After a burst, a connection pool holds a lot of open connections. How long do they stay? I opened 8, closed them, and counted them every minute: they go after about 3 minutes, down to Minimum Pool Size.

Maximum Pool Size defaults to 100, and MySQL's max_connections to 151. So two copies of an app can ask for more than the server allows, and more requests than the pool holds can end the whole process. Here's how I picked a number, from measurements.

Opening a MySQL connection takes many round trips: TCP, TLS, then signing in. So MySql.Data keeps connections open after you close them, and hands them out again. A few lines of C# let you watch it work, and see what it saves.

MySqlConnectionStringBuilder turns a MySQL connection string into named properties, in both directions. It writes a valid string whatever your password holds, and it reads one back, with every default filled in. That's handy for logging settings without the password.

A connection string is a list of name=value pairs, split by ;. So a ; in your password ends the value early, and the rest looks like a strange option. Here's every case I tested, and the way to avoid thinking about it.

MySQL 9.7 allows TLS 1.3, and .NET 10 supports it, yet MySql.Data connects with TLS 1.2. It's the driver's default, on every platform. One connection string option changes that, and macOS needs one more setting.

SslMode=VerifyFull is the strongest check MySql.Data has: it verifies who signed the server's certificate, and that it's for the host you're connecting to. With PEM files, the driver also demands a client certificate and key, in one exact format. I hit each requirement in turn, so here they all are.

SslMode=Required encrypts the connection, and doesn't check who's at the other end. VerifyCA adds that check: your app only connects to a server whose certificate was signed by a CA you trust. It takes one file, and two options.

SslMode in a MySql.Data connection string decides two things: whether the connection is encrypted, and whether the driver checks who's on the other end. Required, the one most examples show, does the first and not the second. I tested each mode to see what it really does.

SET PERSIST is easy to forget about, and then a setting keeps coming back after every restart. RESET PERSIST removes it, but with a catch that had me double-checking: it leaves the running value as it is.