Performance improvement for SegmentMerger.mergeNorms()
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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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