Is it possible to set a timeout for an SQL query on Microsoft SQL server?

Question

I've got a scenario when sometimes a user selects the right parameters and makes a query which takes several minutes or more to execute. I cannot prevent him to select such a combination of parameters (it's quite legal), so I'd like to set a timeout on the query.

Note that I really want to stop the query execution itself and rollback any transactions, because otherwise it hogs up most of server resources. Add an impatient user who restarts the application and tries the combination again, and you've got a recipe for a disaster (read: sql server DoS).

Can this be done and how?

Answer 1

You can specify the connection timeout within the SQL connection string, when you connect to the database, like so:

"Data Source=localhost;Initial Catalog=database;Connect Timeout=15"

On the server level, use MSSQLMS to view the server properties, and on the Connections page you can specify the default query timeout.

I'm not quite sure that queries keep on running after the client connection has closed. Queries should not take that long either, MSSQL can handle large databases, I've worked with GB's of data on it before. Run a performance profile on the queries, prehaps some well-placed indexes could speed it up, or rewriting the query could too.

Update: According to this list, SQL timeouts happen when waiting for attention acknowledgement from server:

Suppose you execute a command, then the command times out. When this happens the SqlClient driver sends a special 8 byte packet to the server called an attention packet. This tells the server to stop executing the current command. When we send the attention packet, we have to wait for the attention acknowledgement from the server and this can in theory take a long time and time out. You can also send this packet by calling SqlCommand.Cancel on an asynchronous SqlCommand object. This one is a special case where we use a 5 second timeout. In most cases you will never hit this one, the server is usually very responsive to attention packets because these are handled very low in the network layer.

So it seems that after the client connection times out, a signal is sent to the server to cancel the running query too.

Answer 2

If you have just one query I don't know how to set timeout on T-SQL level.

However if you have a few queries (i.e. collecting data into temporary tables) inside stored procedure you can just control time of execution with GETDATE(), DATEDIFF() and a few INT variables storing time of execution of each part.

Answer 3

As far as I know, apart from setting the command or connection timeouts in the client, there is no way to change timeouts on a query by query basis in the server.

You can indeed change the default 600 seconds using sp_configure, but these are server scoped.