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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2529) always apply position increment gap between values
Date Fri, 09 Jul 2010 10:12:53 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12886670#action_12886670
] 

Michael McCandless commented on LUCENE-2529:
--------------------------------------------

I agree it's weird that the if checks fieldState.length instead of i; we should fix it, though,
this is a subtle break in back-compat.

Once we do LUCENE-2309 (fully decouple indexing & analysis) and LUCENE-2450 (write-once
attr bindings in the analyzer chain), this sort of fix would be nicely "external" to Lucene.
 Ie the semantics of how positions / offsets increment across boundaries of multiple fields
would be fully determined by the app/analyzer, not baked into Lucene's core.

> always apply position increment gap between values
> --------------------------------------------------
>
>                 Key: LUCENE-2529
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2529
>             Project: Lucene - Java
>          Issue Type: Improvement
>         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
>   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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