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https://issues.apache.org/jira/browse/LUCENE-1600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699864#action_12699864
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Patrick Eger commented on LUCENE-1600:
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Hashmaps would work also, but then they either need to be synchronized or kept
per-thread, the former would probably kill all your performance gains and the
latter would be annoying i think. A moderate usage of String.intern() is fine i
think, my patch just takes it out of the hot-path (for my use-case at least).
Other uses of String.intern() in the codebase may have different
solutions/tradeoffs certainly.
> Reduce usage of String.intern(), performance is terrible
> --------------------------------------------------------
>
> Key: LUCENE-1600
> URL: https://issues.apache.org/jira/browse/LUCENE-1600
> Project: Lucene - Java
> Issue Type: Improvement
> Affects Versions: 2.4, 2.4.1
> Environment: Windows Server 2003 x64
> Hotspot JDK 1.6.0_12 64-bit
> Reporter: Patrick Eger
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 2.9
>
> Attachments: intern.png, intern_perf.patch
>
>
> I profiled a simple MatchAllDocsQuery() against ~1.5 million documents (8
> fields of short text, Field.Store.YES,Field.Index.NOT_ANALYZED_NO_NORMS),
> then retrieved all documents via searcher.doc(i, fs). String.intern() showed
> up as a top hotspot (see attached screenshot), so i implemented a small
> optimization to not intern() for every new Field(), instead forcing the
> intern in the FieldInfos class and adding a optional "internName" constructor
> to Field. This reduced execution time for searching and iterating through all
> documents by 35%. Results were similar for -server and -client.
> TRUNK (2.9) w/out patch: matched 1435563 in 8884 ms/search
> TRUNK (2.9) w/patch: matched 1435563 in 5786 ms/search
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