From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Arseny Sher <a(dot)sher(at)postgrespro(dot)ru> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: pgsql: Fix "base" snapshot handling in logical decoding |
Date: | 2018-07-05 18:22:32 |
Message-ID: | 20180705182232.3n7ih4kyhtwhmvod@alvherre.pgsql |
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Lists: | pgsql-committers pgsql-hackers |
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/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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