The promise of distributed databases has been with us a long time. Until relatively recently, though, the technology available to set up a distributed database was either too limited or too complicated. Today, database replication, the copying and maintenance of data on multiple servers, has come of age. Every major database vendor has a replication solution of one kind or another, and many nondatabase vendors also offer alternative methods for replicating data.In this article, I look at three of the top databases and compare their replication technology. For various reasons, I have chosen to look at replication solutions from Microsoft Corp. Redmond, Wash., Oracle Corp. Redwood Shores, Calif., and Sybase Inc. Emeryville, Calif. Other database products, including those from Informix Software Inc. Menlo Park, Calif., IBM Corp. Armonk, N.Y., and Computer Associates International Inc. Islandia, N.Y., have advanced replication technology, and you can build solid replication architectures with middleware products such as those from Tuxedo and TopEnd. Before I look at descriptions of the three different approaches, though, it would be worthwhile to discuss some of the issues with replication.

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