"Zeugswetter Andreas ADI SD" <[EMAIL PROTECTED]> writes: >> 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 > > We could use something that controls "global xmin". > It would ensure, that global xmin does not advance bejond > what still needs to be visible. This would probably be a > sliding time window, or a fixed point in time that is > released by the dba/user.
Well there's another detail you have to cover aside from rolling back your xmin. You have to find the rest of the snapshot including knowing what other transactions were in-progress at the time you want to flash back to. If you just roll back xmin and set xmax to the same value you'll get a consistent view of the database but it may not match a view that was ever current. That is, some of the transactions after the target xmin may have committed before that xmin. So there was never a time in the database when they were invisible but your new xmin was visible. I think to do this you'll need to periodically record a snapshot and then later restore one of those saved snapshots. Not sure where would be a good place to record them. The WAL seems like a handy place but digging through the WAL would be annoying. Incidentally this is one of the things that would be useful for read-only access to PITR warm standby machines. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
