Re: Should we add GUCs to allow partition pruning to be disabled?

On Thu, Apr 19, 2018 at 2:54 AM, David Rowley
<david(dot)rowley(at)2ndquadrant(dot)com> wrote:
> If we just did it at plan time then
> pre-PREPAREd queries might still prune. That does not seem very
> useful if it's being disabled due to the discovery of some bug.
>

As you have pointed out upthread, that's a problem with every enable_*
GUC. After seeing a bug, users would usually re-prepare their
statements with pruning turned off. So, I don't see this as a reason
for introducing two GUCs.

> The more I think about this the more undecided I am as to whether we
> need to add a GUC for this at all, so I'm keen to hear more people
> voice their opinion about this. If bugs are the only true reason to
> add it, then the need for the GUC should diminish every day that
> nobody reports any bugs.
>

Apart from bugs, I think, this GUC can be used to avoid extra planning
time/memory/CPU incurred in pruning, when users know for sure that
pruning is not going to happen e.g. the cases like no qual on
partition key or no equality qual on hash partition key etc. Do we
know how much planning time can be saved this way?

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company