Re: CTE inlining

On 04/05/2017 08:34, Petr Jelinek wrote:
> 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
>

+1 too

--
Julien Rouhaud
http://dalibo.com - http://dalibo.org