| From: | Noah Misch <noah(at)leadboat(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Jeff Davis <pgsql(at)j-davis(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Fabrízio Mello <fabriziomello(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Parallel Seq Scan |
| Date: | 2015-10-24 16:31:32 |
| Message-ID: | 20151024163132.GA436059@tornado.leadboat.com |
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| Lists: | pgsql-hackers |
On Sat, Oct 24, 2015 at 07:49:07AM -0400, Robert Haas wrote:
> On Fri, Oct 23, 2015 at 9:38 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> > Since that specification permits ParamListInfo consumers to ignore paramMask,
> > the plpgsql_param_fetch() change from copy-paramlistinfo-fixes.patch is still
> > formally required.
>
> So why am I not just doing that, then? Seems a lot more surgical.
do $$
declare
param_unused text := repeat('a', 100 * 1024 * 1024);
param_used oid := 403;
begin
perform count(*) from pg_am where oid = param_used;
end
$$;
I expect that if you were to inspect the EstimateParamListSpace() return
values when executing that, you would find that it serializes the irrelevant
100 MiB datum. No possible logic in plpgsql_param_fetch() could stop that
from happening, because copyParamList() and SerializeParamList() call the
paramFetch hook only for dynamic parameters. Cursors faced the same problem,
which is the raison d'être for setup_unshared_param_list().
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