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From "Ben Manes (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5661) Discard pooled readers for cold data
Date Sun, 07 Jul 2013 03:35:52 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13701495#comment-13701495
] 

Ben Manes commented on CASSANDRA-5661:
--------------------------------------

"rarely explicitly invalidated" is regards to a cache, as Jonathan originally described the
problem as a multimap cache instead of as an object pool. He also expressed concern with evicting
a block of buffers at once when he conceived of the same model that you implemented.

I am intimately familiar with Guava's cache as I designed the algorithms, ported and wrote
code for it, and advised on the api. Unfortunately I am not familiar with Cassandra's needs
and its code, so the pool was implemented based on a brief description of the problem and
ideal behavior.

It was a fun exercise for a long weekend. I'd recommend writing tests and benchmarks, which
unfortunately appears to be missing with the patch in its current form. Of couse use whatever
makes the most sense.
                
> 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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