Pushing XML Main Memory Databases to their Limits

The wide distribution of XML documents and the standardization of the Query languages XPath and XQuery have led to a wide variation of XML database implementations. Yet the efficient processing of really large XML documents is still supported by just a few products such as e.g. MonetDB/XQuery as open-source solution [1] or X-Hive as commercial product [2]. Following the main memory and relational encoding approach of MonetDB/XQuery, we analyse how far we can push main memory approaches to yield usable real-time query results for XPath requests. Moreover, we apply memory efficient value indexes to reach an order-ofmagnitude performance improvement for queries with predicate tests. The results of our implementation prototype are quite promising, surpassing the response times of any other implementation we tried so far.