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From "Pavel Yaskevich (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3623) use MMapedBuffer in CompressedSegmentedFile.getSegment
Date Thu, 26 Jan 2012 15:20:39 GMT


Pavel Yaskevich commented on CASSANDRA-3623:

I'm still don't think that this is a good idea because tests don't how any significant improvement
in performance and Java still has very limited arsenal of functionality to work with mmap'ed
files, program doesn't have a full control over ByteBufferes sharing mmapp'ed memory which
could lead to problems like CASSANDRA-3179.

By the way, Vijay, maybe you weren't dropping page cache between tests? Let's see what Yuki
has to say.
> use MMapedBuffer in CompressedSegmentedFile.getSegment
> ------------------------------------------------------
>                 Key: CASSANDRA-3623
>                 URL:
>             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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