Optimizing Concurrency Through Automated Lock Memory Tuning in DB2

Lock memory consumption can be difficult to project and can vary rapidly in short amounts of time. This volatility makes lock memory tuning difficult and can result in either significant memory waste if systems are configured for peak requirements, or lock escalation and lock wait if under configured; either of which can cause significant performance penalties. This paper describes an algorithm for adaptive tuning of database lock memory. The DB2 technique adapts the locking memory in real time to mitigate the occurrence of lock escalations. The technique uses a combination of synchronous and asynchronous modification to the locking structures so that it can respond well to rapid immediate growth in locking requirements. The adaptive algorithm also relaxes the locking memory over time so that peak requirements in lock memory will not result in a permanently large allocation of memory to locks. Experimental tests have shown this technique to work well in a number of benchmark and adaptive workloads, converging almost immediately to optimal settings which avoid lock escalations and achieve optimal throughput. The solution has been implemented in DB2 9.