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From "Dan Rosher (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-1609) Eliminate synchronization contention on initial index reading in TermInfosReader ensureIndexIsRead
Date Thu, 23 Apr 2009 15:28:30 GMT
Eliminate synchronization contention on initial index reading in TermInfosReader ensureIndexIsRead

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                 Key: LUCENE-1609
                 URL: https://issues.apache.org/jira/browse/LUCENE-1609
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Index
    Affects Versions: 2.9
         Environment: Solr 
Tomcat 5.5
Ubuntu 2.6.20-17-generic
Intel(R) Pentium(R) 4 CPU 2.80GHz, 2Gb RAM
            Reporter: Dan Rosher


synchronized method ensureIndexIsRead in TermInfosReader causes contention under heavy load

Simple to reproduce: e.g. Under Solr, with all caches turned off, do a simple range search
e.g. id:[0 TO 999999] on even a small index (in my case 28K docs) and under a load/stress
test application, and later, examining the Thread dump (kill -3) , many threads are blocked
on 'waiting for monitor entry' to this method.

Rather than using Double-Checked Locking which is known to have issues, this implementation
uses a state pattern, where only one thread can move the object from IndexNotRead state to
IndexRead, and in doing so alters the objects behavior, i.e. once the index is loaded, the
index nolonger needs a synchronized method. 

In my particular test, this uncreased throughput at least 30 times.



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