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From "ASF subversion and git services (JIRA)" <>
Subject [jira] [Commented] (LUCENE-5721) Monotonic packed could maybe be faster
Date Thu, 05 Jun 2014 16:32:02 GMT


ASF subversion and git services commented on LUCENE-5721:

Commit 1600694 from [~jpountz] in branch 'dev/trunk'
[ ]

LUCENE-5721: Monotonic compression doesn't use zig-zag encoding anymore.

> Monotonic packed could maybe be faster
> --------------------------------------
>                 Key: LUCENE-5721
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Robert Muir
>            Assignee: Adrien Grand
>         Attachments: LUCENE-5703.patch
> 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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