Re: [UNVERIFIED SENDER] pg_upgrade can result in early wraparound on databases with high transaction load

> On 5 Jul 2022, at 18:59, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Given the lack of field complaints, it's probably not worth trying
> to do anything to restore that capability.  But we really ought to
> update pg_upgrade's code and docs in pre-v15 branches to say that
> the minimum supported source version is 9.0.

(reviving an old thread from the TODO)

Since we never got around to doing this we still refer to 8.4 as a possible
upgrade path in v14 and older.

There seems to be two alternatives here, either we bump the minimum version in
v14-v12 to 9.0 which is the technical limitation brought by 695b4a113ab, or we
follow the direction taken by e469f0aaf3c and set 9.2.  e469f0aaf3c raised the
minimum supported version to 9.2 based on the complexity of compiling anything
older using a modern toolchain.

It can be argued that making a change we don't cover with testing is unwise,
but we clearly don't test the current code either since it's broken.

The attached takes the conservative approach of raising the minimum supported
version to 9.0 while leaving the code to handle 8.4 in place.  While it can be
removed, the risk/reward tradeoff of gutting code in backbranches doesn't seem
appealing since the code will be unreachable with this check anyways.

Thoughts?

--
Daniel Gustafsson