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https://issues.apache.org/jira/browse/CASSANDRA-15229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17101139#comment-17101139
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Josh McKenzie commented on CASSANDRA-15229:
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If it's not too much bother, could we update the Since Version on this and add
a little detail in the description as to the impact of this regression on the
system?
> BufferPool Regression
> ---------------------
>
> Key: CASSANDRA-15229
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15229
> Project: Cassandra
> Issue Type: Bug
> Components: Local/Caching
> Reporter: Benedict Elliott Smith
> Assignee: ZhaoYang
> Priority: Normal
> Fix For: 4.0, 4.0-beta
>
> Attachments: 15229-count.png, 15229-direct.png, 15229-hit-rate.png,
> 15229-recirculate-count.png, 15229-recirculate-hit-rate.png,
> 15229-recirculate-size.png, 15229-recirculate.png, 15229-size.png,
> 15229-unsafe.png
>
>
> The BufferPool was never intended to be used for a {{ChunkCache}}, and we
> need to either change our behaviour to handle uncorrelated lifetimes or use
> something else. This is particularly important with the default chunk size
> for compressed sstables being reduced. If we address the problem, we should
> also utilise the BufferPool for native transport connections like we do for
> internode messaging, and reduce the number of pooling solutions we employ.
> Probably the best thing to do is to improve BufferPool’s behaviour when used
> for things with uncorrelated lifetimes, which essentially boils down to
> tracking those chunks that have not been freed and re-circulating them when
> we run out of completely free blocks. We should probably also permit
> instantiating separate {{BufferPool}}, so that we can insulate internode
> messaging from the {{ChunkCache}}, or at least have separate memory bounds
> for each, and only share fully-freed chunks.
> With these improvements we can also safely increase the {{BufferPool}} chunk
> size to 128KiB or 256KiB, to guarantee we can fit compressed pages and reduce
> the amount of global coordination and per-allocation overhead. We don’t need
> 1KiB granularity for allocations, nor 16 byte granularity for tiny
> allocations.
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