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Re: Explain buffers display units.

From: Greg Stark <stark(at)mit(dot)edu>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: "<pgsql-hackers(at)postgresql(dot)org>" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Explain buffers display units.
Date: 2010-02-15 14:55:43
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Mon, Feb 15, 2010 at 2:22 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> a) Changed the line description to "Total Buffer Usage" which at least
>> hints that it's something more akin to the "Total runtime" listed at
>> the bottom than the "actual time".
>> b) Used units of memory -- I formatted them with 3 significant digits
>> (unless the unit is bytes or kB where that would be silly). It's just
>> what looked best to my eye.
> I wasn't aware we had consensus on making this change, which I see you
> committed less than an hour after posting this.

Well there was a 30+ message thread almost a week ago where there
seemed to be some contention over the issue of whether the numbers
should be averages or totals. But were there was no dispute over the
idea of printing in memory units instead of blocks.

Given the controversy over whether to display averages or totals and
given the issues raised towards the end of the thread that there are
no comparable estimated values printed so there's no particular need
to average them I opted for the minimal change of just labelling it
"Total Buffer Usage". It didn't seem there was consensus to change it
to averages per loop or to change the whole plan output to display
totals. And I didn't see anyone argue that saying calling out that it
was a total was a bad idea.

We can always continue tweak the details of the format such as adding
spaces before the units to make it similar to the pg_size_pretty().
I'm not sure I like the idea of making it exactly equivalent because
pg_size_pretty() doesn't print any decimals so it's pretty imprecise
for smaller values.


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