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

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.

Quick prototype seems like it will deliver quite quickly. I couldn't
see a reason to use "LET" rather than just "SET" which would be the
POLA choice.

Thoughts?

-- 
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services