The last few days we see this error message in our website too much:
"Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached."
We have not changed anything in our code in a while. I revised the code to check open connections which didn't close, but found everything to be fine.
How can I solve this?
Do I need to edit this pool?
How can I edit this pool's max number of connections?
What is the recommended value for a high traffic website?
Do I need to edit something in IIS?
I found that the number of active connections are anywhere from 15 to 31, and I found that the max allowed number of connections configured in SQL server is more than 3200 connections, is 31 too many or should I edit something in the ASP.NET configration?
In most cases connection pooling problems are related to connection leaks. Your application probably doesn't close its database connections correctly and consistently. When you leave connections open, they remain blocked until the .NET garbage collector closes them for you by calling their
You want to make sure that you are really closing the connection. For example the following code will cause a connection leak, if the code between
Close throws an exception:
var connection = new SqlConnection(connectionString);
// some code
The correct way would be this:
var connection = new SqlConnection(ConnectionString);
using (SqlConnection connection = new SqlConnection(connectionString))
When your function returns a connection from a class method make sure you cache it locally and call its
Close method. You'll leak a connection using this code for example:
var command = new OleDbCommand(someUpdateQuery, getConnection());
result = command.ExecuteNonQuery();
The connection returned from the first call to
getConnection() is not being closed. Instead of closing your connection, this line creates a new one and tries to close it.
If you use
SqlDataReader or a
OleDbDataReader, close them. Even though closing the connection itself seems to do the trick, put in the extra effort to close your data reader objects explicitly when you use them.
This article "Why Does a Connection Pool Overflow?" from MSDN/SQL Magazine explains a lot of details and suggests some debugging strategies:
sp_who2. These system stored procedures return information from the
sysprocesses system table that shows the status of and information about all working processes. Generally, you'll see one server process ID (SPID) per connection. If you named your connection by using the Application Name argument in the connection string, your working connections will be easy to find.
TSQL_Replay template to trace open connections. If you're familiar with Profiler, this method is easier than polling by using sp_who.