Re: why partition pruning doesn't work?

On Sat, Jun 2, 2018 at 5:16 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Fri, Jun 1, 2018 at 11:53 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>
>>
>> I agree though that it seems strange to special-case SQLValueFunction
>> rather than any-stable-expression. As long as the evaluation happens
>> at executor start (i.e. with the query's run-time snapshot) it should
>> be reasonable to simplify any stable expression.
>>
>> It's worth questioning whether this is a bug fix or an improvement.
>> If the latter, it probably ought to wait for v12.
>
>
> If explaining the change requires reference to tokens from the source code,
> rather than something an end user could understand, I'd argue it is a bug
> fix rather than an improvement.

If we going to implement stable expression folding before the actual
execution starts, that's a feature in itself. So, it's V12 material.
Partition pruning will use that feature. I don't think we should make
partition pruning work with stable expressions in some ad-hoc way in
V11 and the some future release (mostly V12) implements it on top of
stable expression folding feature. So my vote for making it work in
V12.

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