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Date: Thu, 30 Sep 2010 17:51:34 -0400 (EDT)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-2668) offset gap should be added
 regardless of existence of tokens in DocInverterPerField
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    [ https://issues.apache.org/jira/browse/LUCENE-2668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12916696#action_12916696 ] 

Michael McCandless commented on LUCENE-2668:
--------------------------------------------

bq. do you know why it conditionally decrements the position and then increments it later unconditionally? 

This was done in LUCENE-1542, to prevent position increment from becoming negative, which messes up positions if the field has a payload.  Basically we cannot store a -1 position if the field has a payload.

But I agree it's awful that we are inconsistent and it requires hacks for apps that have 0 posIncr on the first token.  Not sure how to best fix this though...

> offset gap should be added regardless of existence of tokens in DocInverterPerField
> -----------------------------------------------------------------------------------
>
>                 Key: LUCENE-2668
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2668
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>    Affects Versions: 2.9.3, 3.0.2, 3.1, 4.0
>            Reporter: Koji Sekiguchi
>            Assignee: Koji Sekiguchi
>            Priority: Minor
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2668.patch, LUCENE-2668.patch, LUCENE-2668.patch, Test.java
>
>
> Problem: If a multiValued field which contains a stop word (e.g. "will" in the following sample) only value is analyzed by StopAnalyzer when indexing, the offsets of the subsequent tokens are not correct.
> {code:title=indexing a multiValued field}
> doc.add( new Field( F, "Mike", Store.YES, Index.ANALYZED, TermVector.WITH_OFFSETS ) );
> doc.add( new Field( F, "will", Store.YES, Index.ANALYZED, TermVector.WITH_OFFSETS ) );
> doc.add( new Field( F, "use", Store.YES, Index.ANALYZED, TermVector.WITH_OFFSETS ) );
> doc.add( new Field( F, "Lucene", Store.YES, Index.ANALYZED, TermVector.WITH_OFFSETS ) );
> {code}
> In this program (soon to be attached), if you use WhitespaceAnalyzer, you'll get the offset(start,end) for "use" and "Lucene" will be use(10,13) and Lucene(14,20). But if you use StopAnalyzer, the offsets will be use(9,12) and lucene(13,19). When searching, since searcher cannot know what analyzer was used at indexing time, this problem causes out of alignment of FVH.
> Cause of the problem: StopAnalyzer filters out "will", anyToken flag set to false then offset gap is not added in DocInverterPerField:
> {code:title=DocInverterPerField.java}
> if (anyToken)
>   fieldState.offset += docState.analyzer.getOffsetGap(field);
> {code}
> I don't understand why the condition is there... If always the gap is added, I think things are simple.

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