Re: [HACKERS] why not parallel seq scan for slow functions

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Marina Polyakova <m(dot)polyakova(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Subject: Re: [HACKERS] why not parallel seq scan for slow functions
Date: 2018-03-27 17:29:48
Message-ID: CA+TgmobAttbu5QeDc68juR_is9G5up-DD3Jh=V45ZxxJ7Q3njg@mail.gmail.com
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On Tue, Mar 27, 2018 at 7:42 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Mar 27, 2018 at 1:45 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> If we don't want to go with the upperrel logic, then maybe we should
>> consider just merging some of the other changes from my previous patch
>> in 0003* patch you have posted and then see if it gets rid of all the
>> cases where we are seeing a regression with this new approach.
>
> Which changes are you talking about?

I realized that this version could be optimized in the case where the
scanjoin_target and the topmost scan/join rel have the same
expressions in the target list. Here's a revised patch series that
does that. For me, this is faster than master on your last test case.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Attachment Content-Type Size
0004-Rewrite-the-code-that-applies-scan-join-targets-to-p.patch application/octet-stream 62.8 KB
0003-Postpone-generate_gather_paths-for-topmost-scan-join.patch application/octet-stream 6.1 KB
0002-CP_IGNORE_TLIST.patch application/octet-stream 6.5 KB
0001-Teach-create_projection_plan-to-omit-projection-wher.patch application/octet-stream 3.5 KB

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