[jira] [Updated] (CASSANDRA-6609) Reduce Bloom Filter Garbage Allocation

["Benedict (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-6609?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

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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