How to force a SqlConnection to physically close, while using connection pooling?

Question

I understand that if I instantiate a SqlConnection object, I am really grabbing a connection from a connection pool. When I call Open(), it will open the connection. If I call the Close() or Dispose() method on that SqlConnection object, it is returned to the connection pool.

However, that doesn't really tell me if it's really closed, or if I still have an active connection to the database.

How can I force a SqlConnection to close at the network level, or at least tell when it closes?

Example:

using(SqlConnection conn = new SqlConnection(DBConnString)) {     conn.Open();    SqlCommand cmd = conn.CreateCommand();    ...    cmd.ExecuteReader(CommandBehavior.CloseConnection);    ... } 

• First run: 300 ms
• Second run: 100 ms
• Third run: 100 ms
• After waiting a long time (30 minutes): 300 ms

If the connection was TRULY closing, the second and third runs should also be 300 ms. But I know that the connection is not truly closed for those runs (I checked the SQL Server's activity monitor). It doesn't take the extra 200ms to perform authentication/etc.

How do I force the connection to truly close?

Ideas

• Does CommandBehavior.CloseConnection work? (apparently not?)
• Does setting "Max Pool Size = 0" in the connection string work? (this would be a pyrrhic solution)
• Does Dispose() work?

References

• Article on Connection Pooling
• Here's another one that tells us that Close() doesn't really close the connection.
• An article on pros and cons connection pooling

Answer 1

Maybe SqlConnection.ClearPool ?

Answer 2

Moe Sisko's answer (Call SqlConnection.ClearPool) is correct.

Sometimes you need a connection to really close rather than return to the pool. As an example, I have a unit test that creates a scratch database, builds the schema, tests some stuff, then drops the scratch database if the tests all pass.

When connection pooling is active, the drop database command fails because there are still active connections. From the point of view of programmer all SQLConnections are closed, but as the pool still holds one open, SQL Server won't allow the drop.

The best documentation for how connection pooling is handled is this page on SQL Server Connection Pooling on MSDN. One doesn't want to turn connection pooling off entirely because it improves performance with repeated opens and closes, but sometimes you need to call a "force close" on an SQLConnection so that it will let go of the database.

This is done with ClearPool. If you call SqlConnection.ClearPool(connection) before closing/disposing, when you do close/dispose it will really go away.