Ayende @ Rahien

It's a girl

Poor man’s guide to database optimization - by the Marquis de Sade

One of the more common problems that I see over and over again in many applications is that test databases are too fast. As I have shown, this can easily lead to really sever cases of chattiness with the database, and all while the developer is totally oblivious.

This is especially true when you develop against a local database with almost no data, and deploy to a network database with lots of data. SELECT N+1 is bad enough, but when N is in the hundreds or more, it gets bad. The main problem is that developers aren’t really aware of that. This don’t see the problem, or feel it. And while they could fix it if they caught it in time, trying to come back to an existing application and fix all the many places where they assumed database access is free is a daunting task.

Therefore, I have set out to solve the problem. Obviously it is a problem with the developers not paying attention, but how can we deal with that?

Well, you could buy the NHibernate Profiler, which is my official recommendation. Or, if you don’t feel like spending money on this, you can utilize the following interceptor. That will make the developers sit up and notice when they start talking to the database.

public class SlowDownDudeInterceptor : EmptyInterceptor
{
    public override SqlString OnPrepareStatement(SqlString sql)
    {
        return sql.Insert(0, "waitfor delay '0:0:0.5'" + Environment.NewLine);
    }
}

Don’t go to production with this!

Comments

Markus Zywitza
05/29/2009 08:36 PM by
Markus Zywitza

Just an idea: Wouldn't such a thing be a good idea to simulate load on the DB server?

Neil
05/29/2009 08:50 PM by
Neil

I always thought that each db call should make the workstation beep, or make a systray thingee blink. I never got around to implementing anything like that, though.

Dmitry
05/30/2009 12:18 AM by
Dmitry

I always output (and inspect) queries into the console/debug stream for database tests. It's fairly easy to do with any ORM that implements a unit-of-work pattern and with log4net.

Chris Missal
05/30/2009 06:27 AM by
Chris Missal

This is a really good idea, but why stop there, maybe we can speed it up by using:

"waitfor delay '-0:0:0.5'"

What do you think?? ;)

Sosh
06/18/2009 12:28 PM by
Sosh

@Dmitry,

Could you give a quick example of how you would do that with say NHibernate? Thanks

Dmitry
06/18/2009 07:28 PM by
Dmitry

@Sosh,

NHibernate is by far the easiest ORM to implement logging. For unit testing you just add the configuration property true into the Web.Config/App.config file.

If you want to configure log4net to log into event log, DB, etc, here is the link: nhforge.org/.../...et-for-use-with-nhibernate.aspx

Entity Framework was a different story. It required a provider wrapper that sits between the object context and the database provider.

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