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https://issues.apache.org/jira/browse/FLINK-29402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17620861#comment-17620861
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Yuan Mei commented on FLINK-29402:
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[~donaschmi]
* I understand enabling/disabling DirectIO leads to different performance
results. That seems obvious because of page caching.
* Wondering whether this option is introduced purely for benchmarking or
research performance testing?
* If yes, I would be hesitant to introduce a new option purely for testing
purposes. I share the same concern as Yun Tang.
* Rocksdb Configuration options have already been complicated, and we should
not introduce more to confuse normal users if not having to.
> Add USE_DIRECT_READ configuration parameter for RocksDB
> -------------------------------------------------------
>
> Key: FLINK-29402
> URL: https://issues.apache.org/jira/browse/FLINK-29402
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / State Backends
> Affects Versions: 1.16.0
> Reporter: Donatien
> Priority: Not a Priority
> Labels: Enhancement, pull-request-available, rocksdb
> Fix For: 1.17.0
>
> Attachments: directIO-performance-comparison.png
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> RocksDB allows the use of DirectIO for read operations to bypass the Linux
> Page Cache. To understand the impact of Linux Page Cache on performance, one
> can run a heavy workload on a single-tasked Task Manager with a container
> memory limit identical to the TM process memory. Running this same workload
> on a TM with no container memory limit will result in better performances but
> with the host memory exceeding the TM requirement.
> Linux Page Cache are of course useful but can give false results when
> benchmarking the Managed Memory used by RocksDB. DirectIO is typically
> enabled for benchmarks on working set estimation [Zwaenepoel et
> al.|[https://arxiv.org/abs/1702.04323].]
> I propose to add a configuration key allowing users to enable the use of
> DirectIO for reads thanks to the RocksDB API. This configuration would be
> disabled by default.
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