Allow sessions with changed databases to be pooled. Fixes #515

Author: bgrainger

src/MySqlConnector/Core/ConnectionPool.cs

@@ -67,7 +67,7 @@ public async ValueTask<ServerSession> GetSessionAsync(MySqlConnection connection
 					}
 					else
 					{
-						if (ConnectionSettings.ConnectionReset)
+						if (ConnectionSettings.ConnectionReset || session.DatabaseOverride != null)
 						{
 							reuseSession = await session.TryResetConnectionAsync(ConnectionSettings, ioBehavior, cancellationToken).ConfigureAwait(false);
 						}
@@ -148,10 +148,8 @@ private bool SessionIsHealthy(ServerSession session)
 				return false;
 			if (session.PoolGeneration != m_generation)
 				return false;
-			if (session.DatabaseOverride != null)
-				return false;
 			if (ConnectionSettings.ConnectionLifeTime > 0
-			    && unchecked((uint) Environment.TickCount) - session.CreatedTicks >= ConnectionSettings.ConnectionLifeTime)
+				&& unchecked((uint) Environment.TickCount) - session.CreatedTicks >= ConnectionSettings.ConnectionLifeTime)
 				return false;
 
 			return true;

src/MySqlConnector/Core/ServerSession.cs

@@ -364,7 +364,7 @@ public async Task<bool> TryResetConnectionAsync(ConnectionSettings cs, IOBehavio
 
 			try
 			{
-				if (ServerVersion.Version.CompareTo(ServerVersions.SupportsResetConnection) >= 0)
+				if (DatabaseOverride == null && ServerVersion.Version.CompareTo(ServerVersions.SupportsResetConnection) >= 0)
 				{
 					m_logArguments[1] = ServerVersion.OriginalString;
 					Log.Debug("Session{0} ServerVersion={1} supports reset connection; sending reset connection request", m_logArguments);
@@ -380,8 +380,17 @@ public async Task<bool> TryResetConnectionAsync(ConnectionSettings cs, IOBehavio
 				else
 				{
 					// optimistically hash the password with the challenge from the initial handshake (supported by MariaDB; doesn't appear to be supported by MySQL)
-					m_logArguments[1] = ServerVersion.OriginalString;
-					Log.Debug("Session{0} ServerVersion={1} doesn't support reset connection; sending change user request", m_logArguments);
+					if (DatabaseOverride == null)
+					{
+						m_logArguments[1] = ServerVersion.OriginalString;
+						Log.Debug("Session{0} ServerVersion={1} doesn't support reset connection; sending change user request", m_logArguments);
+					}
+					else
+					{
+						m_logArguments[1] = DatabaseOverride;
+						Log.Debug("Session{0} sending change user request due to changed Database={1}", m_logArguments);
+						DatabaseOverride = null;
+					}
 					var hashedPassword = AuthenticationUtility.CreateAuthenticationResponse(AuthPluginData, 0, cs.Password);
 					using (var changeUserPayload = ChangeUserPayload.Create(cs.UserID, hashedPassword, cs.Database, m_supportsConnectionAttributes ? s_connectionAttributes : null))
 						await SendAsync(changeUserPayload, ioBehavior, cancellationToken).ConfigureAwait(false);