Adaptive Server protects the tables, data pages, or data rows currently used by active transactions by locking them. Locking is a concurrency control mechanism: it ensures the consistency of data within and across transactions. Locking is needed in a multiuser environment, since several users may be working with the same data at the same time.
Locking affects performance when one process holds locks that prevent another process from accessing needed data. The process that is blocked by the lock sleeps until the lock is released. This is called lock contention.
A more serious locking impact on performance arises from deadlocks. A deadlock occurs when two user processes each have a lock on a separate page or table and each wants to acquire a lock on the same page or table held by the other process. The transaction with the least accumulated CPU time is killed and all of its work is rolled back.
Understanding the types of locks in Adaptive Server can help you reduce lock contention and avoid or minimize deadlocks.
