> > 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.)
You put me on the right track with your conclusion that the estimates
were off the chart. The quick-and-dirty fix "DELETE FROM pg_statistic;"
solved this problem. This database now have to build up sane estimates
from scratch.
/ Eskil