Is there any data on NHibernate vs Fluent NHibernate startup performance?

Question

In short, what works faster:

• SessionFactory precompiling XML configuration, or
• Fluent NHibernate providing configuration programmatically ?

Answer 1

My personal experience has been that the building of the Configuration object (which is unavoidable* regardless of whether Fluent is used) generally dwarfs the time required to setup a FluentConfiguration object, with the factor increasing as the number of mappings increase.

On a 2.5 Ghz c2d, with my project with approximately 15 mappings, it took 360ms for FluentConfiguration, and 5215ms for Configuration.

On a test project with 1000 mappings (simple classes with 2-3 string properties), it took 470ms for FluentConfiguration, and 40336 (40 seconds!) for Configuration.

_{*Actually, not really. most of the cost of Configuration comes from validating the XML mappings. Ayende has discussed it here (as well as a quick speedup obtained from merging the mappings into a single file), and a possible alternative to building the configuration at application startup is to serialize it as discussed here. In the 1000-mapping test project, this reduced the time required to get a Configuration object to around 30ms (although it has also increased the time required to build the SessionFactory from ~3 to ~4 seconds - I am unsure why).}