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https://issues.apache.org/jira/browse/LUCENE-9850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17308225#comment-17308225
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Greg Miller commented on LUCENE-9850:
-------------------------------------
Just looking at the indexes produced by the luceneutil bench, it appears
there's ~0.3GB (2%) savings in index size by using PFOR over FOR for doc ID
deltas. So probably not worth the performance trade-off, unless I'm
misinterpreting the benchmark results:
{code:java}
> du -sk *
11653924
wikimediumall.baseline.facets.taxonomy:Date.taxonomy:Month.taxonomy:DayOfYear.sortedset:Month.sortedset:DayOfYear.Lucene90.Lucene90.nd33.3326M
11377548
wikimediumall.candidate.facets.taxonomy:Date.taxonomy:Month.taxonomy:DayOfYear.sortedset:Month.sortedset:DayOfYear.Lucene90.Lucene90.nd33.3326M
{code}
> Explore PFOR for Doc ID delta encoding (instead of FOR)
> -------------------------------------------------------
>
> Key: LUCENE-9850
> URL: https://issues.apache.org/jira/browse/LUCENE-9850
> Project: Lucene - Core
> Issue Type: Task
> Components: core/codecs
> Affects Versions: main (9.0)
> Reporter: Greg Miller
> Priority: Minor
>
> It'd be interesting to explore using PFOR instead of FOR for doc ID encoding.
> Right now PFOR is used for positions, frequencies and payloads, but FOR is
> used for doc ID deltas. From a recent
> [conversation|http://mail-archives.apache.org/mod_mbox/lucene-dev/202103.mbox/%3CCAPsWd%2BOp7d_GxNosB5r%3DQMPA-v0SteHWjXUmG3gwQot4gkubWw%40mail.gmail.com%3E]
> on the dev mailing list, it sounds like this decision was made based on the
> optimization possible when expanding the deltas.
> I'd be interesting in measuring the index size reduction possible with
> switching to PFOR compared to the performance reduction we might see by no
> longer being able to apply the deltas in as optimal a way.
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