Re: pgsql: Fix "base" snapshot handling in logical decoding

Hi Arseny. I'm writing a commit message to push this test change, and I
can't explain this bit:

On 2018-Jul-02, Arseny Sher wrote:

> 3) As a side note, answer to my question 'why do we get different errors
> with VACUUM and VACUUM FULL' is the following. With VACUUM FULL, not
> only old pg_attribute entry is pruned, but also xmin of new entry
> with attisdropped=true is reset to frozen xid. This means that
> decoding session (RelationBuildTupleDesc) actually sees 3 attributes,
> and the fact that one of them is dropped doesn't embarrass this
> function (apparently relnatts in pg_class is never decremented) --
> we just go ahead and decode only live attributes.

I just don't see it that VACUUM FULL would change the xmin of anything
to FrozenXid, and in my experiments it doesn't. Did you mean VACUUM
FREEZE?

PS - sorry about the broken CC I added :-(

--
Álvaro Herrera https://www.2ndQuadrant.com/
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