node js:在查询之前检查mysql连接

Question

我使用带有mysql的节点js,并希望避免应用程序在连接错误时崩溃.现在我使用这个:

function mysql_handleDisconnect() {
  mysql_connection = mysql.createConnection(mysql_config_obj); // Recreate the connection, since
                                                  // the old one cannot be reused.

  mysql_connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      mysql_handleDisconnect(); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  mysql_connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      mysql_handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
      throw err;                                  // server variable configures this)
    }
  });
}

 mysql_handleDisconnect(mysql_connection);

所以这是阻塞,因为如果连接关闭它会导致热循环.我的问题是,如果我每隔2秒添加一个setTimeout重新建立连接,当我用"mysql_connection.query"进行查询时,我可能会遇到致命错误( 'SELECT ...')".在这种情况下,应用程序崩溃.

所以我的问题是,如果在我进行查询之前有可能检查连接？

Answer 1

在做任何事情之前,尝试在每个微服务中使用以下代码:

 if(connection.state === 'disconnected'){
     return respond(null, { status: 'fail', message: 'server down'});
   }