Re: Progress reporting for pg_verify_checksums

From: Fabien COELHO <fabien(dot)coelho(at)mines-paristech(dot)fr>
To: Michael Banck <michael(dot)banck(at)credativ(dot)de>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Bernd Helmle <mailings(at)oopsware(dot)de>, Michael Paquier <michael(at)paquier(dot)xyz>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Progress reporting for pg_verify_checksums
Date: 2019-02-19 15:37:30
Message-ID: alpine.DEB.2.21.1902191618580.7308@lancre
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Hallo Michael,

> New patch attached.

Patch applies cleanly. Compiles, "make check" ok. doc build is also ok.

There are no tests, which is probably fine for such an interactive

Docs look okay to me. Clear and to the point.

About :

total_percent = total_size ? (int64) ((current_size / MEGABYTES) * 100 / (total_size / MEGABYTES)) : 0;

MEGABYTES can be simplified and will enhance precision. ISTM that the
percent could be a double:

total_percent = total_size ? 100.0 * current_size / total_size : 0.0 ;

and then just let fprintf do the rounding.

I would bother rounding down < 100% to 100, because then you would get

1560/1492 MB (100\%, X MB/s)

which is kind of silly. If it goes over it just mean that the initial
estimate was wrong, which might happen if the db is running (other patch
in the queue). I'm fine with over 100 if it is consistent with the MB
ratio next to it.

fprintf could be called once instead of twice by merging the eol and the
previous message.

Maybe I'd consider inverting the sizeonly boolean so that more is done
when true.

I'd still would use more precise than one second precision time so that
the speed displayed at the beginning is more realistic. eg I got on a
short test with probably in system cache files:

188/188 MB (100%, 188 MB/s)

but the reality is that it took 0.126 seconds, and the speed was really
1492 MB/s.


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