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Posted to dev@lucene.apache.org by "Ryan Ernst (JIRA)" <ji...@apache.org> on 2015/06/25 05:14:06 UTC
[jira] [Comment Edited] (LUCENE-6585) Make ConjunctionDISI flatten
sub ConjunctionDISI instances
[ https://issues.apache.org/jira/browse/LUCENE-6585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14600601#comment-14600601 ]
Ryan Ernst edited comment on LUCENE-6585 at 6/25/15 3:14 AM:
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Commit 1687413 from [~rjernst] in branch 'dev/branches/branch_5x'
[ https://svn.apache.org/r1687413 ]
LUCENE-6585: Flatten conjunctions and conjunction approximations into parent conjunctions (merged from r1687408, r1687412)
was (Author: jira-bot):
Commit 1687413 from [~rjernst] in branch 'dev/branches/branch_5x'
[ https://svn.apache.org/r1687413 ]
LUCENE-6585: Remove println from testing
> Make ConjunctionDISI flatten sub ConjunctionDISI instances
> ----------------------------------------------------------
>
> Key: LUCENE-6585
> URL: https://issues.apache.org/jira/browse/LUCENE-6585
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Attachments: LUCENE-6585.patch, LUCENE-6585.patch
>
>
> Today ConjunctionDISI wraps some sub (two-phase) iterators. I would like to improve it by flattening sub iterators when they implement ConjunctionDISI. In practice, this would make "+A +(+B +C)" be executed more like "+A +B +C" (only in terms of matching, scoring would not change).
> My motivation for this is that if we don't flatten and are unlucky, we can sometimes hit some worst cases. For instance consider the 3 following postings lists (sorted by increasing cost):
> A: 1, 1001, 2001, 3001, ...
> C: 0, 2, 4, 6, 8, 10, 12, 14, ...
> B: 1, 3, 5, 7, 9, 11, 13, 15, ...
> If we run "+A +B +C", then everything works fine, we use A as a lead, and advance B 1000 by 1000 to find the next match (if any).
> However if we run "+A +(+B +C)", then we would iterate B and C 2 by 2 over the entire doc ID space when trying to find the first match which occurs on or after A:1.
> This is an extreme example which is unlikely to happen in practice, but flattening would also help a bit on some more common cases. For instance imagine that A, B and C have respective costs of 100, 10 and 1000. If you search for "+A +(+B +C)", then we will use the most costly iterator (C) to confirm matches of B (the least costly iterator, used as a lead) while it would have been more efficient to confirm matches of B with A first, since A is less costly than C.
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