SQLConnection Pooling - Handling InvalidOperationExceptions - sqlconnection

Question

I am designing a Highly Concurrent CCR Application in which it is imperative that I DO NOT Block or Send to sleep a Thread.
I am hitting SQLConnection Pool issues - Specifically getting InvalidOperationExceptions when trying to call SqlConnection.Open
I can potentially retry a hand full of times, but this isn't really solving the problem.
The ideal solution for me would be a method of periodically re-checking the connection for availablity that doesn't require a thread being tied up
Any ideas?
[Update]
Here is a related problem/solution posted at another forum
The solution requires a manually managed connection pool. I'd rather have a solution which is more dynamic i.e. kicks in when needed

Answer 1

Harry, I've run into this as well, also whilst using the CCR. My experience was that having completely decoupled my dispatcher threads from blocking on any I/O, I could consume and process work items much faster than the SqlConnection pool could cope with. Once the maximum-pool-limit was hit, I ran into the sort of errors you are seeing.
The simplest solution is to pre-allocate a number of non-pooled asynchronous SqlConnection objects and post them to some central Port<SqlConnection> object. Then whenever you need to execute a command, do so within an iterator with something like this:
public IEnumerator<ITask> Execute(SqlCommand someCmd)
{
// Assume that 'connPort' has been posted with some open
// connection objects.
try
{
// Wait for a connection to become available and assign
// it to the command.
yield return connPort.Receive(item => someCmd.Connection = item);
// Wait for the async command to complete.
var iarPort = new Port<IAsyncResult>();
var iar = someCmd.BeginExecuteNonQuery(iarPort.Post, null);
yield return iarPort.Receive();
// Process the response.
var rc = someCmd.EndExecuteNonQuery(iar);
// ...
}
finally
{
// Put the connection back in the 'connPort' pool
// when we're done.
if (someCmd.Connection != null)
connPort.Post(someCmd.Connection);
}
}
The nice thing about using the Ccr is that it is trivial to add the following the features to this basic piece of code.
Timeout - just make the initial receive (for an available connection), a 'Choice' with a timeout port.
Adjust the pool size dynamically. To increase the size of the pool, just post a new open SqlConnection to 'connPort'. To decrease the size of the pool, yield a receive on the connPort, and then close the received connection and throw it away.

Answer 2

Yes, connections are kept open and out of the connection pool. In the above example, the port is the pool.