On "multi-master" (was: Limitations of PostgreSQL)

On Thu, Oct 13, 2005 at 10:46:29AM -0500, Scott Marlowe wrote:
> choice in another. So, multi-master replication isn't likely to become
> a plug in module for postgresql any time soon.

It's not even a thing, so it can't become a plug-in.

Consider just two kinds of multi-master:

1. Oracle's RAC. This is a shared-disk, engine-failover kind of
multi-master. It provides a certain amount of scaling, but nothing
I've seen or heard suggests that the license cost couldn't just as
easily and effectively be thrown at larger hardware for better
scaling. The really big reason to use RAC is five-nines situations:
you're trying to make sure that even unlikely failures of your
machines never cause the database to stop working (for suitably
lawyer-understood values of "stop". RAC remastering is not a
zero-cost, nor even invisible, operation. But from an application
perspective, it can be made to look like "database is slow" as
opposed to "database crashed").

2. Disconnected sales forces with local copies of some portion
of the sales database. This is completely distributed database use,
with potential for conflicts and an associated need for conflict
resolution strategies.

These are different sorts of systems addressing completely different
use cases. But they're both potentially marketed as "multi-master".
Often, a manager asking for multi-master thinks s/he is buying all of
this; which desire is probably impossible to satisfy with one piece
of software (as opposed to one thing all called by the same name by
the marketing department).

A

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