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https://issues.apache.org/jira/browse/LUCENE-5215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13774471#comment-13774471
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Michael McCandless commented on LUCENE-5215:
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Hmm, could we remove SCR.fieldInfos entirely? And, pass it into ctor (passing
null if it's not "shared"), and also into .getNormValues (it's only
SegmentReader that calls this)?
{quote}
bq. it looks like we are now double-opening the CFS file
Correct. It's also called from IndexWriter, which opened CFS if needed,
therefore I thought it's not so critical.
{quote}
I'm less worried about IW, which does this once on open; apps "typically" open
an IW and use it for a long time, opening many NRT readers from it.
But I don't like adding this double-open to SR's open path (SR's are
"typically" opened more frequently than IWs), if we can help it.
I mean technically I guess it's an optimization to not double-open the CFS file
... so we could instead open a follow-on issue to try to fix it.
> Add support for FieldInfos generation
> -------------------------------------
>
> Key: LUCENE-5215
> URL: https://issues.apache.org/jira/browse/LUCENE-5215
> Project: Lucene - Core
> Issue Type: New Feature
> Components: core/index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Attachments: LUCENE-5215.patch, LUCENE-5215.patch, LUCENE-5215.patch,
> LUCENE-5215.patch, LUCENE-5215.patch
>
>
> In LUCENE-5189 we've identified few reasons to do that:
> # If you want to update docs' values of field 'foo', where 'foo' exists in
> the index, but not in a specific segment (sparse DV), we cannot allow that
> and have to throw a late UOE. If we could rewrite FieldInfos (with
> generation), this would be possible since we'd also write a new generation of
> FIS.
> # When we apply NDV updates, we call DVF.fieldsConsumer. Currently the
> consumer isn't allowed to change FI.attributes because we cannot modify the
> existing FIS. This is implicit however, and we silently ignore any modified
> attributes. FieldInfos.gen will allow that too.
> The idea is to add to SIPC fieldInfosGen, add to each FieldInfo a dvGen and
> add support for FIS generation in FieldInfosFormat, SegReader etc., like we
> now do for DocValues. I'll work on a patch.
> Also on LUCENE-5189, Rob raised a concern about SegmentInfo.attributes that
> have same limitation -- if a Codec modifies them, they are silently being
> ignored, since we don't gen the .si files. I think we can easily solve that
> by recording SI.attributes in SegmentInfos, so they are recorded per-commit.
> But I think it should be handled in a separate issue.
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