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https://issues.apache.org/jira/browse/FLINK-8117?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16260475#comment-16260475
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ASF GitHub Bot commented on FLINK-8117:
---------------------------------------
GitHub user ggevay opened a pull request:
https://github.com/apache/flink/pull/5041
[FLINK-8117] [runtime] [streaming] Eliminate modulo operation from round
robin partitioners
## What is the purpose of the change
This PR changes `RebalancePartitioner`, `RescalePartitioner`, and
`RoundRobinChannelSelector` to not use `%` for wrapping around when reaching
the number of channels, but use an `if`-statement instead.
## Brief change log
- Make the above change in `RebalancePartitioner`, `RescalePartitioner`,
and `RoundRobinChannelSelector`
- Additionally, I added `final` to the field that is holding the reused
return array in `RebalancePartitioner`, `RoundRobinChannelSelector`,
`ShufflePartitioner`, `ForwardPartitioner`, `GlobalPartitioner`,
`CustomPartitionerWrapper`.
## Verifying this change
This change is already covered by existing tests, such as
`RebalancePartitionerTest`, `RescalePartitionerTest`.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): no
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: no
- The serializers: no
- The runtime per-record code paths (performance sensitive): **yes**
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Yarn/Mesos, ZooKeeper: no
- The S3 file system connector: no
## Documentation
- Does this pull request introduce a new feature? no
- If yes, how is the feature documented? not applicable
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/ggevay/flink round-robin-no-modulo
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/flink/pull/5041.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #5041
----
commit 04ff7134e3e5fc750b6f94a385a3ff3bfd921fa3
Author: Gabor Gevay <gga...@gmail.com>
Date: 2017-11-20T14:12:17Z
[FLINK-8117] [runtime] [streaming] Eliminate modulo operation from
round-robin partitioners
----
> Eliminate modulo operation from RoundRobinChannelSelector and
> RebalancePartitioner
> ----------------------------------------------------------------------------------
>
> Key: FLINK-8117
> URL: https://issues.apache.org/jira/browse/FLINK-8117
> Project: Flink
> Issue Type: Improvement
> Components: Local Runtime, Streaming
> Reporter: Gabor Gevay
> Assignee: Gabor Gevay
> Priority: Minor
> Labels: performance
> Fix For: 1.5.0
>
>
> {{RoundRobinChannelSelector}}, {{RebalancePartitioner}}, and
> {{RescalePartitioner}} use a modulo operation to wrap around when the current
> channel counter reaches the number of channels. Using an {{if}} would have
> better performance.
> A division with 32 bit operands is ~25 cycles on modern Intel CPUs \[1\], but
> the {{if}} will be only 1-2 cycles on average, since the branch predictor can
> most of the time predict the condition to be false.
> \[1\] http://www.agner.org/optimize/instruction_tables.pdf
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