Re: Poor query plan chosen in 9.0.3 vs 8.3.7

Brian Connolly <bconn(at)labkey(dot)com> writes:
> Any help that you can provide would be greatly appreciated.

I'd suggest trying to get rid of the weird little subselects, like this
one:

> ... SELECT * FROM assayresult."c69d129_particle_size_result_fields"
> WHERE (((SELECT Container FROM exp.Data WHERE RowId = DataId) IN
> ('d938da12-1b43-102d-a8a2-78911b79dd1c'))) ...

If you turned that into a regular join between
c69d129_particle_size_result_fields and Data, the planner probably
wouldn't be nearly as confused about how many rows would result.
It's the way-off rowcount estimate for this construct that's
causing most of the problem, AFAICS:

-> Seq Scan on c69d129_particle_size_result_fields (cost=0.00..229742.02 rows=348 width=59) (actual time=0.018..572.402 rows=69654 loops=1)
Filter: (((SubPlan 3))::text = 'd938da12-1b43-102d-a8a2-78911b79dd1c'::text)
SubPlan 3
-> Index Scan using pk_data on data (cost=0.00..3.27 rows=1 width=37) (actual time=0.004..0.005 rows=1 loops=69654)
Index Cond: (rowid = $2)

regards, tom lane