Florian G. Pflug escribió:
> Hannu Krosing wrote:
> >Ühel kenal päeval, P, 2007-02-18 kell 14:27, kirjutas Joshua D. Drake:
> >>Hannu Krosing wrote:
> >>>Ühel kenal päeval, L, 2007-02-17 kell 22:49, kirjutas Chad Wagner:
> >>>To get a flashback query, you "just" have to construct a snapshot from
> >>>that time and you are done. We don't store transaction times anywere, so
> >>>the flashback has to be by transaction id, but there is very little
> >>>extra work involved. We just don't have syntax for saying "SELECT ... AS
> >>>SEEN BY TRANSACTION XXX"
> >>Well this is certainly interesting. What do we think it would take to
> >>enable the functionality?
> >
> >First we must run the query in serializable mode and replace the
> >snapshot with a synthetic one, which defines visibility at the start of
> >the desired transaction
> >
> >probably it is a good idea to take a lock on all tables involved to
> >avoid a vacuum to be started on them when the query is running.
> Would the xmin exported by that transaction prevent vacuum from removing
> any tuples still needed for the flashback snapshot?
Sure, and that makes the mentioned lock unnecessary.
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Alvaro Herrera http://www.CommandPrompt.com/
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