Re: [HACKERS] CTE inlining

On 04/05/17 05:33, Alvaro Herrera wrote:
> David Fetter wrote:
>
>> When we add a "temporary" GUC, we're taking on a gigantic burden.
>> Either we support it forever somehow, or we put it on a deprecation
>> schedule immediately and expect to be answering questions about it for
>> years after it's been removed.
>>
>> -1 for the GUC.
> Absolutely.
>
> So ISTM we have three choices:
>
> 1) we switch unmarked CTEs as inlineable by default in pg11.  What seems
> likely to happen for a user that upgrades to pg11 is that 5 out of 10
> CTE-using queries are going to become faster than with pg10, and they
> are going to be happy; 4 out of five are going to see no difference, but
> they didn't have to do anything about it; and the remaining query is
> going to become slower, either indistinguishably so (in which case they
> don't care and they remain happy because of the other improvements) or
> notably so, in which case they can easily figure where to add the
> MATERIALIZED option and regain the original performance.
+1

I've watched a colleague spend hours trying to optimise a complicated 
query with nested views, then find that this 'optimisation fence' was 
the heart of the problem.


Cheers,
Gavin