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From "Michael Busch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1195) Performance improvement for TermInfosReader
Date Wed, 27 Feb 2008 01:04:53 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12572750#action_12572750
] 

Michael Busch commented on LUCENE-1195:
---------------------------------------

Test details:
The index has 500,000 docs and 3191625 unique terms. To construct the queries 
I used terms with 1000<df<3000, the index has 3880 of them. I combined the 
terms randomly. Each query has at least one hit. The AND queries have 25 hits 
on average, the OR queries 5641. 

The LRU cache was pretty small with a size of just 20.

The index is unoptimized with 11 segments.

> 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
>
>
> 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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