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);
SqlDataReader dr = cmd.ExecuteReader();
//process the result
There is a good MSDN blog article about this (a little old but the principle is the same) which has more info.
Artemakis Artemiou is a Senior SQL Server Architect, Author, Software Developer and a Microsoft Data Platform MVP. He has over 15 years of experience in the IT industry in various roles. Among other, via his initiative SQLEBooks.com, Artemakis authors and publishes eBooks on different topics 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). Additionally he is the founder of the SQLArtBits initiative that aims to provide the technical community with simple, yet powerful and high-quality SQL Server tools. Currently, the highlights of these tools are DBA Security Advisor and In-Memory OLTP Simulator. Artemakis's official website can be found at aartemiou.com. Artemakis's blogs can be found at: SQLNetHub.com and TechHowTos.com.