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Date: Mon, 25 Oct 2010 15:14:19 -0400 (EDT)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Subject: [jira] Created: (LUCENE-2723) Speed up Lucene's low level bulk
 postings read API
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Speed up Lucene's low level bulk postings read API
--------------------------------------------------

                 Key: LUCENE-2723
                 URL: https://issues.apache.org/jira/browse/LUCENE-2723
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Index
            Reporter: Michael McCandless
            Assignee: Michael McCandless
             Fix For: 4.0


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
http://chbits.blogspot.com/2010/08/lucene-performance-with-pfordelta-codec.html

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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