Re: Offline enabling/disabling of data checksums

Hi,

Am Donnerstag, den 14.03.2019, 15:32 +0100 schrieb Magnus Hagander:
> On Thu, Mar 14, 2019 at 3:28 PM Christoph Berg <myon(at)debian(dot)org> wrote:
> > Re: Magnus Hagander 2019-03-14 <CABUevEx7QZLOjWDvwTdm1VM+mjsDm7=ZmB8qck7nDmcHEY5O5g(at)mail(dot)gmail(dot)com>
> > > Are you suggesting we should support running with a master with checksums
> > > on and a standby with checksums off in the same cluster? That seems.. Very
> > > fragile.
> >
> > The case "shut down master and standby, run pg_checksums on both, and
> > start them again" should be supported. That seems safe to do, and a
> > real-world use case.
>
> I can agree with that, if we can declare it safe. You might need some
> way to ensure it was shut down cleanly on both sides, I'm guessing. 
>
> > Changing the system id to a random number would complicate this.
> >
> > (Horrible idea: maybe just adding 1 (= checksum version) to the system
> > id would work?)
>
> Or any other way of changing the systemid in a predictable way would
> also work, right? As long as it's done the same on both sides. And
> that way it would look different to any system that *doesn't* know
> what it means, which is probably a good thing.

If we change the system identifier, we'll have to reset the WAL as well
or otherwise we'll get "PANIC:  could not locate a valid checkpoint
record" on startup. So even if we do it predictably on both primary and
standby I guess the standby would need to be re-cloned?

So I think an option that skips that for people who know what they are
doing with the streaming replication setup would be required, should we
decide to bump the system identifier.

Michael

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