[jira] [Created] (LUCENE-6901) Optimize 1D dimensional value indexing

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

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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