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https://issues.apache.org/jira/browse/CASSANDRA-6609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13878354#comment-13878354
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Benedict commented on CASSANDRA-6609:
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bq. patch that reduces garbage by a factor of 6
Regrettably, no. This is only the bloom filter garbage, and I actually
overstated - that's closer to the max savings as things stand. Probably closer
to factor of 2-3 on average. Depends on number of bloom hashes we use. I only
performed an isolated test of reads from a bloom filter, I haven't looked at
impact on a C* instance.
Still, I think it's a worthwhile tradeoff, but a bit of tweaking will probably
get us closer to original performance. I'd like to also figure out why the
long[] for hash() is also not being stack allocated. It definitely should be.
We shouldn't be allocating any garbage at all for this loop.
> Reduce Bloom Filter Garbage Allocation
> --------------------------------------
>
> Key: CASSANDRA-6609
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6609
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Benedict
> Attachments: tmp.diff
>
>
> Just spotted that we allocate potentially large amounts of garbage on bloom
> filter lookups, since we allocate a new long[] for each hash() and to store
> the bucket indexes we visit, in a manner that guarantees they are allocated
> on heap. With a lot of sstables and many requests, this could easily be
> hundreds of megabytes of young gen churn per second.
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