Re: BUG #17540: Prepared statement: PG switches to a generic query plan which is consistently much slower

On Thu, 7 Jul 2022 at 12:46, Andres Freund <andres@anarazel.de> wrote:
> I think the cost for the slow plan being so much cheaper can almost be
> qualified as bug.
>
> The slow plan seems pretty nonsensical to me. ISTM that something in the
> costing there is at least almost broken.

I forgot to mention what the "generic problem" is when I posted my
reply.  I should have mentioned that this is how we cost LIMIT. We
assume that we'll find the LIMIT 1 row after incurring the scan cost
multiplied by (1 / 259201).

For the plan with WHERE timestamp >= $1, the seqscan plan looks pretty
cheap for fetching DEFAULT_INEQ_SEL of the 259201 rows considering the
LIMIT multiples the cost of the scan by (1 / 86400).

David