>> I don't see any way around the fact that when a tuple is removed, it's >> gone and can't be accessed by queries. Either you don't remove it, or >> you kill the query. > > Actually we came up with a solution to this - use filesystem level > snapshots (like LVM2+XFS or ZFS), and redirect backends with > long-running queries to use fs snapshot mounted to a different > mountpoint. > > I don't think Simon has yet put full support for it in code, but it is > clearly _the_ solution for those who want to eat the cake and have it > too.
I think _the_ solution is to notice when you're about to vacuum a page that is still visible to a running backend on the standby, and save that page off to a separate cache of old page versions (perhaps using the relation fork mechanism). I suspect filesystem-level snapshots can be made to work, but it's never going to be a portable solution, and I suspect you're going to need a lot of the same bookkeeping anyway (like, when you have page X in shared buffers, which version of page X is it, anyway?). ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
