Bruce Momjian wrote > Oh, OK, it sounds fine. The user really doesn't choose what timeline to > see --- rather, it is the current xid at the time they take their > snapshot and other running xids that controls that. You can control > your transaction isolation level, but that only controls how often you > take snapshots.
^ This kind of makes my point. You've described perfectly the mechanics of the system but from a mostly black-box perspective a user-decision (choosing the isolation level) directly impacts which point-in-time (xid) is chosen for the snapshot behind a particular SQL statement. The fact they can only choose between two pre-defined and relative points-in-time is a detail to explain later but the fact is they are required to make such a choice (one is provided by default but still one chooses - even if through ignorance - to use the default) as an outcome of MVCC should be included - in some form - in the introduction. In the current, proposed, and my revisions it is indeed covered but to various degrees of detail and low/high level focus. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/MVCC-snapshot-timing-tp5777759p5778039.html Sent from the PostgreSQL - docs mailing list archive at Nabble.com. -- Sent via pgsql-docs mailing list (pgsql-docs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs
