Re: Replication accross a WAN

On Thu, 21 Oct 1999 22:54:54 +1000, "Dave Waterworth" <pscdaw_at_ihug.com.au> wrote:

>Hi
>
>Could anyone point me towards resources detailing standard Oracle techniques
>for replicating accross a low(ish) bandwidth wide area network. We want to
>keep two databases in synch. Synchronous replication is not critical, but
>replication must be bi-directional (i.e. inserts on db1 replicated to db2
>and inserts on db2 replicated to db1 simultaneously). Are there robust, cost
>effective commercial packages available? Is it more effective to write your
>own scheme based on expert knowledge of the schema and applications?
>
>Currently the proposal is to write our own. One things that's bugging me is
>that the data in each database is meant to be identical, including fields
>that are modified by triggers, (setting last modified field to sysdate,
>primary key to a sequence numver etc.). But how do you keep the sequences in
>step? If sequence is initially in step and a different record is inserted at
>each site, the different records will end up with the same sequence number?
>
>Any comments will be appreciated
>
>Dave Waterworth
>
>Power Systems Consultants New Zealand Ltd
>

Have you already browsed through the Oracle Docs on methods of replicating data - Distributed Data Volumes 1 and 2 ?

There is a lot of information detailing methods you can use to implement and tune replication. For instance, you could use  Advanced Replication or Updateable Snapshots to work with data being updated by both sites. Advanced Replication seems to be the closest solution to what you want to achieve (n-way replication).

The date and sequence synchronization is a known issue that has been covered in a few places , such as the Metallic Press Tuning and Administration Book. For sequences, it is suggested to partition values - ie, have values at one site be even and the other be odd or use prefixes. For dates, it is suggested to use a common system time for both sites, if across time zones - either choosing the local time of one of the databases or using an agreed time such as GMT.

Lisa Hudd
e-DBA Limited Received on Thu Oct 21 1999 - 11:54:13 CDT