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Posted to dev@lucene.apache.org by "Michael McCandless (JIRA)" <ji...@apache.org> on 2013/08/08 20:09:51 UTC
[jira] [Commented] (LUCENE-5159) compressed diskdv sorted/sortedset
termdictionaries
[ https://issues.apache.org/jira/browse/LUCENE-5159?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13733787#comment-13733787 ]
Michael McCandless commented on LUCENE-5159:
--------------------------------------------
+1, patch looks great.
> compressed diskdv sorted/sortedset termdictionaries
> ---------------------------------------------------
>
> Key: LUCENE-5159
> URL: https://issues.apache.org/jira/browse/LUCENE-5159
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Reporter: Robert Muir
> Attachments: LUCENE-5159.patch, LUCENE-5159.patch
>
>
> Sorted/SortedSet give you ordinal(s) per document, but them separately have a "term dictionary" of all the values.
> You can do a few operations on these:
> * ord -> term lookup (e.g. retrieving facet labels)
> * term -> ord lookup (reverse lookup: e.g. fieldcacherangefilter)
> * get a term enumerator (e.g. merging, ordinalmap construction)
> The current implementation for diskdv was the simplest thing that can possibly work: under the hood it just makes a binary DV for these (treating ordinals as document ids). When the terms are fixed length, you can address a term directly with multiplication. When they are variable length though, we have to store a packed ints structure in RAM.
> This variable length case is overkill and chews up a lot of RAM if you have many unique values. It also chews up a lot of disk since all the values are just concatenated (no sharing).
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