Re: Online enabling of checksums

On 08/01/2018 10:40 AM, Michael Banck wrote:
> Hi,
>
> Am Dienstag, den 31.07.2018, 18:56 -0400 schrieb Alvaro Herrera:
>> The ability to get checksums enabled is a killer feature; the
>> ability to do it with no restart ... okay, it's better than
>> requiring a restart, but it's not *that* big a deal.
>
> Well, it's a downtime and service interruption from the client's POV,
> and arguably we should remove the 'online' from the patch subject
> then. You can activate checksums on an offline instance already via
> the pg_checksums extensions to pg_verify_checksums that Michael
> Paquier and I wrote independently; of course, that downtime will be
> linerarily longer the more data you have.
>

IMHO the main work still happens while the instance is running, so I
don't see why the restart would make it "not online".

But keeping or not keeping "online" is not the main dilemma faced by
this patch, I think. That is, if we drop "online" from the name I doubt
it'll make it any more acceptable for those objecting to having to
restart the cluster.

> If this was one week before feature freeze, I would agree with you
> that it makes sense to ship it with the restart requirement rather
> than not shipping it at all. But we're several commitfests away from
> v12, so making an effort to having this work without a downtime
> looks like a reasonable requirement to me.
>

Why would all those pieces had to be committed at once? Why not to
commit what we have now (with the restart) and then remove the
restriction in a later commit?

I understand the desire to be able to enable checksums without a
restart, but kinda agree with Alvaro regarding incremental development.

In a way, the question is how far can we reasonably push the patch
author(s) to implement stuff we consider desirable, but he/she/they
decided it's not worth the time investment at this point.

To me, it seems like an immensely useful feature even with the restart,
and I don't think the restart is a major burden for most systems (it can
be, if your system has no maintenance windows, or course).

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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