[ http://issues.apache.org/jira/browse/LUCENE-739?page=all ]
Michael Busch updated LUCENE-739:
---------------------------------
Attachment: mergeNorms.patch
> Performance improvement for SegmentMerger.mergeNorms()
> ------------------------------------------------------
>
> Key: LUCENE-739
> URL: http://issues.apache.org/jira/browse/LUCENE-739
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael Busch
> Assigned To: Michael Busch
> Priority: Minor
> Attachments: mergeNorms.patch
>
>
> This patch makes two improvements to SegmentMerger.mergeNorms():
> 1) When the SegmentMerger merges the norm values it allocates a new byte
> array to buffer the values for every field of every segment. The size of such
> an array equals the size of the corresponding segment, so if large segments
> are being merged, those arrays become very large, too.
> We can easily reduce the number of array allocations by reusing a byte array
> to buffer the norm values that only grows, if a segment is larger than the
> previous one.
> 2) Before a norm value is written it is checked if the corresponding document
> is deleted. If not, the norm is written using IndexOutput.writeByte(byte[]).
> This patch introduces an optimized case for segments that do not have any
> deleted docs. In this case the frequent call of IndexReader.isDeleted(int)
> can be avoided and the more efficient method IndexOutput.writeBytes(byte[],
> int) can be used.
> This patch only changes the method SegmentMerger.mergeNorms(). All unit tests
> pass.
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