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Date: Tue, 15 Apr 2014 18:03:15 +0000 (UTC)
From: "T Jake Luciani (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-5863) In process (uncompressed) page
 cache
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    [ https://issues.apache.org/jira/browse/CASSANDRA-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13969831#comment-13969831 ] 

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

I do think having a set of fast disks for hot data that doesn't fit into memory is key because in a large per node deployment you want:

1.  Memory (Really hot data)
2.  SSD (Hot data that doesn't fit in memory)
3.  Spinning disk (Historic cold data) 

[~benedict] you are describing building a custom page cache impl off heap which is pretty ambitious.  Don't you think a baby step would be to rely on the OS page cache to start and build a custom one as a phase II?

What would be the page size for uncompressed data.  For compressed the chunk size (conceptually) fits nicely. 

> In process (uncompressed) page 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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