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

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

    [ https://issues.apache.org/jira/browse/LUCENE-5721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14014514#comment-14014514 ] 

Robert Muir commented on LUCENE-5721:
-------------------------------------

Also it would be nice to think about how much the floating point stuff saves compression-wise in practice. Maybe an integer average is enough?

> 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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