[jira] [Created] (LUCENE-5721) Monotonic packed could maybe be faster

["Robert Muir (JIRA)" <ji...@apache.org>]

Robert Muir created LUCENE-5721:
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             Summary: Monotonic packed could maybe be faster
                 Key: LUCENE-5721
                 URL: https://issues.apache.org/jira/browse/LUCENE-5721
             Project: Lucene - Core
          Issue Type: Improvement
            Reporter: Robert Muir


This compression is used in lucene for monotonically increasing offsets, e.g. stored fields index, dv BINARY/SORTED_SET offsets, OrdinalMap (used for merging and faceting dv) and so on.

Today this stores a +/- deviation from an expected line of y=mx + b, where b is the minValue for the block and m is the average delta from the previous value. Because it can be negative, we have to do some additional work to zigzag-decode.

Can we just instead waste a bit for every value explicitly (lower the minValue by the min delta) so that deltas are always positive and we can have a simpler decode? Maybe If we do this, the new guy should assert that values are actually monotic at write-time. The current one supports "mostly monotic" but do we really need that flexibility anywhere? If so it could always be kept...



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