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https://issues.apache.org/jira/browse/BEAM-11051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17548964#comment-17548964
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Danny McCormick commented on BEAM-11051:
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This issue has been migrated to https://github.com/apache/beam/issues/20574
> Python SDK harness's UnboundedThreadPoolExecutor performs poorly with slow
> DoFns
> --------------------------------------------------------------------------------
>
> Key: BEAM-11051
> URL: https://issues.apache.org/jira/browse/BEAM-11051
> Project: Beam
> Issue Type: Bug
> Components: sdk-py-harness
> Affects Versions: 2.18.0, 2.19.0, 2.20.0, 2.21.0, 2.22.0, 2.23.0, 2.24.0
> Reporter: Peter Sobot
> Priority: P3
>
> Beam jobs with slow, memory-hungry, or otherwise resource-intensive DoFn
> implementations perform quite poorly (or even OOM) due to the fact that an
> {{[UnboundedThreadPoolExecutor|https://github.com/apache/beam/blob/master/sdks/python/apache_beam/utils/thread_pool_executor.py#L89]}}
> is used to spawn workers.
> The Python SDK no longer seems to have any methods by which to control
> concurrent execution of user code. Resource-intensive DoFns can control their
> own execution by maintaining their own semaphores, but that causes input
> elements to effectively spool in-memory, with one thread created for every
> new message. If the input rate of data to a worker exceeds the worker's
> ability to process those messages, an unbounded number of threads will be
> spawned to handle incoming work.
> Versions of Beam before 2.18 allowed specifying the --worker_threads
> experimental flag to control concurrency more effectively, but that was
> [removed in November of 2019|https://github.com/apache/beam/pull/10123] by
> [[email protected]] (see: BEAM-8151).
> One possible solution would be to re-introduce a limit on the size of the
> {{_SharedUnboundedThreadPoolExecutor}} to ensure that we don't create too
> many threads, but I'm unsure of what kind of backpressure this would create
> and what effect it may have on the rest of the harness.
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