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https://issues.apache.org/jira/browse/LUCENE-2455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867951#action_12867951
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Shai Erera commented on LUCENE-2455:
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I've looked into implementing registerIndexes, and that's the approach I'd like
to take:
* For each incoming Directory, read its SegmentInfos
* For each SegmentInfo:
** Generate a new segment name
** List its files
** Copy them from incoming Dir to local Dir, w/ the new segment name
** Add such SI to the local IW segmentInfos
** Update DW docCount, like it's done in the addIndexes* methods.
Few things:
# Does that sound reasonable? Am I missing something?
# Directory exposes a copyTo(Dir, Collection) which I thought to use. But the
files are copied to the target Dir w/ their current name - while I need to copy
them over w/ their new name.
#* Adding rename to Dir feels wrong and dangerous to me
#* Adding copyFile(Dir, String old, String new) seems ok
#* Adding a variant of copyTo which accepts a Collection of the new names - the
src and new should align. This also seems ok to me.
I'd like to use Directory for the copy, since impls of Dir may do the copy very
efficiently (i.e. FSDir vs. RAMDir) and I don't want to use IndexInput/Output
for that.
Do you know of another way I can achieve that? I only want to copy the actual
segment files, w/o .gen and segments_N, so calling SI.files() seems ok?
Another question that popped into my head was about consistency of the incoming
Dirs vs. the local one, w.r.t. to CFS files - should I worry about that? I
think not because today one can create an index w/ CFS and then turn it off and
some segments will be compound and others not?
> 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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