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From "Stu Hood (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3168) Arena allocation causes excessive flushing on small heaps
Date Fri, 09 Sep 2011 18:37:09 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13101451#comment-13101451
] 

Stu Hood commented on CASSANDRA-3168:
-------------------------------------

+1.

> Arena allocation causes excessive flushing on small heaps
> ---------------------------------------------------------
>
>                 Key: CASSANDRA-3168
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3168
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 1.0.0
>            Reporter: Jonathan Ellis
>            Assignee: Jonathan Ellis
>             Fix For: 1.0.0
>
>         Attachments: 0002-3168.txt, 3168.txt
>
>
> adding allocator.size() to Memtable.getLiveSize has two problems:
> 1) it double-counts allocated parts of regions
> 2) it makes the size of an empty memtable the size of a single region
> (2) is a particular problem because flushing a nearly-empty memtable will not actually
free up much memory -- we just trade one almost-empty region, for another.  In testing, I
even saw this happening to the low-traffic system tables like LocationInfo.

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