Re: pg_control is missing a field for LOBLKSIZE

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Jun 18, 2014 at 2:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The net behavior would be the same, but I thought it might be easier to
>> code by thinking of it this way. Or maybe it wouldn't --- it's just a
>> suggestion.

> Well, the difference is that if we just don't check it, there can
> never be an error. Basically, it's the user's job to DTRT. If we
> check it against some semi-arbitrary value, we'll catch the case where
> the old cluster was modified with a custom setting and the new one was
> not - but couldn't we also get false positives under obscure
> circumstances?

Huh? What we'd be checking is the LOBLKSIZE compiled into pg_upgrade
versus that stored into pg_control by the new postmaster. If those
are different, then pg_upgrade didn't come from the same build as the
new postmaster, which is already a pretty hazardous situation (especially
if the user is fooling with low-level stuff like this).

regards, tom lane