Re: PoC plpgsql - possibility to force custom or generic plan

On Fri, Sep 8, 2017 at 2:48 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>
>
> 2017-09-08 21:21 GMT+02:00 Daniel Gustafsson <daniel@yesql.se>:
>>
>> > On 08 Sep 2017, at 19:14, Simon Riggs <simon@2ndquadrant.com> wrote:
>> >
>> > On 6 September 2017 at 07:43, Robert Haas <robertmhaas@gmail.com> wrote:
>> >
>> >> LET custom_plan_tries = 0 IN SELECT ...
>> >
>> > Tom has pointed me at this proposal, since on another thread I asked
>> > for something very similar. (No need to reprise that discussion, but I
>> > wanted prepared queries to be able to do SET work_mem = X; SELECT).
>> > This idea looks a good way forward to me.
>> >
>> > Since we're all in roughly the same place, I'd like to propose that we
>> > proceed with the following syntax... whether or not this precisely
>> > solves OP's issue on this thread.
>> >
>> > 1. Allow SET to set multiple parameters...
>> > SET guc1 = x, guc2 = y
>> > This looks fairly straightforward
>> >
>> > 2. Allow a SET to apply only for a single statement
>> > SET guc1 = x, guc2 = y FOR stmt
>> > e.g. SET max_parallel_workers = 4 FOR SELECT count(*) FROM bigtable
>> > Internally a GUC setting already exists for a single use, via
>> > GUC_ACTION_SAVE, so we just need to invoke it.
>>
>> This syntax proposal makes sense, +1.  My immediate thought was that the
>> per-statement GUCs were sort of like options, and most options in our
>> syntax
>> are enclosed with (), like: SET (guc1 = x, guc2 = y) FOR SELECT ..;
>
> we newer support this syntax in combination with SET keyword
>
> see - CREATE FUNCTION command
>
> personally I prefer syntax without FOR keyword - because following keyword
> must be reserved keyword
>
> SET x = .., y = .. SELECT ... ;

This seems pretty ugly from a syntax perspective.

We already have 'SET LOCAL', which manages scope to the current
transaction.  How about SET BLOCK which would set until you've left
the current statement block?

merlin