Re: Backport "WITH ... AS MATERIALIZED" syntax to <12?

On Sat, Oct 19, 2019 at 05:01:04AM +0100, Andrew Gierth wrote:
> >>>>> "Michael" == Michael Paquier <michael@paquier.xyz> writes:
>  > On Fri, Oct 18, 2019 at 02:21:30PM +0100, Colin Watson wrote:
>  >> However, an alternative would be to backport the new syntax to some
>  >> earlier versions. "WITH ... AS MATERIALIZED" can easily just be
>  >> synonymous with "WITH ... AS" in versions prior to 12; there's no
>  >> need to support "NOT MATERIALIZED" since that's explicitly
>  >> requesting the new query-folding feature that only exists in 12.
>  >> Would something like the attached patch against REL_11_STABLE be
>  >> acceptable? I'd like to backpatch it at least as far as PostgreSQL
>  >> 10.
> 
>  Michael> I am afraid that new features don't gain a backpatch. This is
>  Michael> a project policy. Back-branches should just include bug fixes.
> 
> I do think an argument can be made for making an exception in this
> particular case. This wouldn't be backpatching a feature, just accepting
> and ignoring some of the new syntax to make upgrading easier.

Right, this is my position too.  I'm explicitly not asking for
backpatching of the CTE-inlining feature, just trying to cope with the
fact that we now have to spell some particular queries differently to
retain the performance characteristics we need for them.

I suppose an alternative would be to add a configuration option to 12
that allows disabling inlining of CTEs cluster-wide: we could then
upgrade to 12 with inlining disabled, add MATERIALIZED to the relevant
queries, and then re-enable inlining.  But I like that less because it
would end up leaving cruft around in PostgreSQL's configuration code
somewhat indefinitely for the sake of an edge case in upgrading to a
particular version.

-- 
Colin Watson                                    [cjwatson@canonical.com]