Efficient destaging of updated local cache pages for a transaction in a

Abstract

An efficient procedure for determining the set of buffer pool database pages that must be externalized to stable storage and for scheduling their write I/O's before release of a committing transaction's locks. In a multisystem database management system (DBMS) with high-speed shared external storage (SES) environment, a DBMS instance may follow 'force-at-commit' protocol for a database that has intersystem read/write interest or may alternatively follow a 'no-force-at-commit' policy when operating with a database for which only one system has interest. By introducing the concept of a series of unique ordinal numbers (ORD#) for each database assigned to buffer pool data pages whenever the page state changes from clean to dirty within a single DBMS instance, this procedure maintains a transaction page list (TPL) for each transaction in ORD# order. Because the dirty page list (DPL) pages are queued in ORD# sequence and each TPL includes all modified pages associated with the transaction, a merge scan with DPL entries can be performed for each TPL at the commit time of the corresponding transaction. This searches the DPL in a single pass with minimal DPL latch contention. The TPL pages requiring destaging are distributed to two processing lists; a first list for immediate force to SES and a second list of 'in-use' pages that are forced to SES if necessary upon release of existing process latches.