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Updates and Work Units
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Updates from Multiple TargetsAll durable data changes in a Cloudscape synchronization system are handled at the source. Since source data replaces target data after the refresh operation, the normal multi-user concurrency and transaction control mechanisms of the source database prevent the synchronized system from becoming inconsistent. The target "screens" the transactions sent to the source: if a transaction fails at the target, it is not sent to the source at refresh time. Since target and source data are usually not very different, updates that succeed at the target usually succeed at the source as well. Of course, provisional transactions that succeed at the target can still fail at the source. This typically occurs because another target has changed the source data since this target's last refresh. For example, an update from a different target may have reduced inventory enough to cause the current transaction to violate a source check constraint. (An update from a target can also fail if the system administrator or other user has updated the source database directly.) Transactions are in conflict if applying both of them at the source would violate a database consistency rule. Conflicts are simpler to manage in Cloudsync than in many other synchronized systems. Cloudsync's hub-and-spoke topology allows conflicts to be resolved between a single target and the source, rather than among multiple databases. This is similar to how updates are handled in a centralized client/server application. Transaction failure is not the only issue when data changes come from many targets. You may want to specify how changes should be handled even when they don't fail. For example, you may want to send a message when an update causes inventory to drop too low, even if no transaction has yet failed. The rest of this chapter shows the simple, robust way that Cloudsync provides to handle updates that come from different parts of the system. |
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![]() Cloudscape Version 3.6 For information about Cloudscape technical support, go to: www.cloudscape.com/support/.Copyright © 1998, 1999, 2000 Informix Software, Inc. All rights reserved. |