[jira] [Commented] (CASSANDRA-5020) Time to switch back to byte[] internally?

["T Jake Luciani (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-5020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13509307#comment-13509307 ] 

T Jake Luciani commented on CASSANDRA-5020:
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It would seem the better fix is to do better ref counting.  There is a huge benefit to having the data mapped since it lives off heap.  

I've seen in mixed heavy read/write workloads this byte[] copy create a lot of heap pressure.
                
> 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: 1.3
>
>
> 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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