Implementing and Optimizing Fine-Granular Lock Management for XML Document Trees

Fine-grained lock protocols with lock modes and lock granules adjusted to the various XML processing models, allow for highly concurrent transaction processing on XML trees, but require locking facilities that efficiently support large and deep hierarchies with varying fan-out characteristics. We discuss these and also further requirements like prefix-based node labels, and present a lock management design that fulfills all these requirements and allows us to perfectly exploit the advantages of our tailor-made lock protocols for XML trees. Our design also supports the flexible use of heuristics for dynamic lock escalation to enhance workload adaptivity. Benchmark runs convincingly illustrate flexibility and performance benefits of this approach and reveal that careful lock protocol optimization pays off.