Hi David,

I am not sure where you can find merge replication for MySQL but I
would be most interested to know where it is available. According to
the official manual for version 5.xx found here: (http://dev.mysql.com/
doc/refman/5.0/en/replication.html) there is no support for merge.

Jet replication is quite good as a concept, but it is not really a
comparable replication system to that of SQl Servers' merge
replication although the end reuslt may be similar (or even the same).
The mechanics of it are completely different in its implementation -
as one would expect from Jet vs SQL Server.

Postgres I havent looked at for quite a while either. I think the
merge replication option there was available as a paid for third party
add-in, or perhaps from the commercialised version called BizGres.
From what I can recall it still lacked the features like subscription
and permissions controls that SQL Server has. It was more of a multi-
master type scenario that one might use for failover purposes.

The only other one that I have seen that comes close is from Oracle,
but I am not qualified to comment on just how good it really is or how
it actually functions. Some of the DB Admins at a former workplace
were playing with something approximatling merge replication for a
sales field force application. I do not know the outcome or specifics
but on the surfcae it seemd quite similar. Since I am not a big Oracle
fan I never pursued the topic.

I was not aware that the Jet replication team was / is the same team
that did replication for SQL Server. Makes sense I suppose. Does that
mean they are from the original Sybase side of things? Thats going
back a long way indeed.

That being said, I stand by my original statement that merge
replication is a great strength IMO of SQL Server, and is in fact not
common in the industry even amongst enterprise class database servers.
Some forms of replication are, but merge is definitely a bit more
special and rare to find. If you are aware of a merge replication
option for MySQL would you be so kind as to post a link to it?

Cheers

The Frog

David wrote:

The Frog <mr.frog.to.you (AT) googlemail (DOT) com> wrote in
news:e5290de2-7b0d-4960-a5d0-63caeefa0d99 (AT) cu4g2000vbb (DOT) googlegroups.co
m:

Well, you're right on that! I just assumed that any other kind of
replication was not worth implementing in this day and age, since
the aim of server replication is redundancy, and you need identical
databases (which requires merge replication).

The mechanics are different, of course, but it's real merge
replication, in that it allows multi-master editing and merging of
changes from multiple databases. Yes, it has its problem, and yes,
it's fading into the background, but it was there long before many
big iron databases had it.

While the mechanism for merge replication with Jet is certainly
different than SQL Server, a large portion of the problems one
encounters in implementing a solution are going to be the same (so
much so that SQL Server and Jet shared a conflict resolver for a
while, for instance; as well as the fact that for one version of SQL
Server (2000), a Jet database could participate as a partner in the
replica set).

Third-party merge replication has been available for many databases
for a very long time. I looked at various options for it as long ago
as 1998.

Er, I think you're using "multi-master" here in a non-standard way.
"Multi-master replication" is something of a synomym for "merge
replication" (i.e., edits at multiple databases, with changes
mergeable so that all databases are theoretically one synch away
from identical).

As someone who has been implementing Jet Replication solutions since
1998, I find it rather unimpressive, to be honest. Yes, I recognize
that what these big-iron databases are doing is both more
complicated and more robust than what Jet Replication offers, but
the fact is, Jet Replication offered something long before all of
these and it was quite useful, and when properly cared for and
administered, quite reliable.

Not the same team, but a large portion of the people moved over to
the team that built SQL Server 2000 (or was it 7 that first
implemented replication?).

Nope. They were Jet people. Sybase didn't have replication, so far
as I know.

But it's not something remarkable in the sense of being worthy of
pointed out as a key feature that is unlike any other database. It
may have ease-of-use advantages, or additional features, but you
singled it out in a way that made it seem like you thought it was
something new or particularly innovated. From my point of view, it's
completely old hat!

Really? Oracle has it, other than MySQL (which I hesitate to
classify among enterprise-class db servers) what others don't have
it?

From my point of view, any form of replication that is not merge
replication is not really replication -- it's just log shipping.
While master/slave replicas have their place, they don't really
address the load balancing issues that I thought enterprise-level
replication was supposed to be for.

But my viewpoint is warped by my early and long Jet Replication
experience, where I kind of assumed that if the lowly Jet db engine
could do it, it's surely doable by the big iron. I really should
know better.

--
David W. Fenton http://www.dfenton.com/
contact via website only http://www.dfenton.com/DFA/