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  Oracle Replication Tips by Burleson

Oracle replication Assigning a Prefix Based on Site

A more flexible (and scalable) approach is to have all sites start their sequence at 1 and add a site prefix to the sequence number to generate the key.  At NAVDB.WORLD, the first three rows created would have the keys navdb1, navdb2, and navdb3.  At the master site MYDB.WORLD, the first three would be mydb1, mydb2, and mydb3.  As these rows are propagated none of the keys will collide. 

In real life, keys are not always created on sequences.  In cases such as the author_key column in the PUBS schema, you may need keys generated from a central location.  All master sites obtain their keys for that table from the central repository.  You must either require that only that site creates the records or create a procedure on the remote site that will fetch the next key from the depository.  For efficiency, you could create a trigger that pre-fetches a number of keys and places them in a table and provides them as needed on the local site, fetching additional keys as needed. 

It is always a much better solution to use the natural key of the table, if one exists, rather than a derived key. A natural key can avoid a great deal of trouble.

As you can see, conflict avoidance must be part of your replication planning.  Once the replication environment has been created and is operating, it is much harder to avoid conflicts.  Also, insure that your conflict avoidance method is flexible enough to handle adding and removing master sites. 


This is an excerpt from Oracle Replication By Rampant TechPress (only $19.95).  You can click here to order a copy and get instant access to the code depot:

http://www.rampant-books.com/book_2003_2_replication.htm


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