Re: Global snapshots

On Tue, May 1, 2018 at 12:27 PM, Stas Kelvich <s.kelvich@postgrespro.ru> wrote:
> Here proposed a set of patches that allow achieving proper snapshot isolation
> semantics in the case of cross-node transactions. Provided infrastructure to
> synchronize snapshots between different Postgres instances and a way to
> atomically commit such transaction with respect to other concurrent global and
> local transactions. Such global transactions can be coordinated outside of
> Postgres by using provided SQL functions or through postgres_fdw, which make use
> of this functions on remote nodes transparently.

I'm concerned about the provisioning aspect of this problem.  Suppose
I have two existing database systems with, perhaps, wildly different
XID counters.  On a certain date, I want to start using this system.
Or conversely, I have two systems that are bonded together using this
system from the beginning, and then, as of a certain date, I want to
break them apart into two standalone systems.  In your proposed
design, are things like this possible?  Can you describe the setup
involved?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company