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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1609) Eliminate synchronization contention on initial index reading in TermInfosReader ensureIndexIsRead
Date Thu, 23 Apr 2009 16:02:31 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12701973#action_12701973
] 

Uwe Schindler commented on LUCENE-1609:
---------------------------------------

Are you sure, this works correct? If the indexState is changed in the synchronized block,
another thread not synchronizing on the lock may still see the old indexState. At least, the
indexState must be volatile, but this only works correct with Java 1.5 (and Lucene only needs
Java 1.4 as requirement).

> Eliminate synchronization contention on initial index reading in TermInfosReader ensureIndexIsRead

> ---------------------------------------------------------------------------------------------------
>
>                 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
>         Attachments: LUCENE-1609.patch
>
>
> 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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