Concurrency

Abstract

Both papers in this session were about enhancing pessimistic R/W schemes for concurrency control. In the first Andrea Skarra described extensions to a 2PL scheme to take advantage of the semantics of operations on index sets. Use of an extra locking mode offers potentially greater concurrency. The system had been implemented, but as yet there were no hard figures on the performance. In discussion a number of detailed suggestions were made: path expressions could be used to control the invocation order of operations (not considered); an optimistic strategy might be better suited to handling operation semantics (not practicable with the current server architecture, but certainly worth bearing in mind). Ron Morrison thought that most production systems handle indexes specially anyway, and that solid experimental evidence was needed before additional lock modes could be justified.