Simon Riggs wrote:
On Thu, 2008-08-07 at 14:18 +0100, Richard Huxton wrote:
An attempt to write to user_emails by T0 will fail with an error.
All above correct
The point of doing this is that *if* T0 becomes the oldest transaction
it will *not* interfere with removal of rows on "user_emails".
An attempt to read from user_emails by T0 will be allowed?
No, reads must also be excluded otherwise MVCC will be violated.
Ah good - I was wondering, but I read your first email as allowing reads.
What happens if I'm in ISOLATION LEVEL SERIALIZABLE? Presumably the read
is disallowed then too?
No, that's not relevant. That is your choice about how often you update
your snapshot of the database. The visibility group refers to the
*scope* of the snapshot, so the two things are orthogonal.
So - effectively we're partitioning the database into (possibly
overlapping) subsets of tables.
Would it simplify things at all to have a centrally-defined list of
"visibility scopes" (or "groups") which your transaction/user can
access? As a DBA, I'd rather have somewhere central to manage this, and
I'd probably make it per-user anyway.
--
Richard Huxton
Archonet Ltd
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
