[jira] Commented: (LUCENE-2455) Some house cleaning in addIndexes*

["Michael McCandless (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-2455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866118#action_12866118 ] 

Michael McCandless commented on LUCENE-2455:
--------------------------------------------

bq. Remove optimize() call from addIndexes(IndexReader...)

This still makes me nervous.  Yeah it's bad that this method does optimize() now.  But if we remove it, it's bad that this method can attempt to do a ridiculously immense merge, since it [naively] just stuffs everything and and does one merge.  Ie, both at are bad.

Maybe... we could do this: only merge the the incoming IndexReaders, appending a new segment to the end of the index?  Ie do no merging whatsoever of the current segments in the index.

Yes, this can result in "unbalanced" segments (ie, a huge segment appears after the long tail of level 0 segments), but, the merge policy can handle this -- it'll work out whatever merges are then necessary to get this segment onto the level that roughly matches its size. 

bq. So unless you have an IR extension, addDirectories is really the one  you should be using.

You mean addIndexes(Directory..)?

{quote}
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 .
{quote}

This would be best of all :)  But it's tricky, because our MP/MS assume they are working w/ a SegmentInfo.  But, maybe it could somehow be made to work -- eg IR does give us maxDoc, numDocs (so we can know del doc count).  But eg LogByteSizeMergePolicy goes and computes total byte size of the segment (via SegmentInfo) which we cannot do from an IR.



> 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
>
>
> 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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