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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nicolas Charles <nicolas.charles@normation.com>
Cc: pgsql-performance@lists.postgresql.org, Peter Geoghegan <pg@bowt.ie>
Cc: Shijia Wei <shijiawei@utexas.edu>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>
Subject: Re: Consecutive Query Executions with Increasing Execution Time
Date: Mon, 16 Dec 2019 17:48:16 -0500
Message-ID: <28107.1576536496@sss.pgh.pa.us> (raw)
In-Reply-To: <D0FEC9C2-0901-4C91-8641-6A5B8699C10C@normation.com>
References: <CABSfb-6iUvpGCzcgni+tVoiUWTc9aQdUtKbOzFzGqJcypiLa4g@mail.gmail.com>
	<adb87d39c5faa26d85274824ea4dd15ffc44ac40.camel@cybertec.at>
	<CABSfb-55VAcUwvy+PtsBsEk8EMfODtC6p65qVHSYhOqWWf80mA@mail.gmail.com>
	<CAH2-WzneCi_hM5_JGoPvGqKJr_Qd5hXcQzABz9-tQVndw9vwpw@mail.gmail.com>
	<19575.1576529417@sss.pgh.pa.us>
	<D0FEC9C2-0901-4C91-8641-6A5B8699C10C@normation.com>

Nicolas Charles <nicolas.charles@normation.com> writes:
> Could it be that your CPUs is warming and throttling? You didn't mention the platform used, so I'm not sure whether it's a server or a laptop

Hmm, that's an interesting thought.  The OP did say the CPU type,
but according to Intel's spec page for it [1] the difference between
base and turbo frequency is only 4.0 vs 4.2 GHz, which doesn't seem
like enough to explain the results ... unless you suppose it actually
throttled to below base freq, which surely shouldn't happen that fast.
Might be worth watching the CPU frequency while doing the test though.

I was speculating about some OS-level problem myself.  Plain old "top"
might be enough to show relevant info if it's in that area.

			regards, tom lane

[1] https://ark.intel.com/content/www/us/en/ark/products/88195/intel-core-i7-6700k-processor-8m-cache-up...





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