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https://issues.apache.org/jira/browse/LUCENE-7371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15382404#comment-15382404
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Adrien Grand commented on LUCENE-7371:
--------------------------------------
The benchmarks are reporting interesting changes, some seem to perform slightly
faster now, like IntNRQ
(http://people.apache.org/~mikemccand/lucenebench/IntNRQ.html) or the geo3d
distance filter
(http://people.apache.org/~mikemccand/geobench.html#search-distance) but some
others seem to perform a bit slower like the 10-gon filter
(http://people.apache.org/~mikemccand/geobench.html#search-poly_10) or the 10
nearest points
(http://people.apache.org/~mikemccand/geobench.html#search-nearest_10). The
fact that it is not consistently slower or faster is due to the distribution of
points in the blocks that need to be read I think (the more unique leading
bytes, the more expensive the read). Given that the slow down is not general to
all benchmarks and that the size reduction is significant I don't think this
should be reverted, but let me know if you think otherwise. (For the record
many benchmarks look slower on July 17th but I don't think this is related to
this change, for instance even phrases got slower
http://people.apache.org/~mikemccand/lucenebench/Phrase.html)
> BKDReader could compress values better
> --------------------------------------
>
> Key: LUCENE-7371
> URL: https://issues.apache.org/jira/browse/LUCENE-7371
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: master (7.0), 6.2
>
> Attachments: LUCENE-7371.patch, LUCENE-7371.patch, LUCENE-7371.patch
>
>
> For compressing values, BKDReader only relies on shared prefixes in a block.
> We could probably easily do better. For instance there are only 256 possible
> values for the first byte of the dimension that the values are sorted by, yet
> we use a block size of 1024. So by using something simple like run-length
> compression we could save 6 bits per value on average.
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