Re: Query is slower with a large proportion of NULLs in several columns

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Cc: Lars Bergeson <larsavatar(at)gmail(dot)com>, pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: Query is slower with a large proportion of NULLs in several columns
Date: 2021-12-21 05:01:28
Message-ID: 2704544.1640062888@sss.pgh.pa.us
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Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> On Mon, Dec 20, 2021 at 08:11:42PM -0800, Lars Bergeson wrote:
>> Still taking 10X more I/O to read the smaller table. Very odd.

> If I'm not wrong, it's even worse than that ?
> It takes 20 or 30sec to run the query - but it says the associated I/O times
> are ~500sec or ~6000sec ?

It would help if somebody had labeled the units of I/O Time
... but I'm guessing those are microsec vs. the millisec
of the other times, because otherwise it's completely wrong.

regards, tom lane

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