[sql-server] Is it possible to set a timeout for an SQL query on Microsoft SQL server?

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?

I might suggest 2 things.

1) If your query takes a lot of time because it´s using several tables that might involve locks, a quite fast solution is to run your queries with the "NoLock" hint.

Simply add Select * from YourTable WITH (NOLOCK) in all your table references an that will prevent your query to block for concurrent transactions.

2) if you want to be sure that all of your queries runs in (let´s say) less than 5 seconds, then you could add what @talha proposed, that worked sweet for me

Just add at the top of your execution

SET LOCK_TIMEOUT 5000;   --5 seconds.

And that will cause that your query takes less than 5 or fail. Then you should catch the exception and rollback if needed.

Hope it helps.

In management studio you can set the timeout in seconds. menu Tools => Options set the field and then Ok

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You can set Execution time-out in seconds.

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.

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.

It sounds like more of an architectual issue, and any timeout/disconnect you can do would be more or less a band-aid. This has to be solved on SQL server side, by the way of read-only replica, transaction log shipping (to give you a read-only server to connect to), replication and such. Basically you give the DMZ sql server that heavy read can go to without killing stuff. This is very common. A well-designed SQL system won't be taken down by DDoS - that'd be like a car that dies if you step on the gas.

That said, if you are at the liberty to change the code, you could guesstimate if the query is too heavy and you could either reject or return only X rows in your stored procedure. If you are mated to some reporting tool and such and can't control the SELECT it generates, you could point it to a view and then do the safety valve in the view.

Also, if up-to-the-minute freshness isn't critical and you could compromise on that, like monthly sales data, then compiling a physical table of complex joins by job to avoid complex joins might do the trick - that way everything would be sub-second per query.

It entirely depends on what you are doing, but there is always a solution. Sometimes it takes extra coding to optimize it, sometimes it takes extra money to get you the secondary read-only DB, sometimes it needs time and attention in index tuning.

So it entirely depends, but I'd start with "what can I compromise? what can I change?" and go from there.

Humm! did you try LOCK_TIMEOUT
Note down what it was orginally before running the query
set it for your query
after running your query set it back to original value

SET LOCK_TIMEOUT 1800;  
SELECT @@LOCK_TIMEOUT AS [Lock Timeout];