Re: Using pg_upgrade to change from 32 to 64 bit.

Bruce Momjian <bruce(at)momjian(dot)us> writes:
> On Thu, Mar 11, 2021 at 10:34:42AM +0000, Paul Smith wrote:
>> Just "for kicks" I decided to try to use pg_upgrade to do it (on a test
>> database).  The documentation seems to suggest that it won't work
>> "pg_upgrade does its best to make sure the old and new clusters are
>> binary-compatible, e.g., by checking for compatible compile-time settings,
>> *including 32/64-bit binaries*."
>> To my surprise, it seemed to work absolutely fine. I can start the new 64 bit
>> cluster, and a quick check shows everything working OK.

Yeah, it will (probably) work as long as maxAlign is the same.
Since on Intel hardware that's pretty nearly a free choice by the
compiler, it doesn't surprise me if 32- and 64-bit Windows builds
use the same value.

> Well, pg_upgrade checks all the pg_controldata fields that would affect
> compatibility, so I guess it does work. pg_upgrade only really cares
> about the format of the database files, not the size of pointers used by
> the binary.

After some digging, I found where pg_upgrade checks that the clusters'
pg_control.maxAlign settings match. However, it looks to me like
pg_control.floatFormat is never checked, which is a problem in theory
though I'm not sure there's any issue in practice, seeing how universal
IEEE floats are. Perhaps more critical, it's not apparent to me where
or how pg_upgrade verifies that endianness is the same.

regards, tom lane