Re: statistics target for columns in unique constraint?

On Mon, May 13, 2013 at 6:01 PM, ach <alanchines@gmail.com> wrote:
> what I'm wondering is, since
> the unique constraint already covers the whole table and all rows in
> entirety, is it really necessary for statistics to be set that high on
> those?

AFAIK if there are exact-matching unique constraints/indexes for a
query's WHERE clause, the planner will deduce that the query only
returns 1 row and won't consult statistics at all.

> Or does that only serve to slow down inserts to that table?

It doesn't slow down inserts directly. Tables are analyzed in the
background by autovacuum. However, I/O traffic from autovacuum analyze
may slow down inserts running concurrently.

Regards,
Marti