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https://issues.apache.org/jira/browse/LUCENE-2881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13000229#comment-13000229
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Michael McCandless commented on LUCENE-2881:
--------------------------------------------
This was an impressive change :) Not only did we shift FieldInfos under
SegmentInfo, we also fixed a given FieldInfos to allow for sparse mapping (ie,
it only contains certain field numbers). Various places previously assumed
this was a dense mapping.
I think even in the DWPT case we should try to assign consistent field numbers?
I'm already worried enough about the possible perf hit DWPT will put on normal
indexing and the NRT case, since it basically pushes merging out from RAM and
onto the "normal" more costly disk based merging. If we also suddenly risk
these merges not being bulk merges, that's even worse.
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?
> 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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