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https://issues.apache.org/jira/browse/CASSANDRA-5661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13693600#comment-13693600
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Jonathan Ellis commented on CASSANDRA-5661:
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It still looks like an LRU problem to me: I have room for N objects, when I try 
to allocate N+1 I throw away the LRU.

This means we will use more memory than a timer approach if N is actually more 
than we need, but it will do better than timers if we are crunched for space, 
which seems like the more important scenario to optimize.

It also means that we have a very clear upper bound on memory use, rather than 
depending on workload, which history shows is tough for users to tune.
                
> 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
>
>
> 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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