Excerpts from Richard Walker's message of jue may 20 02:19:17 -0400 2010:
> (a) (ii) It seems a breach is possible via the xmin values.
> In that case, what about doing updates inside a transaction
> that does a trivial update of all rows, e.g.:
> begin transaction;
> update mytable ....; -- change one row
> update mytable set id=id; -- change all rows
> commit;
> So now all rows have the same xmin values.
> Does this work? Performance is not so good, is it?
> Is there a better way?
The easiest way to do this is probably VACUUM FREEZE.
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