Re: Transactional sequence stuff breaks pg_upgrade

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> The problem is that if a relfilenode ever gets assigned by
> GetNewRelFileNode() during a binary-upgrade restore, that OID may turn
> out to be used by some other object later in the dump. And then
> you're dead, because the dump restore will fail later on complaining
> about, well, I forget the error message wording exactly, but,
> basically, an OID collision.

Right.

> So if we change the rules in such a way
> that objects which currently lack TOAST tables acquire them, we need
> to first restore all of the objects *without* adding any new TOAST
> tables, and then at the end create any new TOAST tables once we have a
> complete list of the relfilenodes that are actually used.

toasting.c explains why this currently doesn't seem necessary:

/*
* In binary-upgrade mode, create a TOAST table if and only if
* pg_upgrade told us to (ie, a TOAST table OID has been provided).
*
* This indicates that the old cluster had a TOAST table for the
* current table. We must create a TOAST table to receive the old
* TOAST file, even if the table seems not to need one.
*
* Contrariwise, if the old cluster did not have a TOAST table, we
* should be able to get along without one even if the new version's
* needs_toast_table rules suggest we should have one. There is a lot
* of daylight between where we will create a TOAST table and where
* one is really necessary to avoid failures, so small cross-version
* differences in the when-to-create heuristic shouldn't be a problem.
* If we tried to create a TOAST table anyway, we would have the
* problem that it might take up an OID that will conflict with some
* old-cluster table we haven't seen yet.
*/

I don't really see any near-term reason why we would need to change this.

In the long run, it would certainly be cleaner if pg_upgrade dropped
the force-the-relfilenode-assignment approach and instead remapped
relfilenodes from old cluster to new. But I think it's just for
cleanliness rather to fix any live or foreseeable bug.

regards, tom lane