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Date: Tue, 11 Dec 2012 15:01:25 +0000 (UTC)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12618595.1354554558181.18035.1355238085790@arcas>
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Subject: [jira] [Commented] (CASSANDRA-5020) Time to switch back to byte[]
 internally?
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    [ https://issues.apache.org/jira/browse/CASSANDRA-5020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529026#comment-13529026 ] 

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

using madvise/mincore is race prone (we purge it from cache on compaction, a read in progress pulls some back into cache, now we wait indefinitely for it to get pushed out of cache by other data).

using weakreferences means we're back to pre-1.0 of waiting for JVM GC before we can delete obsolete sstables.
                
> 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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