Mark Kirkwood <mark.kirkw...@catalyst.net.nz> writes: > I am in the progress of an 8.3 to 8.4 upgrade for a customer. I seem to > have stumbled upon what looks like a regression. The two databases > (8.3.14 and 8.4.8) have identical tuning parameters (where that makes > sense) and run on identical hardware. Both databases are regularly > vacuumed and analyzed (not by autovacuum), and performing an ANALYZE > does not change the plans shown below.
Hmmm ... this is structurally a pretty simple query, so I'm surprised that 8.3 and 8.4 see it very much differently. The relation-level estimates and plan choices are very nearly the same; the only thing that's changed much is the estimates of the join sizes, and there were not that many changes in the join selectivity estimation for simple inner joins. I wonder whether you are seeing a bad side-effect of this patch: http://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=7f3eba30 That code would only be reached when one or both join columns lack MCV lists in pg_stats; if you had analyzed, the only reason for that to be the case is if the column is unique (or nearly so, in ANALYZE's opinion). regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
