: That’s a very odd drop.  The only lucene commit that happened around
: then is LUCENE-8018, which really shouldn’t be making a difference to
: query performance.  And there’s no change to the PhraseQuery graphs.

Each run records the Git SHA it was run against -- the dip that's been
noted was beteen these 2 runs...

  Lucene/Solr trunk rev 81a4f7cc9cebf9c75387b1b498b556f6aa799932
  luceneutil rev 09a663e8054625f5173a92a21c9dd82c5a753dd7

  Lucene/Solr trunk rev f1a6b68d75e58f464b2ed4ee3702a6c1b14511a0
  luceneutil rev 09a663e8054625f5173a92a21c9dd82c5a753dd7

(although to be honest, i really don't understand the "stats" listed on
those URLs -- the "QPS prev" vs the "QPS now" doen't seem to match the
graph plot data for the same two dates -- so perhaps there is a reporting
glitch in what's actaully been tested in each run?)
Assuming those SHAs are correct, there are 2 other candidate commits
besides LUCENE-8018 (see below)

I'm not very familiar with exactly what code is run by each of these
benchmarks, but is it possible the Similarity changes in LUCENE-7997 had
an impact?  IIUC some stats/calculations were changed from floats to
doubles ... could that change account for this?
hossman@tray:~/lucene/dev [master] $ git log 81a4f7cc9cebf9c75387b1b498b556f6aa799932..f1a6b68d75e58f464b2ed4ee3702a6c1b14511a0 lucene/
commit 401dda7e064b6f621cba405985143724d79620c4
Author: Adrien Grand <[EMAIL PROTECTED]>
Date:   Fri Oct 27 08:36:27 2017 +0200

    LUCENE-8018: FieldInfos retains garbage if non-sparse.

commit 7d9cf438730e9cb7e251d1d2f5c6e81eba456f5c
Author: Steve Rowe <[EMAIL PROTECTED]>
Date:   Thu Oct 26 17:12:26 2017 -0400

    Add 6.6.2 back compat test indexes.

commit 42717d5f4bbed46009f11a86f307541a19fd7fb5
Author: Robert Muir <[EMAIL PROTECTED]>
Date:   Tue Oct 24 22:48:04 2017 -0400

    LUCENE-7997: More sanity testing of similarities ---------------------------------------------------------------------