Optimizing lock protocols for native XML processing

TL;DR: This paper sketches the prototype native XML database system called XML Transaction Coordinator (XTC) and specifies the operations for accessing and modifying stored documents and introduces four XML lock protocols of growing sophistication and complexity, which are based on a tree-structured DOM storage model.

Abstract: Processing XML documents in multi-user database management environments requires a suitable storage model, support of typical XML document processing (XDP) interfaces, and concurrency control mechanisms tailored to the XML data model. In this paper, we sketch our prototype native XML database system called XML Transaction Coordinator (XTC) and specify the operations for accessing and modifying stored documents. The key contribution is the design and optimization of fine-grained lock protocols supporting collaborative processing of XML documents. For this reason, we introduce four XML lock protocols of growing sophistication and complexity, which are based on a tree-structured DOM storage model. The lock modes of these protocols, called taDOM* lock protocols, are tailor-made for the operations of the DOM API. Because of the protocols' complexity, their correctness is not obvious; hence, we present the ideas to prove the lock protocol correctness guaranteeing the specified data processing behavior of the given XDP operations. Finally, using XTC as our testbed system, we run extensive performance measurements to empirically evaluate our lock protocols and to compare their performance behavior against all known fine-grained competitor protocols under the same benchmark in an identical system setting. It turns out that tailor-made optimization pays off and that the taDOM* protocols are the clear winners in our lock protocol contest.