From: | David Johnston <polobo(at)yahoo(dot)com> |
---|---|
To: | pgsql-docs(at)postgresql(dot)org |
Subject: | Re: MVCC snapshot timing |
Date: | 2013-11-13 01:49:00 |
Message-ID: | 1384307340948-5778039.post@n5.nabble.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-docs pgsql-hackers |
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.
From | Date | Subject | |
---|---|---|---|
Next Message | Peter Eisentraut | 2013-11-13 11:56:04 | Re: misleading lang_name case in CREATE FUNCTION doc. |
Previous Message | Bruce Momjian | 2013-11-13 01:39:35 | Re: MVCC snapshot timing |
From | Date | Subject | |
---|---|---|---|
Next Message | Peter Eisentraut | 2013-11-13 02:01:33 | Re: [COMMITTERS] pgsql: Replace duplicate_oids with Perl implementation |
Previous Message | Craig Ringer | 2013-11-13 01:42:13 | Re: Information about Access methods |