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From: Justin Pryzby <pryzby@telsasoft.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David G. Johnston <david.g.johnston@gmail.com>
Cc: Lars Bergeson <larsavatar@gmail.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Query is slower with a large proportion of NULLs in several columns
Date: Tue, 21 Dec 2021 15:13:37 -0600
Message-ID: <20211221211337.GB17618@telsasoft.com> (raw)
In-Reply-To: <2707817.1640064786@sss.pgh.pa.us>
References: <CAK66RGYim22Sd8-NvmufcxEQ_P99=UTAyJ9agnwDyEbCiVGEQg@mail.gmail.com>
	<2688019.1640051519@sss.pgh.pa.us>
	<CAK66RGbd8n46xEp3fTKOa3pO3eC=NT8tEHHZYjuNZq4Y0SQHTw@mail.gmail.com>
	<20211221045138.GZ17618@telsasoft.com>
	<2704544.1640062888@sss.pgh.pa.us>
	<CAKFQuwZ==D+f656wsZcctpChQ2xWx5t2fjEhr8+VQWCSCWaWgQ@mail.gmail.com>
	<2707817.1640064786@sss.pgh.pa.us>

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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