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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11301) Non-obsoleting compaction operations over compressed files can impose rate limit on normal reads
Date Wed, 09 Mar 2016 09:36:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15186845#comment-15186845
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Benedict commented on CASSANDRA-11301:
--------------------------------------

I would suggest simply corroborating via unit test that prior to this patch recycling a throttled
reader permits getting one from the pool, and with the patch this does not happen.

A live running system would be able to accumulate many such throttled readers over a long
enough time, and over many sstables.  If you were to perform a stress workload with tiny tiny
sstables (a few MB), no auto compaction, followed by several validation compactions and a
compaction throughput of 1MB you'd probably elicit the bug directly, but that's all probably
a lot of wasted effort.

> Non-obsoleting compaction operations over compressed files can impose rate limit on normal
reads
> ------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-11301
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11301
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Stefania
>             Fix For: 2.2.6
>
>
> Broken by CASSANDRA-9240; the rate limiting reader passes the ICompressedFile interface
to its parent, which uses this to attach an "owner" - which means the reader gets recycled
on close, i.e. pooled, for normal use. If the compaction were to replace the sstable there
would be no problem, which is presumably why this hasn't been encountered frequently. However
validation compactions on long lived sstables would permit these rate limited readers to accumulate.



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