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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6843) Reclaim overwritten off-heap memtable space early
Date Mon, 14 Apr 2014 13:11:16 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13968331#comment-13968331
] 

Benedict commented on CASSANDRA-6843:
-------------------------------------

So, in order to make this more palatable, I think it may be possible to make a dramatically
simpler patch based on CASSANDRA-6696 only, that simple delegates to unsafe.allocateMemory()
and unsafe.freeMemory(). A round of both clocks in at around 100-200ns, so in the grand scheme
of things isn't very hefty, but the code complexity here should be pretty minimal to zero.
We can have NativeAllocator configurably allocate from a block or simply the exact amount
requested, and if the latter we can buffer any free() requests up and periodically commit
any that were buffered prior to the latest OpOrder.Barrier issuance.

I would quite like to see this minor change make it into 2.1, as it should be really helpful
to those users with an overwrite workload. We can then kick the zero-copy and off-heap-gc
work down the road for now (i.e. abandon them for the time being).

[~xedin] [~slebresne] what do you think?

> Reclaim overwritten off-heap memtable space early
> -------------------------------------------------
>
>                 Key: CASSANDRA-6843
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6843
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>              Labels: performance
>             Fix For: 3.0
>
>
> Perform GC on the off-heap memtable arenas



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