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From "Pavel Yaskevich (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3623) use MMapedBuffer in CompressedSegmentedFile.getSegment
Date Wed, 04 Jan 2012 16:03:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13179585#comment-13179585
] 

Pavel Yaskevich commented on CASSANDRA-3623:
--------------------------------------------

This is not so surprising for me in the situation when work-set does not fit into memory,
which is not a rate case, I have expected mapped I/O to be slightly better, I also wanted
to mention that although patch don't copy from kernelspace to userspace it does buffer duplication
which means higher object allocation rates which would affect performance.
                
> use MMapedBuffer in CompressedSegmentedFile.getSegment
> ------------------------------------------------------
>
>                 Key: CASSANDRA-3623
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3623
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.1
>            Reporter: Vijay
>            Assignee: Vijay
>              Labels: compression
>             Fix For: 1.1
>
>         Attachments: 0001-MMaped-Compression-segmented-file-v2.patch, 0001-MMaped-Compression-segmented-file-v3.patch,
0001-MMaped-Compression-segmented-file.patch, 0002-tests-for-MMaped-Compression-segmented-file-v2.patch,
0002-tests-for-MMaped-Compression-segmented-file-v3.patch, CRC+MMapIO.xlsx, MMappedIO-Performance.docx
>
>
> CompressedSegmentedFile.getSegment seem to open a new file and doesnt seem to use the
MMap and hence a higher CPU on the nodes and higher latencies on reads. 
> This ticket is to implement the TODO mentioned in CompressedRandomAccessReader
> // TODO refactor this to separate concept of "buffer to avoid lots of read() syscalls"
and "compression buffer"
> but i think a separate class for the Buffer will be better.

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