This was a scary error message I got it today while I tried to switch my EF project to connect to a live database. The way I did the switch was have a pair of Entity Framework connection strings in my web.config, with one pointing to development and one to production database, and when the switch turned to production, the system will automatically pick up the live connection string; and that’s it. Test had been going well in development environment and the production database was exact copy, in terms of schema, of the developmental one, so I felt confident to make the switch and expected the codes should run as expected.

But then came this ugly and convoluted error message from the bottom of Entity framework, “Adding the specified count to the semaphore would cause it to exceed its maximum count.”; what on the earth was this? Google search for the phrase returned quite a few answers, some suggesting it might be sql queries had error, other pointing to Microsoft internal bug in db connection pooling. I found this one clicked – disabling pooling; I always favor simple than complex; this was simplest to do, just added an entry to my connection string, which by default was enabling connection pooling. Amazingly, that did it and the error went away! So here was the EF connection string before I made the change, connectionString=”metadata=res://*/MyModel.csdl|res://*/MyModel.ssdl|res://*/MyModel.msl;provider=System.Data.SqlClient;provider connection string="data source=sqlSvr1;initial catalog=sqlDb1;integrated security=false;user id=user1;password=password1234!;multipleactiveresultsets=True;App=EntityFramework"”

and here is the connection string that cleared the semaphore error,  connectionString=”metadata=res://*/MyModel.csdl|res://*/MyModel.ssdl|res://*/MyModel.msl;provider=System.Data.SqlClient;provider connection string="data source=sqlSvr1;initial catalog=sqlDb1;integrated security=false;user id=user1;password=password1234!;pooling=false;multipleactiveresultsets=True;App=EntityFramework"”

More interestingly, after the error went away, I took out the pooling=false, and ran the app again, things just flied without anymore problem; I also switched back to development database, with pooling option enabled, and still didn’t see the semaphore error as I expected that I would. So, if I could regenerate the error at some point, I suspect if I just simply clean the solution and rebuild the entire solution, I might achieve the same outcome – no more this dreadful and convoluted error, “Adding the specified count to the semaphore would cause it to exceed its maximum count.” (got it from the InnerException)