Re: The vacuum-ignore-vacuum patch

Hannu Krosing wrote:
> ?hel kenal p?eval, N, 2006-07-27 kell 22:05, kirjutas Bruce Momjian:
> > Another idea Jan had today was whether we could vacuum more rows if a
> > long-running backend is in serializable mode, like pg_dump.
>
> I don't see how this gives us ability to vacuum more rows, as the
> snapshot of a serializable transaction is the oldest one.

Good question. Imagine you have a serializable transaction like
pg_dump, and then you have lots of newer transactions. If pg_dump is
xid=12, and all the new transactions start at xid=30, any row created
and expired between 12 and 30 can be removed because they are not
visible. For a use case, imagine an UPDATE chain where a rows was
created by x=15 and expired by xid=19. Right now, we don't remove that
row, though we could.

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

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