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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-5863) Create a Decompressed Chunk Cache
Date Wed, 18 Sep 2013 01:07:52 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13734890#comment-13734890
] 

Jonathan Ellis edited comment on CASSANDRA-5863 at 9/18/13 1:06 AM:
--------------------------------------------------------------------

Probably easier to just special case seq scans to not cache, the way we did with fadvise pre-CASSANDRA-4937.
                
      was (Author: jbellis):
    Probably easier to just special case seq scans to not cache, the way we [used to?] do
with fadvise.
                  
> Create a Decompressed Chunk 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: Tyler Hobbs
>             Fix For: 2.1
>
>
> 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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