RE: Oracle MAA and active-active replciation between site
Date: Fri, 1 Aug 2008 13:56:50 +0300
The big concern about the application in replication environment are the conflicts.
- You should in all ways avoid updating or deleting the same row of a table from both sites at the same time.
- The same for the inserts. Your application should not be able to insert rows with the same primary key values from both sites. E.g. if you have primary keys generated by sequence, one of the sites should start with 1 increment by 5 and the other will start with 2, increment with 5.
- You must have primary key on all tables. This is not mandatory from the docs, but it is always good practice, even without replication.
- You should design all triggers carefully - when there is an insert in a table on one site, the trigger may make some things like inserting/updating/deleting on other tables. Then when this is replicated to the other site, there will be insert again, but the trigger should not fire again.
- When there is a conflict, a whole transaction is not replicated. Even if you do not care for this problematic row in this table, a conflict on a row of a table will block the whole transaction and you have to resolve it.
- If you decide to let the replication of all following transactions be done in spite of the conflicts, you may have lots of anomalies in the data. In the other hand, resolving a conflict may take some time and you may not want to block the whole replication because of a single problematic transaction
Oracle Certified Master
From: Pradeep Chetal [mailto:Pradeep.Chetal_at_mformation.com] Sent: Friday, August 01, 2008 12:56 PM
To: Yavor Ivanov
Subject: RE: Oracle MAA and active-active replciation between site
In terms of wise application design, what do you recommend?
What are the big 3-4 things we should worry about?
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Yavor Ivanov Sent: Friday, August 01, 2008 3:05 AM
To: Pradeep Chetal; oracle-l_at_freelists.org Subject: RE: Oracle MAA and active-active replciation between site
I've done one project active-active replication using oracle's Advanced replication. There is good documentation about this.
There are 2 basic problems with this - The conflicts. You will always have conflicts onactive-active replication. Most of them can be avoided by wise application and process design, but it will need lot of thinking. And you will still have conflicts you cannot avoid and cannot resolve automatically
- The burden. It is much harder for administration. Adding a simple column is pain in the ass, Yes, there are procedures, but still... It is hard. But it really works - for 2 years now. I would consider this.
I also have done it with "Basic replication", master - (updateable) mvews with 12 active sites across the country (one master in HQ). But it is even harder to support this than Advanced replication. And the application on this project was specially built with the replication in mind. It works for 9 years now (we started it on 8.1.5, now all the servers are 10.2). But I would never advise this approach, this is aged and arcane thing.
Oracle Certified Master
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Pradeep Chetal Sent: Thursday, July 31, 2008 6:18 PM
Cc: Pradeep Chetal
Subject: Oracle MAA and active-active replciation between site Importance: High
Oracle has an MAA with
However, one of our clients would like to have active-active replication between remote sites, so that each site can be used.
Have you done this? What software did you use?
Also, what are the limitations on schema, if any to do this?
Thanks in advance,
Sr. Director - Infrastructure Architecture
Mformation Technologies Inc.
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