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From "Robert Muir (JIRA)" <>
Subject [jira] Commented: (LUCENE-2723) Speed up Lucene's low level bulk postings read API
Date Mon, 20 Dec 2010 22:09:01 GMT


Robert Muir commented on LUCENE-2723:

looks like the culprit to the slower low-freq terms (and the culprit to larger index) is this
in SepPostingsWriter:

      // nocommit -- only write if docFreq > skipInterval?

I think this hurts the low freq terms and why we see slow wildcards etc.

> Speed up Lucene's low level bulk postings read API
> --------------------------------------------------
>                 Key: LUCENE-2723
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.0
>         Attachments: LUCENE-2723-termscorer.patch, LUCENE-2723-termscorer.patch, LUCENE-2723-termscorer.patch,
LUCENE-2723.patch, LUCENE-2723.patch, LUCENE-2723.patch, LUCENE-2723.patch, LUCENE-2723.patch,
LUCENE-2723_bulkvint.patch, LUCENE-2723_facetPerSeg.patch, LUCENE-2723_facetPerSeg.patch,
LUCENE-2723_openEnum.patch, LUCENE-2723_termscorer.patch, LUCENE-2723_wastedint.patch
> Spinoff from LUCENE-1410.
> The flex DocsEnum has a simple bulk-read API that reads the next chunk
> of docs/freqs.  But it's a poor fit for intblock codecs like FOR/PFOR
> (from LUCENE-1410).  This is not unlike sucking coffee through those
> tiny plastic coffee stirrers they hand out airplanes that,
> surprisingly, also happen to function as a straw.
> As a result we see no perf gain from using FOR/PFOR.
> I had hacked up a fix for this, described at in my blog post at
> I'm opening this issue to get that work to a committable point.
> So... I've worked out a new bulk-read API to address performance
> bottleneck.  It has some big changes over the current bulk-read API:
>   * You can now also bulk-read positions (but not payloads), but, I
>      have yet to cutover positional queries.
>   * The buffer contains doc deltas, not absolute values, for docIDs
>     and positions (freqs are absolute).
>   * Deleted docs are not filtered out.
>   * The doc & freq buffers need not be "aligned".  For fixed intblock
>     codecs (FOR/PFOR) they will be, but for varint codecs (Simple9/16,
>     Group varint, etc.) they won't be.
> It's still a work in progress...

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