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From "Pavel Yaskevich (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3623) use MMapedBuffer in CompressedSegmentedFile.getSegment
Date Fri, 23 Dec 2011 23:54:30 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13175626#comment-13175626
] 

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

The problem is that you can't remove duplicate() because the same segment can be requested
concurrently by different reads and we don't want to limit concurrency with synchronisation
over segment use.
                
> 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.patch,
0002-tests-for-MMaped-Compression-segmented-file-v2.patch
>
>
> 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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