Replication in SQL

I'm not completely sure what you mean by replicating in SQL, are you talking about Microsoft's SQL 7.0 database or just SQL in general. Microsoft does provide replication for SQL database products. It is an additonal purchase, info at www.microsoft.com. Most replication involves using the log files of the parent database which is used to roll-forward transaction changes into the child or replicated database. Depending on how current you need the replicated server to be, you could perform your transactions on the main server, extract the data at given points and load that data into the replicated server through a batch update. The best way is to buy the replication package for the database you are using. There are issues in replication such as confirmation of a commit that these systems have been built to address. Each manufacturer will have more detail on there websites for database specific solutions.

Most replication packages rely on parsing the log file. This works well, but it has its limitations. Also - Most replicaiton scenarios are of the hub-and-spoke variety.
Case in point: Retail stores. The store is the originator of the records, while headquarters simply consolidates this information. HQ is initially empty, and it is tough to get the remote stores to send all of their existing data, as the log file entries for the inserts are long gone. Additionally, in a retail environment, there are a large amount of updates to the same record (as in quantity on hand). The log based replication method would have to repeat all of the transactions. So for instance, you started the day out with a qty on hand of 100, by the end of the day you're down to 10. If you sold all 90 one-at-a-time, you're looking at 90 transactions just for one item in inventory. Not very efficient. There is a company based in Canada - Peer Direct - with a replication package that works great and is notlog based. It is expensive, but you get what you pay for! If price is a concern, then investigate Sybase's Adaptive Server Anywhere (formerly SQL Anywhere). It is a good datbase with a small footprint and has built-in log-based replication.
Regards,
-Mike

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