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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5863) Create a Decompressed Chunk Cache
Date Fri, 09 Aug 2013 15:07:48 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13734871#comment-13734871
] 

T Jake Luciani commented on CASSANDRA-5863:
-------------------------------------------

The Tricky part is tracking the "hotness" of these chunks.  It needs to track the number of
times the chunk was decompressed in the last X seconds.  If this breaks some threshold then
it would put it in the cache.  This would keep things like compaction from causing churn.
                
> Create a Decompressed Chunk Cache
> ---------------------------------
>
>                 Key: CASSANDRA-5863
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5863
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: T Jake Luciani
>
> 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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