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https://issues.apache.org/jira/browse/LUCENE-4740?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler updated LUCENE-4740:
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Attachment: LUCENE-4740.patch
Patch that makes the unmapping behaviour consistent. The "unmap" setting is now
maintained by each MMapIndexInput. The unmap method was also moved into the
impl class (the previous implementation was a relict from older times)
> 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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