[jira] [Commented] (CASSANDRA-5863) Create a Decompressed Chunk [block] Cache

["Pavel Yaskevich (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13889997#comment-13889997 ] 

Pavel Yaskevich commented on CASSANDRA-5863:
--------------------------------------------

Just to keep everybody updated, I didn't forget about this although got distracted by multiple things coming simultaneously, I tried multiple ways of using existing cache non of which yielded good performance. As Jake mentioned previously the hard part to track hotness of the sections + low cost lookup for already decompressed chunks, I have one more idea how to make it work, will keep you posted...

> 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
>
>
> 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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