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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2252) off-heap memtables
Date Thu, 11 Aug 2011 04:35:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13082909#comment-13082909
] 

Jonathan Ellis commented on CASSANDRA-2252:
-------------------------------------------

bq. Adding region recycling post-flush

Of course this has the same reference counting problem as JNA free does: we can't re-use the
buffer until we're sure nobody's reading from it anymore.

I'm inclined to just do in-heap buffers for the memtables to start with.  Unlike cached rows,
we're virtually guaranteed contention on the memtable objects if we try to do AtomicInteger-based
reference counting, and sharded threadlocal counting is more of a pita than I want to tackle
at the moment.

I suspect that, like HBase, we'll realize substantial wins from area allocation even on-heap.

> off-heap memtables
> ------------------
>
>                 Key: CASSANDRA-2252
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2252
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Jonathan Ellis
>             Fix For: 1.0
>
>         Attachments: 0001-add-MemtableAllocator.txt, 0002-add-off-heap-MemtableAllocator-support.txt,
2252-v3.txt, merged-2252.tgz
>
>   Original Estimate: 0.4h
>  Remaining Estimate: 0.4h
>
> The memtable design practically actively fights Java's GC design.  Todd Lipcon gave a
good explanation over on HBASE-3455.

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