Dimitri Fontaine <[EMAIL PROTECTED]> writes: > Le mercredi 26 mars 2008, Tom Lane a écrit : >> whenever the number of active snapshots goes to zero
> Does this ever happen? Certainly: between any two commands of a non-serializable transaction. In a serializable transaction the whole thing is a dead issue anyway, since the original snapshot has to be kept. There are corner cases involving open cursors where a snapshot might persist longer, and then the optimization wouldn't apply. The formulation that Alvaro gave would sometimes be able to move xmin forward when the simple no-snaps-left rule wouldn't, such as create cursor A, create cursor B (with a newer snap), close cursor A. However I really doubt that scenarios like this occur often enough to be worth having a much more expensive snapshot-management mechanism. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers