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

From: Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: David Steele <david(at)pgmasters(dot)net>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>
Subject: Re: PoC plpgsql - possibility to force custom or generic plan
Date: 2017-03-19 13:30:28
Message-ID: 822e6132-6f6e-cc0b-c556-75649efeb7b2@2ndquadrant.com
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On 19/03/17 12:32, Pavel Stehule wrote:
>
>
> 2017-03-18 19:30 GMT+01:00 Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com
> <mailto:petr(dot)jelinek(at)2ndquadrant(dot)com>>:
>
> On 16/03/17 17:15, David Steele wrote:
> > On 2/1/17 3:59 PM, Pavel Stehule wrote:
> >> Hi
> >>
> >> 2017-01-24 21:33 GMT+01:00 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>
> >> <mailto:pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>>>:
> >>
> >> Perhaps that's as simple as renaming all the existing _ns_*
> >> functions to _block_ and then adding support for pragmas...
> >>
> >> Since you're adding cursor_options to PLpgSQL_expr it should
> >> probably be removed as an option to exec_*.
> >>
> >> I have to recheck it. Some cursor options going from dynamic
> >> cursor variables and are related to dynamic query - not query
> >> that creates query string.
> >>
> >> hmm .. so current state is better due using options like
> >> CURSOR_OPT_PARALLEL_OK
> >>
> >> if (expr->plan == NULL)
> >> exec_prepare_plan(estate, expr, (parallelOK ?
> >> CURSOR_OPT_PARALLEL_OK : 0) |
> >> expr->cursor_options);
> >>
> >> This options is not permanent feature of expression - and then I
> >> cannot to remove cursor_option argument from exec_*
> >>
> >> I did minor cleaning - remove cursor_options from plpgsql_var
> >>
> >> + basic doc
> >
> > This patch still applies cleanly and compiles at cccbdde.
> >
> > Any reviewers want to have a look?
> >
>
> I'll bite.
>
> I agree with Jim that it's not very nice to add yet another
> block/ns-like layer. I don't see why pragma could not be added to either
> PLpgSQL_stmt_block (yes pragma can be for whole function but function
> body is represented by PLpgSQL_stmt_block as well so no issue there), or
> to namespace code. In namespace since they are used for other thing
> there would be bit of unnecessary propagation but it's 8bytes per
> namespace, does not seem all that much.
>
> My preference would be to add it to PLpgSQL_stmt_block (unless we plan
> to add posibility to add pragmas for other loops and other things) but I
> am not sure if current block is easily (and in a fast way) accessible
> from all places where it's needed. Maybe the needed info could be pushed
> to estate from PLpgSQL_stmt_block during the execution.
>
>
> There is maybe partial misunderstand of pragma - it is set of nested
> configurations used in compile time only. It can be used in execution
> time too - it change nothing.
>
> The pragma doesn't build a persistent tree. It is stack of
> configurations that allows fast access to current configuration, and
> fast leaving of configuration when the change is out of scope.
>
> I don't see any any advantage to integrate pragma to ns or to
> stmt_block. But maybe I don't understand to your idea.
>
> I see a another possibility in code - nesting init_block_directives() to
> plpgsql_ns_push and free_block_directives() to plpgsql_ns_pop()
>

That's more or less what I mean by "integrating" to ns :)

The main idea is to not add 3rd layer of block push/pop that's sprinkled
in "random" places.

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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