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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2529) always apply position increment gap between values
Date Mon, 04 Oct 2010 16:19:32 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12917650#action_12917650
] 

Robert Muir commented on LUCENE-2529:
-------------------------------------

bq. but there is some other increment logic in this class that foils my attempts to coordinate
the positions across multiple fields, particularly when the first value is non-existent for
a multi-valued field.

I don't think this will ever completely work correctly though, for example the only way to
"accumulate" positions across a field that ends with a stopword / all stopwords would be to
add a positional equivalent to end() that we did for offsets, so that highlighting would work
for multi-valued fields. otherwise reset() -> clearAttributes() and the PositionIncrementAttribute
is "lost"

I think if you are trying to coordinate positions across multi-valued fields, it probably
means you shouldn't be using a multivalued field. It seems to only make sense to put multiple
*independent* values in a multi-valued field, not ones that are "continuations" of each other.
By definition if they are continuations of each other, I think its better to index the whole
thing as single-valued... and you have complete control of the positions within your tokenstream.


> 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_skip_posIncr_for_1st_token.patch, LUCENE-2529_skip_posIncr_for_1st_token.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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