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Date: Sat, 25 Apr 2009 02:33:30 -0700 (PDT)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1612) expose lastDocId in the posting
 from the TermEnum API
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    [ https://issues.apache.org/jira/browse/LUCENE-1612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12702669#action_12702669 ] 

Michael McCandless commented on LUCENE-1612:
--------------------------------------------

This would be a good test (custom codec) for flexible indexing (LUCENE-1458), ie, allowing you to write whatever you want per-term.

Also, if lastDocID is always available, this could make merging of postings much faster than it is today, because you could bulk-copy the doc/freq posting bytes while just "fixing up" the boundary between them, because docIDs are delta coded.

> expose lastDocId in the posting from the TermEnum API
> -----------------------------------------------------
>
>                 Key: LUCENE-1612
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1612
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.4
>            Reporter: John Wang
>         Attachments: lucene-1612-patch.txt
>
>
> We currently have on the TermEnum api: docFreq() which gives the number docs in the posting.
> It would be good to also have the max docid in the posting. That information is useful when construction a custom DocIdSet, .e.g determine sparseness of the doc list to decide whether or not to use a BitSet.
> I have written a patch to do this, the problem with it is the TermInfosWriter encodes values in VInt/VLong, there is very little flexibility to add in lastDocId while making the index backward compatible. (If simple int is used for say, docFreq, a bit can be used to flag reading of a new piece of information)
> output.writeVInt(ti.docFreq);                       // write doc freq
>     output.writeVLong(ti.freqPointer - lastTi.freqPointer); // write pointers
>     output.writeVLong(ti.proxPointer - lastTi.proxPointer);
> Anyway, patch is attached with:TestSegmentTermEnum modified to test this. TestBackwardsCompatibility fails due to reasons described above.

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