Michael McCandless created LUCENE-6901:
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Summary: Optimize 1D dimensional value indexing
Key: LUCENE-6901
URL: https://issues.apache.org/jira/browse/LUCENE-6901
Project: Lucene - Core
Issue Type: Improvement
Reporter: Michael McCandless
Assignee: Michael McCandless
Fix For: Trunk
Dimensional values give a smaller index, and faster search times, for indexing
ordered byte[] values across one or more dimensions, vs our existing
approaches, but the indexing time is substantially slower.
Since the 1D case is so important/common (numeric fields, range query) I think
it's worth optimizing its indexing time. It should also be possible to
optimize the N > 1 dimensions case too, but it's more complex ... we can
postpone that.
So for the 1D case, I changed the merge method to do a merge sort (like
postings) of the already sorted segments dimensional values, instead of simply
re-indexing all values from the incoming segments, and this was a big speedup.
I also changed from {{InPlaceMergeSorter}} to {{IntroSorter}} (this is what
postings use, and it's faster but still safe) and this was another good
speedup, which should also help the > 1D cases.
Finally, I added a {{BKDReader.verify}} method (currently it's dark: NOT
called) that walks the index and then check that every value in each leaf block
does in fact fall within what the index expected/claimed. This is useful for
finding bugs! Maybe we can cleanly fold it into {{CheckIndex}} somehow later.
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