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https://issues.apache.org/jira/browse/CASSANDRA-6609?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benedict updated CASSANDRA-6609:
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Attachment: tmp.diff
I've attached a quick and simple patch that reduces garbage by a factor of 6,
but also slightly increases a bloom filter lookup cost (600ns to 750ns,
approximately). This is suboptimal, and I'm not necessarily suggesting we use
this patch as it stands. I attempted to coax the VM to allocate the arrays on
heap so we can still benefit from whatever loop unrolling optimisations are
kicking in with the original code, but I failed in my initial attempt. I will
have another look at it again soon to see if we can get the best of both worlds.
> 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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