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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 16:54:30 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12701994#action_12701994
] 

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

You could fix this, if you put all these field into the state object, too (an abstract class
instead of interface containing these variables) and cloning those on creating the new state.
But then you have the mentioned problem, that one thread may exchange the state object to
a IndexRead, but another one still sees the reference to the IndexNotRead object, not used
any longer. As log as you not also sychronize the state object change or make it volatile
in Java 1.5 it will still not work. That was, what I meant.
In my opinion, this is not fixable in any case with these type of state objects, yes?

> 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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