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https://issues.apache.org/jira/browse/LUCENE-2455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12868191#action_12868191
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Shai Erera commented on LUCENE-2455:
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bq. any client apps that want to merge-in index data that does not correspond
1:1 to a Directory
I understand that. But when you call addIndexes w/ such IndexReaders, all they
do is read the postings. Those are written down using the logic of the target
IndexWriter. So I wonder how important is it for addIndexes to be in place,
rather than say rewriting those indexes before they are added? I mean, all that
addIndexes will do is call SegmentMerger and iterate on the readers and
segments, merging the posting lists ...
I don't object to that API. But, SM is used extensively, and is more of a
main-path code, while addIndexes(IndexReader) is something only few out there
use. Yet it affects everyone else who reads SM code, as well as those of us who
are confused about which method to call (Reader or Directory) ... It almost
feels like such operation - the relevant code from SM which handles
non-SegmentReaders, should be extracted to a utility or something. But if I'm
the only one that's bothered by it, then so be it. I can take care of the rest
now, and resolve that one later.
> Some house cleaning in addIndexes*
> ----------------------------------
>
> Key: LUCENE-2455
> URL: https://issues.apache.org/jira/browse/LUCENE-2455
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Priority: Trivial
> Fix For: 3.1, 4.0
>
> Attachments: LUCENE-2455_3x.patch
>
>
> Today, the use of addIndexes and addIndexesNoOptimize is confusing -
> especially on when to invoke each. Also, addIndexes calls optimize() in
> the beginning, but only on the target index. It also includes the
> following jdoc statement, which from how I understand the code, is
> wrong: _After this completes, the index is optimized._ -- optimize() is
> called in the beginning and not in the end.
> On the other hand, addIndexesNoOptimize does not call optimize(), and
> relies on the MergeScheduler and MergePolicy to handle the merges.
> After a short discussion about that on the list (Thanks Mike for the
> clarifications!) I understand that there are really two core differences
> between the two:
> * addIndexes supports IndexReader extensions
> * addIndexesNoOptimize performs better
> This issue proposes the following:
> # Clear up the documentation of each, spelling out the pros/cons of
> calling them clearly in the javadocs.
> # Rename addIndexesNoOptimize to addIndexes
> # Remove optimize() call from addIndexes(IndexReader...)
> # Document that clearly in both, w/ a recommendation to call optimize()
> before on any of the Directories/Indexes if it's a concern.
> That way, we maintain all the flexibility in the API -
> addIndexes(IndexReader...) allows for using IR extensions,
> addIndexes(Directory...) is considered more efficient, by allowing the
> merges to happen concurrently (depending on MS) and also factors in the
> MP. So unless you have an IR extension, addDirectories is really the one
> you should be using. And you have the freedom to call optimize() before
> each if you care about it, or don't if you don't care. Either way,
> incurring the cost of optimize() is entirely in the user's hands.
> BTW, addIndexes(IndexReader...) does not use neither the MergeScheduler
> nor MergePolicy, but rather call SegmentMerger directly. This might be
> another place for improvement. I'll look into it, and if it's not too
> complicated, I may cover it by this issue as well. If you have any hints
> that can give me a good head start on that, please don't be shy :).
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