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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5863) In process (uncompressed) page cache
Date Mon, 29 Feb 2016 00:29:18 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15171263#comment-15171263
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Pavel Yaskevich commented on CASSANDRA-5863:
--------------------------------------------

I've been working on Windmill [1], recently, and it contains a page cache implementation that
may be useful here or could be used as a reference. The implementation is similar to the Linux
Kernel’s; It is based on a static, fixed maximum length Radix Tree [2] and supports asynchronous
reads and writes using a dedicated thread pool. I’ve recently added DMA support, via O_DIRECT,
and I am working on something similar to posix_fadvise to provide even more granular file
access controls, as well. 

[1] https://github.com/xedin/windmill
[2] https://0xax.gitbooks.io/linux-insides/content/DataStructures/radix-tree.html

> In process (uncompressed) page cache
> ------------------------------------
>
>                 Key: CASSANDRA-5863
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5863
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: T Jake Luciani
>            Assignee: Branimir Lambov
>              Labels: performance
>             Fix For: 3.x
>
>
> Currently, for every read, the CRAR reads each compressed chunk into a byte[], sends
it to ICompressor, gets back another byte[] and verifies a checksum.  
> This process is where the majority of time is spent in a read request.  
> Before compression, we would have zero-copy of data and could respond directly from the
page-cache.
> It would be useful to have some kind of Chunk cache that could speed up this process
for hot data, possibly off heap.



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