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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5020) Time to switch back to byte[] internally?
Date Wed, 26 Dec 2012 20:48:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13539683#comment-13539683
] 

Jonathan Ellis commented on CASSANDRA-5020:
-------------------------------------------

Totally forgot the main reason DirectByteBuffer doesn't matter -- compression is on by default,
so optimizing for uncompressed data via mmap is silly.
                
> Time to switch back to byte[] internally?
> -----------------------------------------
>
>                 Key: CASSANDRA-5020
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5020
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>             Fix For: 2.0
>
>
> We switched to ByteBuffer for column names and values back in 0.7, which gave us a short
term performance boost on mmap'd reads, but we gave that up when we switched to refcounted
sstables in 1.0.  (refcounting all the way up the read path would be too painful, so we copy
into an on-heap buffer when reading from an sstable, then release the reference.)
> A HeapByteBuffer wastes a lot of memory compared to a byte[] (5 more ints, a long, and
a boolean).
> The hard problem here is how to do the arena allocation we do on writes, which has been
very successful in reducing STW CMS from heap fragmentation.  ByteBuffer is a good fit there.

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