Re: Lengthy deletion

Herouth Maoz <herouth@unicell.co.il> writes:
> On 29/11/2011, at 09:13, Tom Lane wrote:
>> Yup, that's a clue all right.  I'll bet a nickel that you don't
>> have an index on the foreign key's referencing column (ie,
>> sent_messages.subscription_id).  That means each delete in
>> the referenced table has to seqscan the referencing table to
>> see if the delete would result in an FK violation.

> Makes sense. But shouldn't that be figured into the EXPLAIN plan?

If you run EXPLAIN ANALYZE, on a reasonably recent release, you'll see
the foreign-key trigger eating a lot of time.  Plain EXPLAIN doesn't
show triggers because it has no idea how much time they'll take.

            regards, tom lane