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

From: Justin Pryzby <pryzby(at)telsasoft(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, 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 21:13:37
Message-ID: 20211221211337.GB17618@telsasoft.com
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On Tue, Dec 21, 2021 at 12:33:06AM -0500, Tom Lane wrote:
> So now we have a real mystery about what is happening on Lars'
> system. Those numbers can't be right.

I realized Lars said it was x86_64/Linux, but I'm hoping to hear back with more
details:

What OS version?
Is it a VM of some type ?
How did you install postgres? From a package or compiled from source?
grep -r HAVE_CLOCK_GETTIME /usr/pgsql-13/include
Send the exact command and output you used to run the query?
Why does your explain output have IO timing but not Buffers: hit/read ?

--
Justin

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