squah-confluent commented on PR #20055:
URL: https://github.com/apache/kafka/pull/20055#issuecomment-3017816001
* I "optimized" away a transition to `UNREVOKED_PARTITIONS` when the
subscription has changed, but the client doesn't own the revoked partitions
anyway. This makes the client re-enter the `STABLE` state 1 heartbeat sooner.
It adds a `ownsRevokedPartitions` call, which has a small performance hit
(compare `stableToUnrevokedPartitionsWithSubscriptionChange` and
`stableToStableWithSubscriptionChange` in the benchmarks below).
* I discovered an interesting behavior when transitioning away from
`UNREVOKED_PARTITIONS`. When the target assignment contains a partition that
was previously pending revocation, the member enters the
`UNRELEASED_PARTITIONS` state, as if another member was holding the partition.
On the next reconcile, I think there is no issue. I haven't tried to fix this
behavior since it existed before this PR.
I reran the benchmarks with the largest parameter sizes:
```
Benchmark
(partitionsPerTopic) (topicCount) Mode Cnt Score Error Units
CurrentAssignmentBuilderBenchmark.stableToStableWithNewTargetAssignment
50 1000 avgt 2.771 ms/op
CurrentAssignmentBuilderBenchmark.stableToStableWithNoChange
50 1000 avgt ≈ 10⁻⁶ ms/op
CurrentAssignmentBuilderBenchmark.stableToStableWithSubscriptionChange
50 1000 avgt 0.046 ms/op
CurrentAssignmentBuilderBenchmark.stableToUnrevokedPartitionsWithSubscriptionChange
50 1000 avgt 0.059 ms/op
JMH benchmarks done
```
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