Re: Progress reporting for pg_verify_checksums

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Michael Banck <michael(dot)banck(at)credativ(dot)de>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, alvherre(at)2ndquadrant(dot)com, mailings(at)oopsware(dot)de, thomas(dot)munro(at)enterprisedb(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Progress reporting for pg_verify_checksums
Date: 2019-03-30 17:52:56
Message-ID: alpine.DEB.2.21.1903301845420.29753@lancre
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Bonjour Michaƫl,

> Getting to know the total size and the current size are the two
> important factors that matter when it comes to do progress reporting
> in my opinion. I have read the patch, and I am not really convinced
> by the need to show the progress report based on an interval of 250ms
> as we talk about an operation which could take dozens of minutes.

I do not think that it matters. I like to see things moving, and the
performance impact is null.

> So I have simplified the patch to only show a progress report every
> second. This also removes the include for the time-related APIs from
> portability/.

I do not think that it is a good idea, because Michael is thinking of
adding some throttling capability, which would be a very good thing, but
which will need something precise, so better use the precise stuff from
the start. Also, the per second stuff induces rounding effects at the
beginning.

> A second thing is that I don't think that the speed is much useful.

Hmmm. I like this information because I this is where I have expectations,
whereas I'm not sure whether 1234 seconds for 12.3 GB is good or bad, but
I know that 10 MB/s on my SSD is not very good.

> I would expect the speed to be steady, still there is a risk to show
> incorrect information if the speed of the operation is spiky or
> irregular leading to an incorrect estimation of the remaining time.

Hmmm. That is life, I'd say I'm used to it.

> In short, I would like to commit the first patch as attached, which is
> much more simple than what has been sent previously, still it provides
> the progress information which is useful.

I would prefer that you would keep the patch with the initial precision &
features for the reasons outlined above, but you are the committer and I'm
only a reviewer.

--
Fabien.

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