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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8897) Remove FileCacheService, instead pooling the buffers
Date Sun, 24 May 2015 07:59:17 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8897?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14557670#comment-14557670
] 

Benedict commented on CASSANDRA-8897:
-------------------------------------

It would be nice to run some tests that show this change's strengths: if you disable auto-compaction
on cstar (not sure if you can do this), and make the memtable size very small, then we can
produce a workload with many sstables that still fit in memory. If we aim to write say 4G
of data, but perhaps with many overwrites so each operation has to touch multiple files (so
perhaps only 400M of data written 10 times, or 4G of data with 10+ clustering values, written
with visits=fixed(10)). If we set the memtable size to <= 100Mb, this will likely result
in files of <= 30Mb, giving us 120+ sstables. If we constrain the size of the file cache
to just 64Mb, say, we should on a random read workload see much more GC activity under the
old scheme, and likely reduced throughput.

> Remove FileCacheService, instead pooling the buffers
> ----------------------------------------------------
>
>                 Key: CASSANDRA-8897
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8897
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Stefania
>             Fix For: 3.x
>
>         Attachments: 9240_test_results.txt, snapshot-1431582436640-cpu-backtraces.png,
snapshot-1431582436640-cpu-calltree-compression-8897.nps, snapshot-1431582436640-cpu-calltree-compression-trunk.nps
>
>
> After CASSANDRA-8893, a RAR will be a very lightweight object and will not need caching,
so we can eliminate this cache entirely. Instead we should have a pool of buffers that are
page-aligned.



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