Re: 7.4 - FK constraint performance

ow <oneway_111(at)yahoo(dot)com> writes:
> --- Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I think it must be using a seqscan for the foreign key check query.

> 2) prepare foo(my.dint) as
> SELECT 1 FROM ONLY "my"."large" x WHERE "small_id" = $1 FOR UPDATE OF x;

> explain analyze execute foo(201);

> QUERY PLAN
> Seq Scan on large x (cost=0.00..1787052.30 rows=7893843 width=6) (actual
> time=210566.301..210566.301 rows=0 loops=1)
> Filter: ((small_id)::integer = ($1)::integer)
> Total runtime: 210566.411 ms

Well, there's the smoking gun all right. Why does it think there are
going to be 7893843 matching rows!? Could we see the pg_stats row for
the large.small_id column?

regards, tom lane