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From "Stu Hood (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-2252) off-heap memtables
Date Fri, 04 Mar 2011 02:52:36 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13002414#comment-13002414
] 

Stu Hood commented on CASSANDRA-2252:
-------------------------------------

I'd like to go ahead and merge these patches together onto jbellis's version. Things that
I will cherry pick from the alternate patch:
* A generic Allocator interface, rather than referring to Memtables. There are various other
places that we need to apply slabbing
* The additional counter tests we added
* Using the slab allocator's allocation count to determine throughput for memtables

----

The other realization we've had about slab allocation is that unless _all_ sources of fragmentation
are eliminated, slabbing actually causes promotion failures to happen earlier, since it is
harder to promote a slab into a fragmented oldgen. The other sources of fragmentation we suspect
are:
* IndexSummaries (easily slabbed)
* the key and row caches (row cache tackled in CASSANDRA-1969)

These can probably be defragged in separate tickets, as long as we commit to fixing them.

> 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: 0.8
>
>         Attachments: 0001-add-MemtableAllocator.txt, 0002-add-off-heap-MemtableAllocator-support.txt,
2252-alternate-v2.tgz
>
>
> The memtable design practically actively fights Java's GC design.  Todd Lipcon gave a
good explanation over on HBASE-3455.

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