I wrote:
> The weird thing is that after a couple of hours of poking at it with
> oprofile and other sharp objects, I have no idea *why* it's slower.
> oprofile shows just about the same relative percentages for all the
> hot-spot functions in the backend.

However, some comparisons with gprof show that the planner is calling
the hot-spot functions more than it used to, which might be enough to
account for a couple percent on trivial queries like the ones being
issued by pg_bench ("SELECT abalance FROM accounts WHERE aid = :aid;").

After the holiday I'll look into refactoring to try to avoid the
extra calls.

Another issue is that on read-only transactions there's an extra
gettimeofday() call caused by pgstat_report_tabstats, which could be a
problem on machines with slow gettimeofday(). However that shouldn't
happen if you've got track_counts turned off, so if you don't see any
difference with or without stats then it's not the problem for you.

regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match