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Date: Thu, 6 Mar 2014 15:32:44 +0000 (UTC)
From: "Benedict (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12662653.1375981121295.15610.1394119964965@arcas>
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Subject: [jira] [Commented] (CASSANDRA-5863) Create a Decompressed Chunk
 [block] Cache
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    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13922650#comment-13922650 ] 

Benedict commented on CASSANDRA-5863:
-------------------------------------

bq. Moving hot compressed chunks onto an SSD makes a lot of sense, but think that maybe these are two different tickets? One to bring the page/buffer cache in process, and store it uncompressed, the other to track hot file regions and store them on a cache drive.

Just realised this is exactly what [~jbellis] already suggested.

I would quite like to have a crack at this for 3.0 using CASSANDRA-6694 as a basis, so that we can move the cache off-heap and retain zero copy behaviour.

> Create a Decompressed Chunk [block] Cache
> -----------------------------------------
>
>                 Key: CASSANDRA-5863
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5863
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: T Jake Luciani
>            Assignee: Pavel Yaskevich
>              Labels: performance
>             Fix For: 2.1 beta2
>
>
> 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. Initially this could be a off heap cache but it would be great to put these decompressed chunks onto a SSD so the hot data lives on a fast disk similar to https://github.com/facebook/flashcache.


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