Alexander Okulovich <aokulovich@stiltsoft.com> writes:
> We used the product with the default settings. The requests are simple.
> We didn't change the hardware (actually, we use even more performant
> hardware because of that issue) and DDL. I've checked the request on old
> and new databases. Requests that rely on this index execute more than 10
> times longer. Planner indeed used Index Scan before, but now it doesn't.
> So, from my perspective, the only reason we experience that is database
> logic change.
[ shrug... ] Maybe, but it's still not clear if it's a bug, or an
intentional change, or just a cost estimate that was on the hairy
edge before and your luck ran out.
If you could provide a self-contained test case that performs 10x worse
under v15 than v12, we'd surely take a look at it. But with the
information you've given so far, little is possible beyond speculation.
regards, tom lane