Summary
In this chapter, we have discussed some of the possible concurrency problems that can occur in a multiuser database environment. To protect the data as it is being modified, rules are established and the changes are grouped together in transactions.
The data updated by a transaction is either made permanent by the COMMIT statement or removed using the ROLLBACK statement. Each transaction is made up of one or more SQL statements. The rules of concurrent data access are determined by the isolation level, which is set for static and dynamic SQL application modules.
DB2 implements the isolation level semantics of data access by implicitly acquiring locks on behalf of the applications. Applications can decide to lock a resource for EXCLUSIVE ...
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