Reduce allocations when executing a command.

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -45,6 +45,7 @@ public ServerSession(ConnectionPool? pool, int poolGeneration, int id)
 			Pool = pool;
 			PoolGeneration = poolGeneration;
 			HostName = "";
+			SingleCommandList = new IMySqlCommand[1];
 			m_logArguments = new object?[] { "{0}".FormatInvariant(Id), null };
 			Log.Debug("Session{0} created new session", m_logArguments);
 		}
@@ -65,6 +66,7 @@ public ServerSession(ConnectionPool? pool, int poolGeneration, int id)
 		public bool SupportsDeprecateEof => m_supportsDeprecateEof;
 		public bool SupportsSessionTrack => m_supportsSessionTrack;
 		public bool ProcAccessDenied { get; set; }
+		public IMySqlCommand[] SingleCommandList { get; }
 
 		public void ReturnToPool()
 		{

src/MySqlConnector/MySql.Data.MySqlClient/MySqlCommand.cs

@@ -267,7 +267,17 @@ internal async Task<DbDataReader> ExecuteReaderAsync(CommandBehavior behavior, I
 				throw exception;
 
 			m_commandBehavior = behavior;
-			return await CommandExecutor.ExecuteReaderAsync(new IMySqlCommand[] { this }, SingleCommandPayloadCreator.Instance, behavior, ioBehavior, cancellationToken).ConfigureAwait(false);
+			var commandList = m_connection!.Session.SingleCommandList;
+			var oldCommand = commandList[0];
+			try
+			{
+				commandList[0] = this;
+				return await CommandExecutor.ExecuteReaderAsync(commandList, SingleCommandPayloadCreator.Instance, behavior, ioBehavior, cancellationToken).ConfigureAwait(false);
+			}
+			finally
+			{
+				commandList[0] = oldCommand;
+			}
 		}
 
 		public MySqlCommand Clone() => new MySqlCommand(this);