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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-2722) Sep codec should store less in terms dict
Date Mon, 25 Oct 2010 09:51:21 GMT


Michael McCandless commented on LUCENE-2722:

Note that this is a change to the index format, but no core codecs actually use the [abstract]
sep codec yet (LUCENE-1410 will change that).

So I ran a simple perf test using MockSep, which naively writes each vInt separately:

||Query||QPS trunk||QPS patch||Pct diff||||
|"unit state"|7.74|7.78|{color:green}0.4%{color}|
|+unit +state|10.75|10.95|{color:green}1.9%{color}|
|unit state|11.99|12.36|{color:green}3.1%{color}|

It's a good speedup for the two fuzzy queries and also u*d...

> Sep codec should store less in terms dict
> -----------------------------------------
>                 Key: LUCENE-2722
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.0
>         Attachments: LUCENE-2722.patch
> I'm working on improving Lucene's performance with int block codecs
> (FOR/PFOR), but in early perf testing I found that these codecs cause
> a big perf hit to those MTQs that need to scan many terms but don't
> end up accepting many of those terms (eg fuzzy, wildcard, regexp).
> This is because sep codec stores much more in the terms dict, since
> each file is separate, ie seek points for each of doc, frq, pos, pyl,
> skp files.
> So I'd like to shift these seek points to instead be stored in the doc
> file, except for the doc seek point itself.  Since a given query will
> always need to seek to the doc file, this does not add an extra seek.
> But it saves tons of vInt decodes for the next/seke intensive MTQs...

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