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. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
