Use MySqlException.IsTransient

[bgrainger]

mysql-net/MySqlConnector#849 called for DbException.IsTransient to be implemented in MySqlConnector.

I ended up using the same list of error codes as Pomelo does:

• https://github.com/mysql-net/MySqlConnector/blob/396ad9d8d9aed29c6dc74e64e4678109ca306e51/src/MySqlConnector/MySqlException.cs#L130-L135

• Pomelo.EntityFrameworkCore.MySql/src/EFCore.MySql/Storage/Internal/MySqlTransientExceptionDetector.cs

  Lines 25 to 38 in 33b8d59

  	// Thrown if timer queue couldn't be cleared while reading sockets
  	case MySqlErrorCode.CommandTimeoutExpired:
  	// Unable to open connection
  	case MySqlErrorCode.UnableToConnectToHost:
  	// Too many connections
  	case MySqlErrorCode.ConnectionCountError:
  	// Lock wait timeout exceeded; try restarting transaction
  	case MySqlErrorCode.LockWaitTimeout:
  	// Deadlock found when trying to get lock; try restarting transaction
  	case MySqlErrorCode.LockDeadlock:
  	// Transaction branch was rolled back: deadlock was detected
  	case MySqlErrorCode.XARBDeadlock:
  	// Retry in all cases above
  	return true;

Once MySqlConnector > 1.3.0-beta.1 ships (with this change), Pomelo could update its method to simply delegate to MySqlException.IsTransient. This would let Pomelo benefit from any additional errors MySqlConnector considers to be transient in future versions.

OTOH, if you want to remain in control of this logic and not be affected by unexpected changes in MySqlConnector's implementation, then I understand that and you can close this issue. 😀

[lauxjpn]

Thanks, we are using it from now on.

Not considering MySqlErrorCode.CommandTimeoutExpired as transient as described in mysql-net/MySqlConnector#940 makes sense.