From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Thomas Munro <thomas.munro@gmail.com>, Stephen Frost <sfrost@snowman.net>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        David Steele <david@pgmasters.net>,
        Dmitry Dolgov <9erthalion6@gmail.com>,
        Jakub Wartak <Jakub.Wartak@tomtom.com>,
        Tomas Vondra <tomas.vondra@enterprisedb.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: WAL prefetch (another approach)
In-reply-to: <20210429001224.cdkef4ybkw7gramv@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Wed, 28 Apr 2021 17:12:24 -0700"
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Date: Wed, 28 Apr 2021 20:24:43 -0400
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Andres Freund <andres@anarazel.de> writes:
> On 2021-04-28 19:24:53 -0400, Tom Lane wrote:
>> IOW, we've spent over twice as many CPU cycles shipping data to the
>> standby as we did in applying the WAL on the standby.

> I don't really know how the time calculation works on mac. Is there a
> chance it includes time spent doing IO?

I'd be pretty astonished if it did.  This is basically a NetBSD system
remember (in fact, this ancient macOS release is a good deal closer
to those roots than modern versions).  BSDen have never accounted for
time that way AFAIK.  Also, the "ps" man page says specifically that
that column is CPU time.

> Oh! I was about to ask how much shared buffers your primary / standby
> have. And I think I may actually have reproduce a variant of the issue!

Default configurations, so 128MB each.

			regards, tom lane