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Showing posts from December, 2010

NHibernate performance issues #4: slow query compilation - named queries

NHibernate provides many approaches how to query the database:
HQL (Hibernate Query Language)Criteria Query APILinqNative SQLFirst three of these querying methods define the body of query in the other than native SQL. It implies that NHibernate must transform these queries into native SQL - according to given dialect, e.g. into native MS SQL query.

If you really want to develop all-times fast application the described process can present unpleasant behavior. How to avoid query compilation?

Compiled named queries

Its ridiculous but everyone met compiled (and named) query. If you have at least once browsed the log which NHibernate produced, you have had to meet similar set of lines:

2010-12-13 21:26:42,056 DEBUG [7] NHibernate.Loader.Entity.AbstractEntityLoader .ctor:0 Static select for entity eu.podval.NHibernatePerformanceIssues.Model.Library: SELECT library0_.Id as Id1_0_, library0_.version as version1_0_, library0_.Address as Address1_0_, library0_.Director as Director1_0_, library0_.N…

NHibernate performance issues #3: slow inserts (stateless session)

The whole series of NHibernate performance issues isn't about simple use-cases. If you develop small app, such as simple website, you don't need to care about performance. But if you design and develop huge application and once you have decided to use NHibernate you'll solve various sort of issue. For today the use-case is obvious: how to insert many entities into the database as fast as possible?

Why I'm taking about previous stuff? The are a lot of articles how the original NHibernate's purpose isn't to support batch operations, like inserts. Once you have decided to NHibernate, you have to solve this issue.

Slow insertion
The basic way how to insert mapped entity into database is:
SessionFactory.GetCurrentSession().Save(object);But what happen when I try to insert many entities? Lets say, I want to persist
1000 librarieseach library has 100 books = 100k of bookseach book has 5 rentals - there are 500k of rentals It's really slow! The insertion took exactly