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https://issues.apache.org/jira/browse/LUCENE-2881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12997252#comment-12997252
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Michael Busch commented on LUCENE-2881:
---------------------------------------

bq. I think we should initialize the codecID with a different value and replace 
the this.codecId != 0 check with something like this.codecId != -1.

Yeah, I had the same though.  I changed it to use -1 and use an assert now 
instead of throwing the exception.
(will post the new patch shortly)

bq. What exactly was the problem with the previous patch beside the codecID 
clone issue?

Not sure if that's what caused your codecID issues, but the previous patch had 
a problem with assigning field numbers.  It could happen that a global number 
for a FieldInfo was acquired, but that number wasn't available anymore in the 
local FieldInfos.  I think this would be quite rare, but now I'm preventing 
this from happening.

> 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
>
>
> 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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