The timeout period elapsed prior to obtaining a connection from the pool

The timeout period elapsed prior to obtaining a connection from the pool

If you are working with .NET applications, at some time you might get the below (or similar) error message:

Exception message: 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.

The most probable reason you are getting the above error message, is that your application
opens connection to the database without closing them. This situation is then repeated and after a number of times, the application throws an exception because it cannot open more than a given number (max pool) of connections to the database.

The best practice is to let .NET do the connection handling for you by running your SQL queries with the “using” statement. Here’s a C# example:
using (SqlConnection conn = new SqlConnection(connString))
   {
      SqlCommand cmd = new SqlCommand(“SELECT @@VERSION”, conn);
      conn.Open();      
      SqlDataReader dr = cmd.ExecuteReader();
      //process the result
      dr.Close();
   }
}
There is a good MSDN blog article about this (a little old but the principle is the same) which has more info.

The SQL Server and .NET Hub
Reference: The SQL Server and .NET Hub (http://www.sqlnethub.com)

Artemakis Artemiou
Artemakis Artemiou is a Senior SQL Server and Software Architect, Author, and a 9 Times Microsoft Data Platform MVP (2009-2018). He has over 15 years of experience in the IT industry in various roles. Artemakis is the founder of SQLNetHub and TechHowTos.com. Artemakis is the creator of the well-known software tools Snippets Generator and DBA Security Advisor. Also, he is the author of many eBooks on SQL Server. Artemakis currently serves as the President of the Cyprus .NET User Group (CDNUG) and the International .NET Association Country Leader for Cyprus (INETA). Artemakis's official website can be found at aartemiou.com.