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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5661) Discard pooled readers for cold data
Date Tue, 09 Jul 2013 08:29:50 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13703051#comment-13703051
] 

Pavel Yaskevich commented on CASSANDRA-5661:
--------------------------------------------

I think this discussion already outgrown proportions of the original problem, I want to suggest
we try currently implemented queueing approach with expiry and maximum memory size cap as
fix for problem related to memory usage (with LCS in particular) without introducing any additional
complexity on getSegment (e.g. borrowing) at least for next 1.2 release. And in the meantime
I'm open for discussion of other ways of handling caching which could be borrowing and gradual
control over each instance in the queue, like proposed multiway pool, without adding any significant
overhead on such critical path as reading file segments.  
                
> Discard pooled readers for cold data
> ------------------------------------
>
>                 Key: CASSANDRA-5661
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5661
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 1.2.1
>            Reporter: Jonathan Ellis
>            Assignee: Pavel Yaskevich
>             Fix For: 1.2.7
>
>         Attachments: CASSANDRA-5661.patch, DominatorTree.png, Histogram.png
>
>
> Reader pooling was introduced in CASSANDRA-4942 but pooled RandomAccessReaders are never
cleaned up until the SSTableReader is closed.  So memory use is "the worst case simultaneous
RAR we had open for this file, forever."
> We should introduce a global limit on how much memory to use for RAR, and evict old ones.

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