Unisys OS 2200 databases: Difference between revisions

Revision as of 15:16, 31 July 2009

Revision as of 18:31, 2 August 2009

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The database managers are implemented as a [[Unisys OS 2200 operating system#Subsystems|protected subsystem]] and are called as a procedure from user programs and other subsystems. The implementation as a subsystem means that theirthere is no upper limit to the potential concurrency of activities (threads) executing in the database manager. The thread of each user executes the database manager code but within its protection ___domain so that misbehaved and malicious programs cannot affect the integrity of the database. This approach also reduces the path lengths and overhead involved as messages do not have to be sent between the caller and the database manager. All communication is through parameters.

This commonality has made it possible for clients to modernize applications moving from language files, to a network database, to a relational database. They can use a mixture of these at the same time in a single program while retaining full recoverability. With all the recovery, clustering, locking, and cache management centralized, applications do not have to deal with those aspects. In OS 2200 locking is generally implicit in the database verbs used. For example, a read-for-update implies setting a certain type of lock and the corresponding update write implies clearing it.