On 2/9/2007 2:27 PM, Richard Troy wrote:
In general terms, "blending of replication [techniques]" means to me that
one can have a single database instance serve as a master and as a slave
(to use only one set of terminology), and as a multi-master, too, all
simultaneously, letting the DBA / Architect choose which portions serve
which roles (purposes). All replication features would respect the
boundaries of such choices automatically, as it's all blended.

That is specifically what the changes to pg_trigger and pg_rewrite take into account. However much you blend different techniques, a single transaction on one server will always fall into one of three categories. 1) It could be the original operation done by the client application. B) It could be the actions performed by the replication engine to replay a remote transaction. And iii) it can be an administrative operation that requires not to be propagated at all.

No matter how many different models you have in parallel, one single transaction will be either a master, a slave or an isolated local thing. The proposed changes allow to tell the session which of these three roles it is playing and the triggers and rules can be configured to fire during master/local role, slave role, always or never. That functionality will work for master-slave as well as multi-master.

Although my current plan isn't creating such a blended system, the proposed trigger and rule changes are designed to support exactly that in a 100% backward compatible way.


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