60)
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> When we are checking if the transaction is
>> > >> ongoing,
>> > >> > we
>> > >> > > > > need
>> > >> > > > > > to
>> > >> > > > > > > > > make
>> > >> > > > > > > > > >>> a
>> > >> > > > > > > > > >>>>>>> round
>> > >> > > > > > > > > >>>>>>>> trip from the leader partition to the
>> > transaction
>> > >> > > > > > coordinator.
>> > >> > > > > > > > In
>> > >> > > > > > > > > >>> the
>> > >> > > > > > > > > >>>>>>> time
>> > >> > > > > > > > > >>>>>>>> we are waiting for this message to come
>> back,
>> > in
>> > >> > > theory
>> > >> > > > we
>> > >> > > > > > > could
>> > >> > > > > > > > > >>> have
>> > >> > > > > > > > > >>>>>>> sent
>> > >> > > > > > > > > >>>>>>>> a commit/abort call that would make the
>> > original
>> > >> > > result
>> > >> > > > of
>> > >> > > > > > the
>> > >> > > > > > > > > check
>> > >> > > > > > > > > >>>>>> out
>> > >> > > > > > > > > >>>>>>> of
>> > >> > > > > > > > > >>>>>>>> date. That is why we can check the leader
>> state
>> > >> > before
>> > >> > > > we
>> > >> > > > > > > write
>> > >> > > > > > > > to
>> > >> > > > > > > > > >>>>> the
>> > >> > > > > > > > > >>>>>>> log.
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> I'm happy to update the KIP if some of these
>> > >> things
>> > >> > > were
>> > >> > > > > not
>> > >> > > > > > > > > clear.
>> > >> > > > > > > > > >>>>>>>> Thanks,
>> > >> > > > > > > > > >>>>>>>> Justine
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>> On Mon, Nov 21, 2022 at 7:11 PM Matthias J.
>> > Sax <
>> > >> > > > > > > > mj...@apache.org
>> > >> > > > > > > > > >
>> > >> > > > > > > > > >>>>>>> wrote:
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Thanks for the KIP.
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Couple of clarification questions (I am
>> not a
>> > >> > broker
>> > >> > > > > expert
>> > >> > > > > > > do
>> > >> > > > > > > > > >>>>> maybe
>> > >> > > > > > > > > >>>>>>>>> some question are obvious for others, but
>> not
>> > >> for
>> > >> > me
>> > >> > > > with
>> > >> > > > > > my
>> > >> > > > > > > > lack
>> > >> > > > > > > > > >>>>> of
>> > >> > > > > > > > > >>>>>>>>> broker knowledge).
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (10)
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> The delayed message case can also violate
>> EOS
>> > >> if
>> > >> > the
>> > >> > > > > > delayed
>> > >> > > > > > > > > >>>>>> message
>> > >> > > > > > > > > >>>>>>>>> comes in after the next addPartitionsToTxn
>> > >> request
>> > >> > > > comes
>> > >> > > > > > in.
>> > >> > > > > > > > > >>>>>>> Effectively
>> > >> > > > > > > > > >>>>>>>> we
>> > >> > > > > > > > > >>>>>>>>> may see a message from a previous (aborted)
>> > >> > > transaction
>> > >> > > > > > > become
>> > >> > > > > > > > > part
>> > >> > > > > > > > > >>>>>> of
>> > >> > > > > > > > > >>>>>>>> the
>> > >> > > > > > > > > >>>>>>>>> next transaction.
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> What happens if the message come in before
>> the
>> > >> next
>> > >> > > > > > > > > >>>>>> addPartitionsToTxn
>> > >> > > > > > > > > >>>>>>>>> request? It seems the broker hosting the
>> data
>> > >> > > > partitions
>> > >> > > > > > > won't
>> > >> > > > > > > > > know
>> > >> > > > > > > > > >>>>>>>>> anything about it and append it to the
>> > >> partition,
>> > >> > > too?
>> > >> > > > > What
>> > >> > > > > > > is
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >>>>>>>>> difference between both cases?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Also, it seems a TX would only hang, if
>> there
>> > >> is no
>> > >> > > > > > following
>> > >> > > > > > > > TX
>> > >> > > > > > > > > >>>>> that
>> > >> > > > > > > > > >>>>>>> is
>> > >> > > > > > > > > >>>>>>>>> either committer or aborted? Thus, for the
>> > case
>> > >> > > above,
>> > >> > > > > the
>> > >> > > > > > TX
>> > >> > > > > > > > > might
>> > >> > > > > > > > > >>>>>>>>> actually not hang (of course, we might get
>> an
>> > >> EOS
>> > >> > > > > violation
>> > >> > > > > > > if
>> > >> > > > > > > > > the
>> > >> > > > > > > > > >>>>>>> first
>> > >> > > > > > > > > >>>>>>>>> TX was aborted and the second committed, or
>> > the
>> > >> > other
>> > >> > > > way
>> > >> > > > > > > > > around).
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (20)
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> Of course, 1 and 2 require client-side
>> > >> changes, so
>> > >> > > for
>> > >> > > > > > older
>> > >> > > > > > > > > >>>>>> clients,
>> > >> > > > > > > > > >>>>>>>>> those approaches won’t apply.
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> For (1) I understand why a client change is
>> > >> > > necessary,
>> > >> > > > > but
>> > >> > > > > > > not
>> > >> > > > > > > > > sure
>> > >> > > > > > > > > >>>>>> why
>> > >> > > > > > > > > >>>>>>>>> we need a client change for (2). Can you
>> > >> elaborate?
>> > >> > > --
>> > >> > > > > > Later
>> > >> > > > > > > > you
>> > >> > > > > > > > > >>>>>>> explain
>> > >> > > > > > > > > >>>>>>>>> that we should send a
>> > >> DescribeTransactionRequest,
>> > >> > > but I
>> > >> > > > > am
>> > >> > > > > > > not
>> > >> > > > > > > > > sure
>> > >> > > > > > > > > >>>>>>> why?
>> > >> > > > > > > > > >>>>>>>>> Can't we not just do an implicit
>> > >> AddPartiitonToTx,
>> > >> > > too?
>> > >> > > > > If
>> > >> > > > > > > the
>> > >> > > > > > > > > old
>> > >> > > > > > > > > >>>>>>>>> producer correctly registered the partition
>> > >> > already,
>> > >> > > > the
>> > >> > > > > > > > > >>>>>> TX-coordinator
>> > >> > > > > > > > > >>>>>>>>> can just ignore it as it's an idempotent
>> > >> operation?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (30)
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> To cover older clients, we will ensure a
>> > >> > transaction
>> > >> > > > is
>> > >> > > > > > > > ongoing
>> > >> > > > > > > > > >>>>>>> before
>> > >> > > > > > > > > >>>>>>>>> we write to a transaction
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Not sure what you mean by this? Can you
>> > >> elaborate?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (40)
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> [the TX-coordinator] will write the
>> prepare
>> > >> commit
>> > >> > > > > message
>> > >> > > > > > > > with
>> > >> > > > > > > > > a
>> > >> > > > > > > > > >>>>>>>> bumped
>> > >> > > > > > > > > >>>>>>>>> epoch and send WriteTxnMarkerRequests with
>> the
>> > >> > bumped
>> > >> > > > > > epoch.
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Why do we use the bumped epoch for both? It
>> > >> seems
>> > >> > > more
>> > >> > > > > > > > intuitive
>> > >> > > > > > > > > to
>> > >> > > > > > > > > >>>>>> use
>> > >> > > > > > > > > >>>>>>>>> the current epoch, and only return the
>> bumped
>> > >> epoch
>> > >> > > to
>> > >> > > > > the
>> > >> > > > > > > > > >>>>> producer?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (50) "Implicit AddPartitionToTransaction"
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Why does the implicitly sent request need
>> to
>> > be
>> > >> > > > > > synchronous?
>> > >> > > > > > > > The
>> > >> > > > > > > > > >>>>> KIP
>> > >> > > > > > > > > >>>>>>>>> also says
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> in case we need to abort and need to know
>> > which
>> > >> > > > > partitions
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> What do you mean by this?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> we don’t want to write to it before we
>> store
>> > in
>> > >> > the
>> > >> > > > > > > > transaction
>> > >> > > > > > > > > >>>>>>> manager
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> Do you mean TX-coordinator instead of
>> > "manager"?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> (60)
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> For older clients and ensuring that the TX
>> is
>> > >> > > ongoing,
>> > >> > > > > you
>> > >> > > > > > > > > >>>>> describe a
>> > >> > > > > > > > > >>>>>>>>> race condition. I am not sure if I can
>> follow
>> > >> here.
>> > >> > > Can
>> > >> > > > > you
>> > >> > > > > > > > > >>>>>> elaborate?
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> -Matthias
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>> On 11/18/22 1:21 PM, Justine Olshan wrote:
>> > >> > > > > > > > > >>>>>>>>>> Hey all!
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> I'd like to start a discussion on my
>> proposal
>> > >> to
>> > >> > add
>> > >> > > > > some
>> > >> > > > > > > > > >>>>>> server-side
>> > >> > > > > > > > > >>>>>>>>>> checks on transactions to avoid hanging
>> > >> > > transactions.
>> > >> > > > I
>> > >> > > > > > know
>> > >> > > > > > > > > this
>> > >> > > > > > > > > >>>>>> has
>> > >> > > > > > > > > >>>>>>>>> been
>> > >> > > > > > > > > >>>>>>>>>> an issue for some time, so I really hope
>> this
>> > >> KIP
>> > >> > > will
>> > >> > > > > be
>> > >> > > > > > > > > helpful
>> > >> > > > > > > > > >>>>>> for
>> > >> > > > > > > > > >>>>>>>>> many
>> > >> > > > > > > > > >>>>>>>>>> users of EOS.
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> The KIP includes changes that will be
>> > >> compatible
>> > >> > > with
>> > >> > > > > old
>> > >> > > > > > > > > clients
>> > >> > > > > > > > > >>>>>> and
>> > >> > > > > > > > > >>>>>>>>>> changes to improve performance and
>> > correctness
>> > >> on
>> > >> > > new
>> > >> > > > > > > clients.
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> Please take a look and leave any comments
>> you
>> > >> may
>> > >> > > > have!
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> KIP:
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > >
>> > >> > > > > > > >
>> > >> > > > > > >
>> > >> > > > > >
>> > >> > > > >
>> > >> > > >
>> > >> > >
>> > >> >
>> > >>
>> >
>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-890%3A+Transactions+Server-Side+Defense
>> > >> > > > > > > > > >>>>>>>>>> JIRA:
>> > >> > > > https://issues.apache.org/jira/browse/KAFKA-14402
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>> Thanks!
>> > >> > > > > > > > > >>>>>>>>>> Justine
>> > >> > > > > > > > > >>>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>>
>> > >> > > > > > > > > >>>>>>>>
>> > >> > > > > > > > > >>>>>>>
>> > >> > > > > > > > > >>>>>>
>> > >> > > > > > > > > >>>>>
>> > >> > > > > > > > > >>>>
>> > >> > > > > > > > > >>>
>> > >> > > > > > > > > >>
>> > >> > > > > > > > > >
>> > >> > > > > > > > >
>> > >> > > > > > > >
>> > >> > > > > > >
>> > >> > > > > >
>> > >> > > > >
>> > >> > > >
>> > >> > >
>> > >> >
>> > >>
>> > >
>> >
>>
>
