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https://issues.apache.org/jira/browse/FLINK-15368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17007221#comment-17007221
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Yu Li commented on FLINK-15368:
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Thanks for the efforts and update [~yunta]! Below are some comments and
suggestions according to the testing output and investigation result:
# We should write explicitly in our document not to set
{{optimizeForPointLookup}} when enabling RocksDB memory control.
# We cannot rely on {{strict_capacity_limit}} until
[RocksDB#6247|https://github.com/facebook/rocksdb/issues/6247] is resolved. In
another word, since the issue on {{strict_capacity_limit}} could hardly be
resolved soon, we need to work out a work-around solution for 1.10 release.
# From the [RocksDB document of
WriteBufferManager|https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager]
it should be able to limit the total memory of memtables. More specific, the
document says "a flush will be triggered if total mutable memtable size exceeds
90% of the limit". However, from the
[implementation|https://github.com/facebook/rocksdb/blob/e8263dbdaad0546c54bddd01a8454c2e750a86c2/include/rocksdb/write_buffer_manager.h#L55]
we could tell it's not following the document (write buffer could go up to
150% of the size), which is really a surprise.
# Based on the fact of #2 and #3, I suggest we work around by doing an internal
computation and setting the size of {{Cache}} and {{WriteBufferManager}}
accordingly: assume the memory limit is {{N}} and the write ratio is R, we have
{{1.5*size_of_write_buffer_manager=R*size_of_cache}},
{{1.5*size_of_write_buffer_manager+size_of_others=N}}, and
{{size_of_write_buffer_manager+size_of_others=size_of_cache}}, then we know
{{size_of_write_buffer_manager=2NR/(3+R)}} and {{size_of_cache=3N/(3+R)}}
# For the additional cost of pinned iterator and/or index, it should be
relatively small, and if it indeed cause out-of-memory, we suggest to use
{{taskmanager.memory.task.offheap}} to cover this part.
# Note that we will be able to get rid of the kind-of-complicated work-around
right after the rocksdb bug is fixed.
What do you think?
[~sewen] please also shed some lights here, thanks.
> Add end-to-end test for controlling RocksDB memory usage
> --------------------------------------------------------
>
> Key: FLINK-15368
> URL: https://issues.apache.org/jira/browse/FLINK-15368
> Project: Flink
> Issue Type: Sub-task
> Components: Runtime / State Backends
> Affects Versions: 1.10.0
> Reporter: Yu Li
> Assignee: Yun Tang
> Priority: Critical
> Fix For: 1.10.0
>
>
> We need to add an end-to-end test to make sure the RocksDB memory usage
> control works well, especially under the slot sharing case.
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