Re: CTE inlining

On 5/3/17 9:54 PM, Andreas Karlsson wrote:
> On 05/03/2017 07:33 PM, Alvaro Herrera wrote:
>> 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.
>>
>>
>> 2) unmarked CTEs continue to be an optimization barrier, but we add
>> "WITH INLINED" so that they're inlineable. Some users may wonder about
>> it and waste a lot of time trying to figure out which CTEs to add it to.
>> They see a benefit in half the queries, which makes them happy, but they
>> are angry that they had to waste all that time on the other queries.
>>
>>
>> 3) We don't do anything, because we all agree that GUCs are not
>> suitable. No progress. No anger, but nobody is happy either.
>
> +1 for option 1. And while I would not like if we had to combine it with
> a backwards compatibility GUC which enables the old behavior to get it
> merged I still personally would prefer that over option 2 and 3.
>
> Andreas
>

+1 to what Andreas says

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