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From "robert engels (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1195) Performance improvement for TermInfosReader
Date Thu, 11 Sep 2008 05:16:45 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630091#action_12630091
] 

robert engels commented on LUCENE-1195:
---------------------------------------

Also, SafeThreadLocal can be trivially changed to reduce the synchronization times, by using
a synchronized map - then only the access is sync'd.

Since a ThreadLocal in Lucene is primarily read (after initial creation), a 1.5 lock designed
for read often, write rarely would be best.



> Performance improvement for TermInfosReader
> -------------------------------------------
>
>                 Key: LUCENE-1195
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1195
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.4
>
>         Attachments: lucene-1195.patch, lucene-1195.patch, lucene-1195.patch, SafeThreadLocal.java
>
>
> Currently we have a bottleneck for multi-term queries: the dictionary lookup is being
done
> twice for each term. The first time in Similarity.idf(), where searcher.docFreq() is
called.
> The second time when the posting list is opened (TermDocs or TermPositions).
> The dictionary lookup is not cheap, that's why a significant performance improvement
is
> possible here if we avoid the second lookup. An easy way to do this is to add a small
LRU 
> cache to TermInfosReader. 
> I ran some performance experiments with an LRU cache size of 20, and an mid-size index
of
> 500,000 documents from wikipedia. Here are some test results:
> 50,000 AND queries with 3 terms each:
> old:                  152 secs
> new (with LRU cache): 112 secs (26% faster)
> 50,000 OR queries with 3 terms each:
> old:                  175 secs
> new (with LRU cache): 133 secs (24% faster)
> For bigger indexes this patch will probably have less impact, for smaller once more.
> I will attach a patch soon.

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