From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <david.rowley@2ndquadrant.com>
Cc: Jesper Pedersen <jesper.pedersen@redhat.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: converting Lists into arrays
Date: Fri, 9 Aug 2019 18:35:20 -0400
Message-ID: <20190809223520.GA28783@alvherre.pgsql> (raw)
In-Reply-To: <14960.1565384592@sss.pgh.pa.us>
On 2019-Aug-09, Tom Lane wrote:
> I poked at this, and attached is a patch, but again I'm not seeing
> that there's any real performance-based argument for it. So far
> as I can tell, if we've got a lot of RTEs in an executable plan,
> the bulk of the startup time is going into lock (re) acquisition in
> AcquirePlannerLocks, and/or permissions scanning in ExecCheckRTPerms;
> both of those have to do work for every RTE including ones that
> run-time pruning drops later on. ExecInitRangeTable just isn't on
> the radar.
I'm confused. I thought that the point of doing this wasn't that we
wanted to improve performance, but rather that we're now able to remove
the array without *losing* performance. I mean, those arrays were there
to improve performance for code that wanted fast access to specific list
items, but now we have fast access to the list items without it. So a
measurement that finds no performance difference is good news, and we
can get rid of the now-pointless optimization ...
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: alvherre@2ndquadrant.com, tgl@sss.pgh.pa.us, david.rowley@2ndquadrant.com, jesper.pedersen@redhat.com, andres@anarazel.de, robertmhaas@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: POC: converting Lists into arrays
In-Reply-To: <20190809223520.GA28783@alvherre.pgsql>
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