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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-5020) Time to switch back to byte[] internally?
Date Tue, 11 Dec 2012 15:29:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529052#comment-13529052
] 

Jonathan Ellis edited comment on CASSANDRA-5020 at 12/11/12 3:28 PM:
---------------------------------------------------------------------

I don't think switching to byte[] is crazy either.  We'd save over 50% vs ByteBuffer on small
columns like ints, even if we are comparing off-heap-bytebuffer with on-heap-byte[], simply
because BB's extra fields are so big.

That is,

bq. A HeapByteBuffer wastes a lot of memory compared to a byte[] (5 more ints, a long, and
a boolean).

also goes for DirectByteBuffer (those fields are all declared in ByteBuffer that HBB and DBB
extend).
                
      was (Author: jbellis):
    I don't think switching to byte[] is crazy either.  We'd save over 50% vs ByteBuffer on
small columns like ints, even if we are comparing off-heap-bytebuffer with on-heap-byte[],
simply because BB's extra fields are so big.
                  
> 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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