Centralized and distributed wait depth limited concurrency contr

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364DIG1, 3642814, 3642821, G06F 1540

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active

051931885

ABSTRACT:
A wait depth limited concurrency control method for use in a multi-user data processing environment restricts the depth of the waiting tree to a predetermined depth, taking into account the progress made by transactions in conflict resolution. In the preferred embodiment for a centralized transaction processing system, the waiting depth is limited to one. Transaction specific information represented by a real-valued function L, where for each transaction T in the system at any instant in time L(T) provides a measure of the current "length" of the transaction, is used to determine which transaction is to be restarted in case of a conflict between transactions resulting in a wait depth exceeding the predetermined depth. L(T) may be the number of locks currently held by a transaction T, the maximum of the number of locks held by any incarnation of transaction T, including the current one, or the sum of the number of locks held by each incarnation of transaction T up to the current one. In a distributed transaction processing system, L(T) is based on time wherein each global transaction is assigned a starting time, and this starting time is included in the startup message for each subtransaction, so that the starting time of global transaction is locally known at any node executing one of its subtransactions.

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Date, "An Introduction to Database Systems vol. II", Addison-Wesley Publishing Co., 1983, pp. 83-100.
Lorin et al., "Operating Systems", Addison-Wesley Publishing Co., 1984, pp. 91-92.
"Encyclopedia of Computer Science and Engineering", Ralston et al.-Editors, Van Nostrand Reinhold Co., pp. 1532-1535.

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