Lesser-Known NHibernate Features: Statistics

NHibernate makes available a number of statistics about its work; this includes, among others:

• All of the queries executed;
• Number of entities loaded, inserted, updated and deleted;
• Number of optimistic concurrency misses;
• Number of second level cache hits and misses;
• Number of transactions started and committed;
• Number of connections opened and closed;
• etc.

This is available per session factory:

var statistics = sessionFactory.Statistics;

And all of these settings can be filtered per entity:

var entityStatistics = sessionFactory.Statistics.GetEntityStatistics("MyEntity");

Statistics can help us diagnose, for example, second level or query cache issues.

If we have no need for them, we can disable them before building the session factory:

cfg.SetProperty(NHibernate.Cfg.Environment.GenerateStatistics, Boolean.FalseString);

Or at runtime:

sessionFactory.Statistics.IsStatisticsEnabled = false;

An advice: do switch it off while on production, it does have an effect on performance.