Re: Future In-Core Replication

On Thu, Apr 26, 2012 at 01:41:33PM +0100, Simon Riggs wrote:
> Some people have talked about the need for "multi-master replication",
> whereby 2+ databases communicate changes to one another. This topic
> has been discussed in some depth in Computer Science academic papers,
> most notably, "The Dangers of Replication and a Solution" by the late
> Jim Gray. I've further studied this to the point where I have a
> mathematical model of this that allows me to predict what our likely
> success will be from implementing that. Without meaning to worry you,
> MM replication alone is not a solution for large data or the general
> case. For the general case, single master replication will continue to
> be the most viable option. For large and distributed data sets, some
> form of partitioning/sharding is required simply because full
> multi-master replication just isn't viable at both volume and scale.
> So my take on this is that MM is desirable, but is not the only thing
> we need - we also need partial/filtered replication to make large
> systems practical. Hence why I've been calling this the
> "Bi-Directional Replication" project. I'm aware that paragraph alone
> requires lots of explanation, which I hope to do both in writing and
> in person at the forthcoming developer conference.

I would love to see a layout of exactly where these things make sense,
similar to what we do at the bottom of our documentation for "High
Availability, Load Balancing, and Replication":

http://www.postgresql.org/docs/9.1/static/different-replication-solutions.html

Users and developers just can't seem to get the calculus of where things
make sense into their heads, me included.

For example, you said that "MM replication alone is not a solution for
large data or the general case". Why is that? Is the goal of your work
really to do logical replciation, which allows for major version
upgrades? Is that the defining feature?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +