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From "Michael Busch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2881) Track FieldInfo per segment instead of per-IW-session
Date Mon, 28 Feb 2011 18:04:36 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13000438#comment-13000438
] 

Michael Busch commented on LUCENE-2881:
---------------------------------------

bq. Can't we sync globally on the assignment of field name -> number (the global map lookup)?
 And FieldInfos per-DWPT would share the same global map.  Wouldn't that keep us consistent
in the DWPT case?


Yes.  The global map is already shared across DWPTs and the lookup is synchronized on the
global map.  I think if we change the logic to always pick the next available global number
we would increase the likelihood that fields get bulk-merged.

It can't be perfect though, because e.g. if you use addIndexes() to add an external segment
that has a different field number assignment.  That's why we definitely have to keep the code
that can fallback to  a different local number if it's not possible to use the global number
in a segment.  But I agree that we should optimize for the "normal" indexing case.  And it
seems like we all agree that field number gaps are fine.

> Track FieldInfo per segment instead of per-IW-session
> -----------------------------------------------------
>
>                 Key: LUCENE-2881
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2881
>             Project: Lucene - Java
>          Issue Type: Improvement
>    Affects Versions: Realtime Branch, CSF branch, 4.0
>            Reporter: Simon Willnauer
>            Assignee: Michael Busch
>             Fix For: Realtime Branch, CSF branch, 4.0
>
>         Attachments: lucene-2881.patch, lucene-2881.patch, lucene-2881.patch, lucene-2881.patch,
lucene-2881.patch
>
>
> Currently FieldInfo is tracked per IW session to guarantee consistent global field-naming
/ ordering. IW carries FI instances over from previous segments which also carries over field
properties like isIndexed etc. While having consistent field ordering per IW session appears
to be important due to bulk merging stored fields etc. carrying over other properties might
become problematic with Lucene's Codec support.  Codecs that rely on consistent properties
in FI will fail if FI properties are carried over.
> The DocValuesCodec (DocValuesBranch) for instance writes files per segment and field
(using the field id within the file name). Yet, if a segment has no DocValues indexed in a
particular segment but a previous segment in the same IW session had DocValues, FieldInfo#docValues
will be true  since those values are reused from previous segments. 
> We already work around this "limitation" in SegmentInfo with properties like hasVectors
or hasProx which is really something we should manage per Codec & Segment. Ideally FieldInfo
would be managed per Segment and Codec such that its properties are valid per segment. It
also seems to be necessary to bind FieldInfoS to SegmentInfo logically since its really just
per segment metadata.  

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