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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2881) Track FieldInfo per segment instead of per-IW-session
Date Wed, 02 Mar 2011 11:09:37 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13001372#comment-13001372
] 

Michael McCandless commented on LUCENE-2881:
--------------------------------------------

bq. I had the same thought while adding the ref to FieldInfos to SegmentInfo. Actually this
is probably the right thing to do. At the same time we could switch to a human-readable format


Human-readable format would be sweet :)

Though I'm still generally nervous that this means just opening the segments file will become
quite a bit more costly.  Apps that have many fields will be especially penalized, though,
apps really should not be creating so many fields.

bq. We could also store the global map on disk?

That's an interesting idea?  That'd ensure stability on the bindings, even for pre-4.0 indices.
 This way a pre-4.0 index would gradually work itself towards being fully consistent...

bq. addIndexes() would have to ignore the global map from the external index(es).

Well, addIndexes(IR[]) would get fully remapped to the correct bindings?  (since it's a real
merge).

But, yes, addIndexes(Dir[]) would not -- they are just file-copied.  Hmm, they'd also presumably
have a different global map, so if we stored the index global map in the Directory, how would
we resolve conflicts on the incoming addIndexes...?  I guess the local mapping for the incoming
segments would override the global one, on conflict.


> 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, 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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