Efficient Transaction Management for XML Documents
||Efficient Transaction Management for XML Documents
||T. Grabs, K. Böhm, H.-J. Schek
||Eleventh International Conference on Information and Knowledge Management (ACM CIKM 2002)McLean, VA, USA
||Institute of Information Systems, ETH Zurich
A common approach to storage and retrieval of XML documents
is to store them in a database, together with materialized
views on their content. The advantage over native
XML storage managers seems to be that transactions
and concurrency are for free, next to other benefits. But
a closer look and preliminary experiments reveal that this
results in poor performance of concurrent queries and updates.
The reason is that database lock contention hinders
parallelism unnecessarily. We therefore investigate concurrency
control at the semantic, i.e., XML level and describe a
respective transaction manager XMLTM. It features a new
locking protocol DGLOCK. It generalizes the protocol for
locking on directed acyclic graphs by adding simple predicate
locking on the content of elements, e.g., on their text.
Instead of using the original XML documents, we propose to
take advantage of an abstraction of the XML document collection
known as DataGuides. XMLTM allows to run XML
processing at the underlying database at low ANSI isolation
degrees and to release database locks early without sacrificing
correctness in this setting. We have built a complete
prototype system that is implemented on top of the XML
Extender for IBM DB2. Our evaluation shows that our approach
consistently yields performance improvements by an
order of magnitude. We stress that our approach can also
be implemented within a native XML storage manager, and
we expect even better performance.
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