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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11940) Look into better default file_cache_size for 2.2
Date Fri, 17 Jun 2016 14:28:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15336209#comment-15336209
] 

T Jake Luciani commented on CASSANDRA-11940:
--------------------------------------------

I think this is actually the same issue as CASSANDRA-8729

Recycling the Mapped byte buffer is causing read before write.

> Look into better default file_cache_size for 2.2
> ------------------------------------------------
>
>                 Key: CASSANDRA-11940
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11940
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: T Jake Luciani
>            Assignee: T Jake Luciani
>             Fix For: 2.2.x
>
>         Attachments: abnormal disk read throughput.png
>
>
> CASSANDRA-8464 added support for mmapped decompression where in version <= 2.1 the
reads were all decompressed in standard heap buffers.
> Since the usage of the file_cache is based solely on the buffer capacity we should/can
make this much larger in 2.2 when the disk access mode is mmap.  
> The downside of this cache being too small is made worse by 8464 since the buffers are
mmapped/unmapped causing explicit page faults.



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