On Nov11, 2011, at 16:18 , Robert Haas wrote: > In the extend query protocol scenario, it seems to me that keeping the > snapshot would be both wrong and a bad idea. It would be wrong > because the user will (I think) expect the query can see all rows that > were marked as committed prior to Execute message. It would be a bad > idea because we'd have to keep that snapshot advertised for the entire > time between Parse and Execute, even if the client was sitting there > doing nothing for a long time, which would hold back RecentGlobalXmin.
Hm, but that'd penalize clients who use the extended query protocol, which they have to if they want to transmit out-of-line parameters. You could work around that by making the extended protocol scenario work like the simply protocol scenario if the unnamed statement and/or portal is used. Since clients presumably use pipelined Parse,Bind,Execute messages when using the unnamed statement and portal, they're unlikely to observe the difference between a snapshot taken during Parse, Bind or Execute. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers