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Date: Thu, 2 Mar 2006 21:04:41 +0100 (CET)
From: "Mark Harwood (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-509) Performance optimization when
 retrieving a single field from a document
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    [ http://issues.apache.org/jira/browse/LUCENE-509?page=comments#action_12368590 ] 

Mark Harwood commented on LUCENE-509:
-------------------------------------

>It would be nice if one could get just a few fields in an efficient manner too. 

I'd like to see that too. I put some code together to do that some time ago:

http://marc.theaimsgroup.com/?l=lucene-user&m=108525376821114&w=2

> Performance optimization when retrieving a single field from a document
> -----------------------------------------------------------------------
>
>          Key: LUCENE-509
>          URL: http://issues.apache.org/jira/browse/LUCENE-509
>      Project: Lucene - Java
>         Type: Improvement
>   Components: Index
>     Versions: 1.9, 2.0
>     Reporter: Steven Tamm
>  Attachments: DocField.patch, DocField_2.patch
>
> If you just want to retrieve a single field from a Document, the only way to do it is to retrieve all the fields from the Document and then search it.  This patch is an optimization that allows you retrieve a specific field from a document without instantiating a lot of field and string objects.  This reduces our memory consumption on a per query basis by around around 20% when a lot of documents are returned.
> I've added a lot of comments saying you should only call it if you only ever need one field.  There's also a unit test.

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