Re: [GENERAL] OUTER JOIN IS SLOW

Benjamin Arai <benjamin(at)araisoft(dot)com> writes:
> -> Index Scan using mutualfd_weekday_qbid_pkey_idx on
> mutualfd_weekday_qbid (cost=0.00..6.01 rows=1 width=19) (actual
> time=34.579..8510.801 rows=253 loops=1)
> Index Cond: ((pkey >= '2005-12-15'::date) AND (pkey <=
> '2006-12-15'::date))
> Filter: (cusip = '92193920'::text)

Hm, so how many rows in mutualfd_weekday_qbid for that date?
And how many satisfy the cusip condition? (I suppose 253,
but it looks like that must be a very small fraction of all
the rows for that date.)

The selectivity estimators are not great about dealing with
zero-width intervals like this one (in fact, if you look at the
code you'll find it doesn't even bother to distinguish '>' from '>='
... something we should probably try to improve sometime).

You'd probably have better luck if you could fold the WHERE condition
down to "pkey = '2005-12-15'". Dunno how feasible that is for your
application.

regards, tom lane