Algorithms for flexible space management in transaction systems supporting fine-granularity locking

Abstract

We present several methods which relate to space management in a transaction system supporting fine-granularity (e.g., record) locking. These methods enable varying length records to be supported efficiently by permitting garbage collection to be performed within a page without the moved records having to be locked or the movements having to be logged. We present methods to do the following: (1) When a transaction releases space, efficiently prevent that space from being consumed by other transactions until that transaction terminates, while allowing the same transaction to reuse the space it freed. (2) Under the correct circumstances, avoid reading a totally empty deallocated page from disk during page reallocation. (3) Updating and logging of free space inventory pages' (FSIPs') changes for correct recovery. (4) Reduce locking during a table scan by a transaction using the isolation level of cursor stability. Our methods improve concurrency and space utilization, and provide I/O and CPU savings. Our space reservation and FSIP logging methods have been implemented in DB2 V3 in preparation for DB2's support of record locking.