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Asked: 2026-05-11T12:14:42+00:00

I use NHibernate in my ASP.NET application to connect to an MS SQL Server

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I use NHibernate in my ASP.NET application to connect to an MS SQL Server 2005 database. In some cases I need to write my own SQL queries. However, I noticed that the SQL server thread leaks about 50 KB of memory every time I execute the following piece of code:

NHibernate.ISession session = NHibernateSessionManager.Instance.GetSession();  ISQLQuery query = session.CreateSQLQuery(   'select {a.*} from t_alarm a where a.deactivationtime > '' +   DateTime.UtcNow.ToString('yyyy-MM-dd HH:mm:ss') +   ''');  query.AddEntity('a', typeof(TAlarm)); System.Collections.IList aList = query.List();

When I look in Windows task manager I see that the process sqlservr.exe increases its memory usage by 50 KB each time I run this code.

Here is the really interesting part. If I, in the code above, replace 'yyyy-MM-dd HH:mm:ss' with 'yyyy-MM-dd HH:mm' (i.e. I remove the seconds) the memory leaks stop.

Update: Apparently the memory leaks doesn’t actually stop. They just show once a minute instead. Presumably when the SQL query changes.

The returned results are the same in both cases.

Does anyone have a clue what is going on here?

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1 Answer

  1. a) In the example you are not properly disposing NHibernate’s Session, so the connection to DB is left opened.

    Use using() {} statemenet or try{} cath{} finally{} to properly close connection.

    b) SQL command you have written do not use SQL parameters, so SQL server will see this as a new command every time you execute it – more precisely every second (or if you remove :ss part, then every minute). Use SQL parameters (like NHibernate do when you use HQL, Criteria or QBE quering) and it will be cached properly with less memory consumption.

    Hope this helps;)

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