Inside Documentum

Momentum 2008 – XML Store

On Tuesday and Wednesday I attended a load more sessions covering XML Store, Centrestage, Composer, Sharepoint and Web Content Management. In the next few posts I’ll share some of my thoughts and impressions, starting with XML Store.

For those that don’t know, EMC purchased a company called X-hive a while back. X-hive have an XML database product and that has now been integrated into the full Content Server stack. The easiest way to picture this is to take the old picture of the repository as consisting of a relational database and a file system and add in a third element, the XML Store.

From 6.5 (possibly sp1, I don’t remember) all XML is stored in the XML store. The XML Store is built around the many XML standards that are in existence such as XQuery, XSL and the XML full-text query standard.

The XML is not stored in the usual textual XML format but in a DOM format. This presumably is to allow them to implement various types of index and to optimise the query access patterns. The performance claims for the database are impressive although they need to be taken with a pinch of salt. As with all benchmarking, vendors will target specific goals in the benchmark. However your real-life workloads could be very different. If you are expecting high-throughput for an application using the XML store I suggest you put some work into designing and executing your own benchmarks.

In addition to indexes there is also a caching facility. This was only talked about at a high-level, however just as relational database performance experts made a career in 1990s out of sizing the buffer cache properly so we may see something similar with XML database installations. We may see them suffering poor performance as a result of under-sized hardware and mis-configuration. As always don’t expect this to just work without a little effort and research.

One other point I should make is that the XML Store is not limited to the integrated Content Server implementation. You can also install instances of XML Store separately. For example the forthcoming Advanced Site Caching Servicees product provides for a WebXML target. This is essentially an XML Store database installed alongside the traditional file system target that you currently get with SCS. You can then use the published XML to drive all sorts of clever dynamic and interactive web sites.