Comment 11 for bug 742916

bah, wrong explain in my prior comment - here is the right one:

explain analyze SELECT max(branchrevision.sequence) as revno
  FROM Revision JOIN BranchRevision ON BranchRevision.revision = Revision.id
  WHERE BranchRevision.branch = 492361 AND branchrevision.sequence is not null and Revision.revision_date < '2009-08-10 21:56:30.623339+00:00';
                                                                                  QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate (cost=61101.68..61101.69 rows=1 width=4) (actual time=197.653..197.654 rows=1 loops=1)
   -> Nested Loop (cost=0.00..61091.07 rows=4245 width=4) (actual time=0.068..194.178 rows=9084 loops=1)
         -> Index Scan using revisionnumber_branch_sequence_unique on branchrevision (cost=0.00..29518.34 rows=4245 width=8) (actual time=0.043..70.559 rows=13262 loops=1)
               Index Cond: (branch = 492361)
               Filter: (sequence IS NOT NULL)
         -> Index Scan using changeset_pkey on revision (cost=0.00..7.43 rows=1 width=4) (actual time=0.008..0.008 rows=1 loops=13262)
               Index Cond: (revision.id = branchrevision.revision)
               Filter: (revision.revision_date < '2009-08-10 21:56:30.623339'::timestamp without time zone)
 Total runtime: 197.746 ms

This is half the estimated cost, which is an improvement - and 20% of the measured hot cost, which suggests quite some scattered data.