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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