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Recovery Protocol Using a Common Log

IP.com Disclosure Number: IPCOM000049442D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Homas, P: AUTHOR [+3]

Abstract

This invention relates to a method for minimizing synchronous writing to a shared log among concurrent referencing nodes (tasks) while preserving independence of node (task) leading order of the log. The nodes (tasks) communicate, using a two-phase COMMIT/ABORT protocol. The method steps include (1) recording by the two-phase COMMIT coordinator in the shared log of the dependent node identities as a function of information type, and recording by the slave nodes of the coordinator identity; and (2) in the event of system failure during two-phase COMMIT resynchronizing the system states by way of the coordinator and dependent nodes.

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Recovery Protocol Using a Common Log

This invention relates to a method for minimizing synchronous writing to a shared log among concurrent referencing nodes (tasks) while preserving independence of node (task) leading order of the log. The nodes (tasks) communicate, using a two-phase COMMIT/ABORT protocol. The method steps include (1) recording by the two-phase COMMIT coordinator in the shared log of the dependent node identities as a function of information type, and recording by the slave nodes of the coordinator identity; and (2) in the event of system failure during two-phase COMMIT resynchronizing the system states by way of the coordinator and dependent nodes.

More particularly, the invention relates to a recovery protocol for a transaction processing system composed of a set of resource managers for disk joint recoverable resources plus a transaction manager. In order to ensure recoverability for committed transactions, a recovery log containing resource manager recovery records plus the "COMMIT" record must be written into non-volatile storage before transaction completion can be reported to the user. When multiple resource managers are involved in a single transaction, a two-phase COMMIT protocol, controlled by the transaction manager, must be employed to ensure that each resource manager will be able to restore its part of the transaction. Under this method, resource managers employ a fixed logging protocol, using a common log, in order to record the information necessary to either recover or remove the effects of the transaction from their recoverable resource state.

If a common log is not used, then each resource manager must synchronously write its own log at least once and the transaction manager must synchronousely write his log two times. Using a common log, only a single synchronous log write is required. The method is implementable by way of logging rules for resource managers and for the transaction manager, restart rules for reading the log for resource managers and for the transaction, and a synchronization rule for determining the transaction status given the resource manager status and the transaction manager status. It is desirable that the resource and transaction managers each maintain a scoreboar...