On 1/06/2011 4:52 AM, Pete Chown wrote:
Is there a solution to this, or is the point that I'm simply asking too much? Perhaps the Java EE container is not promising consistency in the sense I'm talking about.
Distributed transactions will give you atomicity if done right - with two-phase commit (2PC) - but AFAIK will *NOT* give you consistency across the databases in question. You have to ensure consistency yourself, usually by locking data or taking snapshots.
If you want strong consistency guarantees between certain data, try to keep them in the same database. If you can't, you may need to be prepared to (try to) do your own consistency enforcement using application-coordinated record or table locking.
There are scaling limits to keeping things in one database on one machine, which is why some database vendors offer multi-master setups. Pg doesn't, at present. That said, multi-master configurations have their own performance and scalability problems because providing consistency across a distributed multi-machine database adds a lot of overhead. They can be made to be faster than a single machine setup, but (from what I've heard; I have no direct experience here) you usually have to throw lots of hardware at them and use low-latency interconnects.
-- Craig Ringer Tech-related writing at http://soapyfrogs.blogspot.com/ -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
