| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: why partition pruning doesn't work? |
| Date: | 2018-06-07 22:33:03 |
| Message-ID: | CAKJS1f9xHoMntARi1RhqwAVZ-E0qp5a5f+Tf_chH9Vr8xOWiAw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 8 June 2018 at 03:43, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Maybe there's something I'm missing here, but I sort of hoped that this
> patch would nuke all the special-case code for Params in this area.
> Why is there any need to distinguish them from other stable expressions?
>
> IOW, I was hoping for the code to end up simpler, not more complicated.
We need to know which Params exist in the Expr as if there are no
Params, or only external Params, then we can run-time prune during
startup of the executor. Otherwise, we must leave the pruning until
during execution.
I really don't want to say goodbye to that optimisation as it's a
significant win to save having to initialise the subnodes for all the
useless partitions for OLTP type queries.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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