Re: Offline enabling/disabling of data checksums

On 2019-03-19 16:55:12 +0100, Michael Banck wrote:
> Hi,
> 
> Am Dienstag, den 19.03.2019, 08:36 -0700 schrieb Andres Freund:
> > On 2019-03-18 17:13:01 +0900, Michael Paquier wrote:
> > > +/*
> > > + * Locations of persistent and temporary control files.  The control
> > > + * file gets renamed into a temporary location when enabling checksums
> > > + * to prevent a parallel startup of Postgres.
> > > + */
> > > +#define CONTROL_FILE_PATH        "global/pg_control"
> > > +#define CONTROL_FILE_PATH_TEMP    CONTROL_FILE_PATH ".pg_checksums_in_progress"
> > 
> > I think this should be outright rejected. Again, you're making the
> > control file into something it isn't. And there's no buyin for this as
> > far as I can tell outside of Fabien and you. For crying out loud, if the
> > server crashes during this YOU'VE CORRUPTED THE CLUSTER.
> 
> The cluster is supposed to be offline during this.  This is just an
> additional precaution so that nobody starts it during the operation -
> similar to how pg_upgrade disables the old data directory.

I don't see how that matters. Afterwards the cluster needs low level
surgery to be recovered. That's a) undocumented b) likely to be done
wrongly.  This is completely unacceptable *AND UNNECESSARY*.

Greetings,

Andres Freund