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https://issues.apache.org/jira/browse/LUCENE-1600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699857#action_12699857
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Jason Rutherglen commented on LUCENE-1600:
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contrib/MemoryIndex has a bunch of notes about how interning is
slow, and using (I believe) hashmaps of strings is better.
Comments on this approach?

> 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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