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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4740) Weak references cause extreme GC churn
Date Thu, 31 Jan 2013 16:09:22 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13567751#comment-13567751
] 

Uwe Schindler commented on LUCENE-4740:
---------------------------------------

bq. I replaced those maps with regular ConcurrentHashMap<Class, X> without any negative
impact.

This kills the possibility of unloading web applications in application servers. Those maps
don't produce many references.

Which OS are you using? Somebody had a similar problem on Windows.
                
> Weak references cause extreme GC churn
> --------------------------------------
>
>                 Key: LUCENE-4740
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4740
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/store
>    Affects Versions: 3.6.1
>         Environment: Linux debian squeeze 64 bit, Oracle JDK 6, 32 GB RAM, 16 cores
>            Reporter: Kristofer Karlsson
>            Priority: Critical
>
> We are running a set of independent search machines, running our custom software using
lucene as a search library. We recently upgraded from lucene 3.0.3 to 3.6.1 and noticed a
severe degradation of performance.
> After doing some heap dump digging, it turns out the process is stalling because it's
spending so much time in GC. We noticed about 212 million WeakReference, originating from
WeakIdentityMap, originating from MMapIndexInput.
> Our problem completely went away after removing the clones weakhashmap from MMapIndexInput,
and as a side-effect, disabling support for explictly unmapping the mmapped data.

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