Kristofer Karlsson created LUCENE-4740:
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Summary: 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/index
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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