Re: pg_control is missing a field for LOBLKSIZE

On Wed, Jun 18, 2014 at 3:28 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Wed, Jun 18, 2014 at 2:55 PM, Tom Lane <tgl@sss.pgh.pa.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).

OK, I agree that checking that wouldn't hurt anything.

-- 
Robert Haas
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