Adrien Grand created LUCENE-10033:
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Summary: Encode doc values in smaller blocks of values, like
postings
Key: LUCENE-10033
URL: https://issues.apache.org/jira/browse/LUCENE-10033
Project: Lucene - Core
Issue Type: Improvement
Reporter: Adrien Grand
This is a follow-up to the discussion on this thread:
https://lists.apache.org/thread.html/r7b757074d5f02874ce3a295b0007dff486bc10d08fb0b5e5a4ba72c5%40%3Cdev.lucene.apache.org%3E.
Our current approach for doc values uses large blocks of 16k values where
values can be decompressed independently, using DirectWriter/DirectReader. This
is a bit inefficient in some cases, e.g. a single outlier can grow the number
of bits per value for the entire block, we can't easily use run-length
compression, etc. Plus, it encourages using a different sub-class for every
compression technique, which puts pressure on the JVM.
We'd like to move to an approach that would be more similar to postings with
smaller blocks (e.g. 128 values) whose values get all decompressed at once
(using SIMD instructions), with skip data within blocks in order to efficiently
skip to arbitrary doc IDs (or maybe still use jump tables as today's doc
values, and as discussed here for postings:
https://lists.apache.org/thread.html/r7c3cb7ab143fd4ecbc05c04064d10ef9fb50c5b4d6479b0f35732677%40%3Cdev.lucene.apache.org%3E).
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