Hi Nikita,
I've checked out your branch, looked through the changes and run
IgniteBaselineNodeLeaveExchangeTest. Some thoughts:
1. First of all, there's fundamental issue that backup and primary
partitions behave differently:
- On primary, updating transaction needs to own exclusive lock (be on
top of GridCacheMapEntry#localCandidates queue) on key object for the
whole prepare-commit cycle. That's how two-phase commit works in Ignite.
- Primary node generates update counter via
PartitionTxUpdateCounterImpl#reserve, while backup receives update and
just applies it with provided counter.
So, if we'll perform PME in non-distributed way, we'll lose
happen-before guarantees between updates of transactions mapped on
previous topology and ones that are mapped to new topology. This may
cause the following issues:
- New primary node may start behaving as primary (spawn DHT transaction
instances and acquire exclusive locks) but still may receive updates
from previous primary. I don't know how to handle these updates
correctly as they may conflict with new updates and locks.
- New primary node should start generating update counters, but it
actually doesn't know last update counter in cluster. If it
optimistically will start from last known counter, partition consistency
may break in case updates with actual last update counter will arrive (I
guess, this issue should be reproduced as LWM > HWM assertion error).
2. According to current state of your test, testBltServerLeaveUnderLoad
is called only with PickKeyOption#NO_DATA_ON_LEAVING_NODE (which means
backups that are promoted to primaries without global synchronization
are not affected by transactional load). However, it still fails with
LWM > HWM assertion. I guess, there are another details in new partition
counters implementation that require global happen-before between
updates of transactions that are mapped to different topology versions.
Alex S,
backups that are promoted to primaries without global synchronization
are not affected by transactional load
test still fails with LWM > HWM assertion
Do you have any ideas why this may happen?
New primary node should start generating update counters, but it
actually doesn't know last update counter in cluster. If it
optimistically will start from last known counter, partition
consistency may break in case updates with actual last update counter
will arrive (I guess, this issue should be reproduced as LWM > HWM
assertion error).
How do you think, does this problem looks solvable?
Alex S and Alex G,
New primary node may start behaving as primary (spawn DHT transaction
instances and acquire exclusive locks) but still may receive updates
from previous primary. I don't know how to handle these updates
correctly as they may conflict with new updates and locks.
How do you think, can we overcome this limitation with our existing
implementation of transactions?
Best Regards,
Ivan Rakov
On 01.07.2019 11:13, Nikita Amelchev wrote:
Hi, Igniters.
I'm working on the implementation of lightweight PME for a baseline
node leave case. [1] In my implementation, each node recalculates a
new affinity and completes PME locally without distributed
communication. This is possible because there are all partitions are
distributed according to the baseline topology. And I found two
possible blockers to do it without blocking updates:
1. Finalize partitions counter. It seems that we can't correctly
collect gaps and process them without completing all txs. See the
GridDhtPartitionTopologyImpl#finalizeUpdateCounters method.
2. Apply update counters. We can't correctly set HWM counter if
primary left the cluster and sent updates to part of backups. Such
updates can be processed later and break guarantee that LWM<=HWM.
Is it impossible to leave a baseline node without waiting for all txs completed?
1. https://issues.apache.org/jira/browse/IGNITE-9913
ср, 5 июн. 2019 г. в 12:15, Nikita Amelchev <nsamelc...@gmail.com>:
Maksim,
I agree with you that we should implement current issue and do not
allow lightweight PME if there are MOVING partitions in the cluster.
But now I'm investigating issue about finalizing update counters cause
it assumes that finalizing happens on exchange and all cache updates
are completed. Here we can wrong process update counters gaps and
break recently merged IGNITE-10078.
And about phase 2, correct me if I misunderstood you.
You suggest do not move primary partitions on rebalancing completing
(do not change affinity assignment)? In this case, nodes recently join
to cluster will not have primary partitions and won't get a load after
rebalancing.
чт, 30 мая 2019 г. в 19:55, Maxim Muzafarov <maxmu...@gmail.com>:
Igniters,
I've looked through Nikita's changes and I think for the current issue
[1] we should not allow the existence of MOVING partitions in the
cluster (it must be stable) to run the lightweight PME on BLT node
leave event occurred to achieve truly unlocked operations and here are
my thoughts why.
In general, as Nikita mentioned above, the existence of MOVING
partitions in the cluster means that the rebalance procedure is
currently running. It owns cache partitions locally and sends in the
background (with additional timeout) the actual statuses of his local
partitions to the coordinator node. So, we will always have a lag
between local node partition states and all other cluster nodes
partitions states. This lag can be very huge since previous
#scheduleResendPartitions() is cancelled when a new cache group
rebalance finished. Without the fair partition states synchronization
(without full PME) and in case of local affinity recalculation on BLT
node leave event, other nodes will mark such partitions LOST in most
of the cases, which in fact are present in the cluster and saved on
some node under checkpoint. I see that it cannot be solved by saving
transition states of such partitions on each node.
As for the case when the coordinator will calculate affinity and send
"full map" to other nodes, I think it is better here to focus on
designing a new lightweight PME when the rebalancing process finishes.
Сurrently full distributed PME will occur anyway by the coordinator by
sending CacheAffinityChaneMessage, but I think we can avoid it here,
since no new MOVING or OWNING node partition states are introduced and
all the previous mappings are still valid. We don't need a distributed
PME if we will leave partition primaries on those nodes where they
were, just set correct partition statuses via a light discovery
message.
So, my plan here can be:
Phase 1. Lightweight PME on BLT node leave on a stable cluster (no
MOVING partitions);
Phase 2. Lightweight PME on BLT node finishes its rebalance procedure.
Folks, Nikita,
WDYT?
[1] https://issues.apache.org/jira/browse/IGNITE-9913
On Fri, 24 May 2019 at 13:31, Nikita Amelchev <nsamelc...@gmail.com> wrote:
Hello, Igniters!
I am working on the implementation of lightweight PME for the case of
a BLT node leave. [1]
There is a question: whether to allow lightweight PME if the cluster
has MOVING partitions?
The problems that may happen if allow:
- Nodes can differently select the primary node from current OWNING backups.
- One part of nodes can mark a partition as LOST and another one as OWNING.
We can take states of the partitions from the node2part map. The root
cause of those problems is that when rebalancing ends (get the last
message), it updates partition state of the local node to OWNING (and
schedules partitions resend). This may lead to different affinity
re-calculations on nodes.
I see two solutions:
1. Nodes will store “moving-owning” transition of partitions state
until the rebalancing ends. Each node will locally recalculate the
affinity on node left event.
2. The coordinator will calculate affinity and send "full map" to
nodes. In this case, nodes still should wait for topology change event
(to get correct topology in discovery).
If disallow lightweight PME when the cluster has MOVING partitions -
there are no problems and it works fine.
Any thoughts?
1. https://issues.apache.org/jira/browse/IGNITE-9913
пт, 29 мар. 2019 г. в 15:00, Nikita Amelchev <nsamelc...@gmail.com>:
Pavel,
I have provided MTCGA bot status in Jira issue comments. [1]
Eduard,
Yes, for current implementation it will be distributed PME if
in-memory caches configured.
1. https://issues.apache.org/jira/browse/IGNITE-9913
пт, 29 мар. 2019 г. в 14:49, Eduard Shangareev <eduard.shangar...@gmail.com>:
Nikita,
It sounds cool. But I didn't get about in-memory caches. The baseline is
not used for their affinity calculation.
So, this improvement would be switched off for them or completely (when
such caches are presented), wouldn't it?
On Thu, Mar 28, 2019 at 3:14 PM Pavel Kovalenko <jokse...@gmail.com> wrote:
Hi Nikita,
Thank you for your work. This is great improvement. I'll take look on it in
next couple of days. Could you please run TC and provide MTCGA bot status
about this change?
чт, 28 мар. 2019 г. в 14:29, Nikita Amelchev <nsamelc...@gmail.com>:
Hello, Igniters!
I have implemented lightweight version of partitions map exchange for
the case when the baseline node leaves topology. [1]
If partitions are assigned according to the baseline topology and
server node leaves there's no actual need to perform distributed PME.
Every cluster will recalculate new affinity assignments and partition
states locally. There is no need to wait for partitions released and
PME will be started immediately.
I have benchmarked duration of PME under yardstick load. PME duration
was decreased up to 10 times and the maximum latency of transactions
was decreased up to 4-5 times. See details in Jira issue comments. [1]
Could some expert of PME take a look at my changes? [2]
1. https://issues.apache.org/jira/browse/IGNITE-9913
2. https://reviews.ignite.apache.org/ignite/review/IGNT-CR-1027
--
Best wishes,
Amelchev Nikita
--
Best wishes,
Amelchev Nikita
--
Best wishes,
Amelchev Nikita
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Best wishes,
Amelchev Nikita
