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# Technical Challenges

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The current trend toward multitiered Web applications makes the two-tier architecture less common in production systems, but no less viable. Because there is no shared cache in a two-tier system, you risk encountering stale data if you run multiple instances of the application. This risk increases as the number of individual database sessions increases.

To minimize this problem, TopLink offers support for several data locking strategies. These include pessimistic locking and several variations of optimistic locking. For more information, see "Configuring Locking Policy".