Johan Fredriksson <eskil(at)kth(dot)se> writes:
> I am just about to upgrade from PostgreSQL 8.4.20 to 9.2.15, but I'v run
> into some huge performance issues.
The rowcount estimates from 9.2 seem greatly different from the 8.4 plan.
Did you remember to ANALYZE all the tables after migrating? Maybe there
were some table-specific statistics targets that you forgot to transfer
over? In any case, the 9.2 plan looks like garbage-in-garbage-out to
me :-( ... without estimates at least a little closer to reality, the
planner is unlikely to do anything very sane.
(BTW, I wonder why you are moving only to 9.2 and not something more
recent.)
regards, tom lane