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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-4740) Weak references cause extreme GC churn
Date Fri, 01 Feb 2013 11:23:13 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-4740?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Uwe Schindler updated LUCENE-4740:
----------------------------------

    Attachment: LUCENE-4740.patch

Better patch using the getter method instead stupid MMapDirectory.this.useUnmap.
                
> 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
>         Attachments: LUCENE-4740.patch, LUCENE-4740.patch
>
>
> 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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