DATE: Thursday, April 15, 2004
TIME: Noon - 1 pm
PLACE: Wean Hall 8220

David McWherter
Carnegie Mellon

The Case for Preemptive Lock Scheduling in OLTP Workloads

OLTP workloads are increasingly common in computer systems, such as e-commerce and inventory management. It is valuable to provide priority scheduling in these systems, to reduce the response time for the most important clients, e.g. the "big spenders." Two-phase locking, commonly used in DBMS, makes prioritization difficult, as transactions wait for locks held by others regardless of priority. Existing lock scheduling solutions, including non-preemptive priority inheritance and preemptive abort, have performance drawbacks for TPC-C type workloads.

We evaluate several existing preemptive and non-preemptive lock prioritization policies for TPC-C type workloads. We conclude that high-priority transactions benefit greatly under preemptive abort as compared with non-preemptive policies. The low-priority transactions, however, suffer excessively.We conduct a detailed statistical analysis, explaining the performance results observed.We propose and implement POW, a lock prioritization policy, that provides all of all the benefits of preemption, without its costs.

David is a 3rd year PhD student working under Mor Harchol-Balter and with Anastassia Ailamaki on database and schuling problems, particularly those hard ones involving concurrency control and data consistency. In his spare time he studies coffee and chocolate.

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