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From "David Smiley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2529) always apply position increment gap between values
Date Tue, 05 Oct 2010 15:50:32 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12918034#action_12918034
] 

David Smiley commented on LUCENE-2529:
--------------------------------------

Quoting myself earlier:
bq. For multi-valued fields, it is now always the case that the first token of subsequent
values (e.g. not the first value) will be the previous position (0 if none) + the gap + the
first position increment of this value (typically 1). This is consistent and sensible. Formerly,
if the first value was a blank value (or a value consisting of stop words), then you'd get
1 less than what you get now. I hope the test I modified as part of this patch makes this
more clear; I had to increment the tested positions by 1.

> always apply position increment gap between values
> --------------------------------------------------
>
>                 Key: LUCENE-2529
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2529
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>    Affects Versions: 2.9.3, 3.0.2, 3.1, 4.0
>         Environment: (I don't know which version to say this affects since it's some
quasi trunk release and the new versioning scheme confuses me.)
>            Reporter: David Smiley
>            Assignee: Koji Sekiguchi
>            Priority: Minor
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2529_always_apply_position_increment_gap_between_values.patch,
LUCENE-2529_nonsenseIncrements.patch, LUCENE-2529_skip_posIncr_for_1st_token.patch, LUCENE-2529_skip_posIncr_for_1st_token.patch,
LUCENE-2529_skip_posIncr_for_1st_token.patch, LUCENE-2529_test.patch
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> I'm doing some fancy stuff with span queries that is very sensitive to term positions.
 I discovered that the position increment gap on indexing is only applied between values when
there are existing terms indexed for the document.  I suspect this logic wasn't deliberate,
it's just how its always been for no particular reason.  I think it should always apply the
gap between fields.  Reference DocInverterPerField.java line 82:
> if (fieldState.length > 0)
>           fieldState.position += docState.analyzer.getPositionIncrementGap(fieldInfo.name);
> This is checking fieldState.length.  I think the condition should simply be:  if (i >
0).
> I don't think this change will affect anyone at all but it will certainly help me.  Presently,
I can either change this line in Lucene, or I can put in a hack so that the first value for
the document is some dummy value which is wasteful.

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