Re: More stable query plans via more predictable column statistics

On Fri, Mar 4, 2016 at 7:27 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Thu, Mar 3, 2016 at 2:48 AM, Shulgin, Oleksandr
> <oleksandr(dot)shulgin(at)zalando(dot)de> wrote:
> > On Wed, Mar 2, 2016 at 7:33 PM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com
> >
> > wrote:
> >> Shulgin, Oleksandr wrote:
> >>
> >> > Alright. I'm attaching the latest version of this patch split in two
> >> > parts: the first one is NULLs-related bugfix and the second is the
> >> > "improvement" part, which applies on top of the first one.
> >>
> >> So is this null-related bugfix supposed to be backpatched? (I assume
> >> it's not because it's very likely to change existing plans).
> >
> > For the good, because cardinality estimations will be more accurate in
> these
> > cases, so yes I would expect it to be back-patchable.
>
> -1. I think the cost of changing existing query plans in back
> branches is too high. The people who get a better plan never thank
> us, but the people who (by bad luck) get a worse plan always complain.
>

They might get that different plan when they upgrade to the latest major
version anyway. Is it set somewhere that minor version upgrades should
never affect the planner? I doubt so.

--
Alex