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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-2335) optimization: when sorting by field, if index has one segment and field values are not needed, do not load String[] into field cache
Date Fri, 19 Mar 2010 23:00:27 GMT
optimization: when sorting by field, if index has one segment and field values are not needed,
do not load String[] into field cache
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                 Key: LUCENE-2335
                 URL: https://issues.apache.org/jira/browse/LUCENE-2335
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Search
            Reporter: Michael McCandless
            Priority: Minor
             Fix For: 3.1


Spinoff from java-dev thread "Sorting with little memory: A suggestion", started by Toke Eskildsen.

When sorting by SortField.STRING we currently ask FieldCache for a StringIndex on that field.

This can consumes tons of RAM, when the values are mostly unique (eg a title field), as it
populates both int[] ords as well as String[] values.

But, if the index is only one segment, and the search sets fillFields=false, we don't need
the String[] values, just the int[] ords.  If the app needs to show the fields it can pull
them (for the 1 page) from stored fields.

This can be a potent optimization -- alot of RAM saved -- for optimized indexes.

When fixing this we must take care to share the int[] ords if some queries do fillFields=true
and some =false... ie, FieldCache will be called twice and it should share the int[] ords
across those invocations.

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