Giving NHibernate a serious performance boost

March 8, 2006 · 1 min read

When NHibernate prepares SQL queries for SQL Server, it passes them to sp_execsql.  Upon first call, the query speed is lackluster as it parses and executes the SQL; on subsequent calls with the same query syntax, the speed gets a bit faster.  But even on subsequent calls, the response time is much slower than that of a stored procedure.  The problem is, by default, NHibernate does not fully qualify table names within its queries sent to SQL Server.  To leverage sp_execsql to its fullest, requests must include fully qualified table names.

You can fully qualify NHibernate queries within your app/web.config by including the following attribute in the nhibernate settings:

(Obviously, “dbo“ should also be replaced as necessary.)

How big of a difference does this make?  We're realizing an order of magnitude difference in the execution speed of queries called subsequent times.  A test query originally costing 255 reads went down to 12 reads.  On more data intensive pages, this can result in an overall performance gain of 33% or more.

(A big thanks out to Pete Weissbrod for researching this!)

This article is part of the GWB Archives. Original Author: Billy McCafferty

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