Performance Optimizations

Optimizing Queries

Here are some general tips for optimizing queries with NHibernate:

• Select only the properties you need; that is, avoid selecting the full entity when you don’t need it.
• Avoid loading an entity when you only need its key (use ISession.Load<T> instead of ISession.Get<T>).
• Use paging instead of retrieving all records at the same time; all querying APIs support it.
• Fetch at query time all the references and collections that you will need.
• Choose lazy and eager loading carefully, and choose an appropriate fetch mode. If you are certain that you need a child collection’s items each time you load a specific entity, mark this collection as not lazy and with fetch mode JOIN.
• Resort to SQL queries when performance is crucial.

Optimizing Making Changes

Consider this:

• Always use explicit transactions.
• Use executable HQL for bulk updates and deletes.
• Use batching and stateless sessions for insertions.
• Evict unneeded entities from the session.
• Mark entities that you never want to change as immutable so that the session does not waste time with them when tracking changes.
• Use explicit flushing and, when flushing, also clear the session or evict unneeded entities.
• In production, disable logging and statistics.