Track FieldInfo per segment instead of per-IW-session
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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
Fix For: Realtime Branch, CSF branch, 4.0
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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