What is a deadlock in DB2 and how can it be resolved?

A deadlock in DB2 occurs when two or more transactions are waiting for each other to release locks on resources held by the other, resulting in a situation where neither transaction can proceed. This can happen when multiple transactions are trying to access the same resources in a different order, leading to a circular dependency.

To resolve a deadlock in DB2, there are several strategies that can be used:

1. Transaction Timeout: Setting a timeout for transactions can help prevent deadlocks by automatically canceling transactions that have been waiting for too long.
2. Deadlock Detection: DB2 has built-in deadlock detection mechanisms that can identify and resolve deadlocks by rolling back one of the transactions involved.
3. Lock Size and Duration: Optimizing the size and duration of locks can reduce the likelihood of deadlocks by minimizing the time that resources are held and reducing the chances of conflicts.
4. Retry Logic: Implementing retry logic in applications can help to handle deadlocks by reattempting transactions that have been rolled back due to deadlock situations.

By following these strategies and understanding the causes of deadlocks in DB2, developers can effectively mitigate the risk of deadlocks and ensure the smooth operation of their database applications.