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Date: Sun, 11 Mar 2012 14:25:59 +0000 (UTC)
From: "Robert Muir (Commented) (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-3841) CloseableThreadLocal does not work
 well with Tomcat thread pooling
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    [ https://issues.apache.org/jira/browse/LUCENE-3841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13227055#comment-13227055 ] 

Robert Muir commented on LUCENE-3841:
-------------------------------------

{quote}
Separately: maybe SnowballAnalyzer is too heavy...? Does it have some static data that ought to be loaded once and shared across analyzers... but isn't today?
{quote}

I think the analyzers are going to be heavy.

If we start going down the path of trying to speed up their instantiation time, then I vote to remove reusable tokenstreams completely.

That is: i don't think we should suffer the 'worst of both worlds'. either we go thru all the effort to make things reusable, or we dont
and instead worry about instantiation time, etc.

                
> CloseableThreadLocal does not work well with Tomcat thread pooling
> ------------------------------------------------------------------
>
>                 Key: LUCENE-3841
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3841
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/other
>    Affects Versions: 3.5
>         Environment: Lucene/Tika/Snowball running in a Tomcat web application
>            Reporter: Matthew Bellew
>            Assignee: Michael McCandless
>             Fix For: 3.6, 4.0
>
>
> We tracked down a large memory leak (effectively a leak anyway) caused
> by how Analyzer users CloseableThreadLocal.
> CloseableThreadLocal.hardRefs holds references to Thread objects as
> keys.  The problem is that it only frees these references in the set()
> method, and SnowballAnalyzer will only call set() when it is used by a
> NEW thread.
> The problem scenario is as follows:
> The server experiences a spike in usage (say by robots or whatever)
> and many threads are created and referenced by
> CloseableThreadLocal.hardRefs.  The server quiesces and lets many of
> these threads expire normally.  Now we have a smaller, but adequate
> thread pool.  So CloseableThreadLocal.set() may not be called by
> SnowBallAnalyzer (via Analyzer) for a _long_ time.  The purge code is
> never called, and these threads along with their thread local storage
> (lucene related or not) is never cleaned up.
> I think calling the purge code in both get() and set() would have
> avoided this problem, but is potentially expensive.  Perhaps using 
> WeakHashMap instead of HashMap may also have helped.  WeakHashMap 
> purges on get() and set().  So this might be an efficient way to
> clean up threads in get(), while set() might do the more expensive
> Map.keySet() iteration.
> Our current work around is to not share SnowBallAnalyzer instances
> among HTTP searcher threads.  We open and close one on every request.
> Thanks,
> Matt

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