Buffer fix procedure supporting both detection-based and avoidance-based cache coherency control scheme in a multisystem shared disk environment

摘要

PURPOSE: A buffer installation method is provided to select an optimal cache consistency maintenance policy between a detection and an avoidance based scheme by using a feature of the DBMS where a concurrency control is performed on a basis of the unit of a table, a block or a record. CONSTITUTION: The method comprises several steps. A buffer manager searches for a corresponding buffer entry in a buffer if a buffer installation is requested(S101). A buffer lock mode for processing a current request is calculated by using an SMTBM(Scheme Mode To Buffer lock mode Matrix)(S102). If the determined buffer lock mode is more enough rather than the buffer lock mode which a current buffer has already obtained, the buffer installation request is immediately approved(S108). But if the obtained lock mode is less than the requested buffer mode or a currently loaded block version does not satisfy a requested version(S103, S104), a buffer lock is requested to a global lock manager(S105), and the buffer lock is waited for until receiving a block is successful(S106). If the receiving the block is successful, the buffer installation is approved(S108) and otherwise, the block is read from a disc(S107).