RE: MultiMaster Replication

As Chris mentions, multi-master replication is inherently a tightly coupled replication solution. As such, it is probably not appropriate to try to force multi-master replication into the sort of setup you are describing.  

One solution, assuming you are using 9i or later, would be to use Streams to propagate DML changes between the systems. Streams is message-based and asynchronous, so it is inherently loosely coupled. Streams sends a logical change record (LCR) which the destination system can transform before applying-assuming you wrote the appropriate transformation routines, you could have one system running v1 of the schema definition and another system running v2. (Whether this is a good idea and whether you really want to write the routines to transform the data going in both directions is another question). I suspect that it will be a lot easier to fit a Streams-based solution into the parameters you describe than one based on multi-master replication.  

Justin Cave

Distributed Database Consulting, Inc.

http://www.ddbcinc.com/askDDBC  

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Marquez, Chris Sent: Wednesday, August 24, 2005 12:11 PM To: fuadar_at_fuadarshad.com; oracle-l_at_freelists.org Subject: RE: MultiMaster Replication    

Not to be negative and not to total disregard your request for technical help but;

>>4. the business does not want these system to be tightly coupled.

Oracle Multi Master Replication is by definition creating dependences between to nodes/databases.
They will forever be "tightly coupled" when implementing Oracle Multi Master Replication

>>5. if the 2 systems are disconnected we might need to change
information on any or both systems.
I have had to "fight" with Oracle Multi Master Replication to "let go" of replication depends when the Master Def Site was lost. I tried in vain to drop objects and change the Master Def Site. Life is definitely better when the two database can talk happily with each other.

hth

Chris Marquez
Oracle DBA

-----Original Message-----
From: Fuad Arshad [mailto:fuadar_at_yahoo.com] Sent: Wed 8/24/2005 9:37 AM
To: Marquez, Chris; oracle-l_at_freelists.org Subject: RE: MultiMaster Replication

Chris/List
let me try to explain the problem i'm trying to solve. 1. 2 systems same structure intially but software upgrade done seperately might cause structures not to be in sync. 2. uptime requirements for one node but not the other might cause the fact that we lose the master definition site(network connectivity) while the other server is failed over to a hot site. 3. there is transformation happening i.e sequences are different on both nodes.
4. the business does not want these system to be tightly coupled. 5. if the 2 systems are disconnected we might need to change information on any or both systems.

"Marquez, Chris" <cmarquez_at_collegeboard.org> wrote:

>>1....there needs to be a master definition site.
>>if the communication breaks between 2 sites
>>will we have to change the master definition site.

It is possible to change the "master definition site", but generally this would only be done of the original master definition site is "gone", "dead", "lost"...temporary loss of one multi-master site does not mean re-defining the master definition site...unless you need to do repadmin tasks that must be done for the (down) master definition site.

>>2...replicate sequences

I used local sequence on each side the would *not* collide buy using different START and INCREMENT values.

I liked Oracle Multi Master Replication for *simple* TABLE level replication where most or all transaction happen on one node...more than that and the admin of it (any transaction based replication) becomes painful.

hth

Chris Marquez
Oracle DBA

-----Original Message-----
From: oracle-l-bounce_at_freelists.org on behalf of Fuad Arshad Sent: Sun 8/21/2005 10:19 AM
To: oracle-l_at_freelists.org
Subject: MultiMaster Replication

I've been reading up on multimaster replication and had a few questions.

1. After the multimaster replication setup there needs to be a master definition site. if the communication breaks between 2 sites will we have to change the master definition site.
2. the tables the i'm trying to replicate have sequences that i need to transform to sequences on the other side.

oracle seems to say its possbile but i cant find an example.

If anyone on the list has had experience with multimaster. if they could drop me an email and we could chat a little bit offline that would be really great.

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