"Tom Lane" <[EMAIL PROTECTED]> writes: > Gregory Stark <[EMAIL PROTECTED]> writes: >> Uhm, yeah, I somehow didn't write was I was thinking. I didn't mean to say we >> would be taking a new snapshot for each INSERT but that we would be resetting >> xmin for each INSERT. Whereas currently we only set xmin once when we set the >> serializable snapshot. > > Right, but setting xmin within GetSnapshotData is essentially free. > What I'm envisioning is that we lose the notion of "this is a > serializable snapshot" that that function currently has, and just > give it the rule "if MyProc->xmin is currently zero, then set it". > Then the only additional mechanism needed is for the snapshot > manager to detect when all snapshots are gone and zero out > MyProc->xmin --- that would happen sometime during command shutdown, > and per current discussion it shouldn't need a lock.
It would be nice if there was some way to notice that no other transactions have committed since last we calculated a snapshot and just reuse that snapshot. I would say ideally before we throw out our xmin but I suspect the point of synchronization needed to notice this condition would be tantamount to that same lock anyways. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's RemoteDBA services! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
