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From "Kristofer Karlsson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4740) Weak references cause extreme GC churn
Date Thu, 31 Jan 2013 16:03:12 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13567744#comment-13567744
] 

Kristofer Karlsson commented on LUCENE-4740:
--------------------------------------------

This seems to be somewhat addressed in trunk, with the inputs in http://svn.apache.org/repos/asf/lucene/dev/trunk/lucene/core/src/java/org/apache/lucene/store/ByteBufferIndexInput.java
removing themselves from the clones list on close(). Should that be backported to 3.x?
                
> 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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