FOCCX: An Optimistic Concurrency Control Protocol over XML

Abstract

XML concurrency control protocol (CCP) is used to guard the consistence and isolation of transactions in Native XML databases. Experiments show that locking overhead of existing approaches based on locking may be huge, especially in the applications with few or without conflicts. Optimistic concurrency control (OCC) is an alternative to locking. This paper presents a new optimistic approach for concurrency control over XML documents named FOCCX (Forward oriented Optimistic Concurrency Control over XML) facing XPath-based API. FOCCX increases the degree of transaction concurrency. This is achieved by aborting the current transaction when a potential UPDATE-UPDATE conflict taking place as early as possible, and reduces comparison times by checking a small write set against read set of a limited number of concurrent transactions. Experimental results show that our protocol has superior performance to approaches based on Backward Oriented mechanism (BOCC).