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https://issues.apache.org/jira/browse/LUCENE-4658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13604671#comment-13604671
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Shai Erera commented on LUCENE-4658:
------------------------------------
bq. ExternalField maybe?
I think of ExternalField as something that resides outside the index, while
CustomField is part of the index. Therefore I prefer custom vs external, but
that's just naming.
First, this issue may not be used by facets at all. And I agree with Robert
that there's no point making two implementations for a custom data format.
Today we have the payloads and BDV as enablers to encode arbitrary data into a
byte[] (BDV is faster). I think that should be enough, as long as what you want
is a per-document custom data.
But if you want to encode per-segment global data (e.g. a taxonomy, a graph),
then BDV (or payload) are not the right API as they are per-document. Rather, I
think it will be good if we have this CustomDataFormat which is completely
opaque to Lucene, yet gives the app a lot of flexibility: CustomField passed on
Documents (at least in my scenarios these per-document datum comprise the
larger per-segment data structure) takes an Object, CustomDataFormat encodes
them however it needs, and is also responsible for merging across segments, IR
gives you a CustomData back. That's it. You app can then cast and work with
that data however it wants. We can have the getCustomData take a field, in case
you want to encode two such structures, but we don't need to at first.
If for some reason the app needs custom data per-document and cannot work with
neither payloads nor BDV, then it needs to have a CustomData type that exposes
per-document API. In either case, Lucene should not care what's in that data
except in the indexing chain (to call the right format's API) and during merge,
to invoke CustomDataFormat.merge().
I hope that's enough?
> Per-segment tracking of external/side-car data
> ----------------------------------------------
>
> Key: LUCENE-4658
> URL: https://issues.apache.org/jira/browse/LUCENE-4658
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Attachments: LUCENE-4658.patch, LUCENE-4658.patch
>
>
> Spinoff from David's idea on LUCENE-4258
> (https://issues.apache.org/jira/browse/LUCENE-4258?focusedCommentId=13534352&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13534352
> )
> I made a prototype patch that allows custom per-segment "side-car
> data". It adds an abstract ExternalSegmentData class. The idea is
> the app implements this, and IndexWriter will pass each Document
> through to it, and call on it to do flushing/merging. I added a
> setter to IndexWriterConfig to enable it, but I think this would
> really belong in Codec ...
> I haven't tackled the read-side yet, though this is already usable
> without that (ie, the app can just open its own files, read them,
> etc.).
> The random test case passes.
> I think for example this might make it easier for Solr/ElasticSearch
> to implement things like ExternalFileField.
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