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Date: Mon, 16 Nov 2009 23:27:39 +0000 (UTC)
From: "Jason Rutherglen (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-2075) Share the Term -> TermInfo cache
 across threads
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    [ https://issues.apache.org/jira/browse/LUCENE-2075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12778645#action_12778645 ] 

Jason Rutherglen commented on LUCENE-2075:
------------------------------------------

Solr used CHM as an LRU, however it turned out to be somewhat
less than truly LRU? I'd expect Google Collections to offer a
concurrent linked hash map however no dice?
http://code.google.com/p/google-collections/ 

Maybe there's a way to build a concurrent LRU using their CHM?

> Share the Term -> TermInfo cache across threads
> -----------------------------------------------
>
>                 Key: LUCENE-2075
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2075
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael McCandless
>            Priority: Minor
>             Fix For: 3.1
>
>
> Right now each thread creates its own (thread private) SimpleLRUCache,
> holding up to 1024 terms.
> This is rather wasteful, since if there are a high number of threads
> that come through Lucene, you're multiplying the RAM usage.  You're
> also cutting way back on likelihood of a cache hit (except the known
> multiple times we lookup a term within-query, which uses one thread).
> In NRT search we open new SegmentReaders (on tiny segments) often
> which each thread must then spend CPU/RAM creating & populating.
> Now that we are on 1.5 we can use java.util.concurrent.*, eg
> ConcurrentHashMap.  One simple approach could be a double-barrel LRU
> cache, using 2 maps (primary, secondary).  You check the cache by
> first checking primary; if that's a miss, you check secondary and if
> you get a hit you promote it to primary.  Once primary is full you
> clear secondary and swap them.
> Or... any other suggested approach?

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