Re: CTE inlining

On 03/05/17 23:24, Merlin Moncure wrote:
> On Wed, May 3, 2017 at 12:33 PM, Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)com> 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 for option 1. This change will be welcome for a large number of
> queries, but forced materialization is a real need and I use it often.
> This comes off as a very reasonable compromise in my opinion unless it
> requires major coding gymnastics to implement.
>

+1 to this

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services