MySQL Server has gone away报错原因汇总分析

July 18, 2014

背景：在平时和开发的交流 以及 在论坛回答问题的或称中会发现这个问题被问及的频率非常高。 程序中报错： MySQL server has gone away 是什么意思？ 如何避免？ 因此，感觉有必要总结一下发生这个问题的原因。今天正好看到一篇外文blog总结的比较好，就翻译过来了

原因1. MySQL 服务宕了
---------------

判断是否属于这个原因的方法很简单，执行以下命令，查看mysql的运行时长

```
    $ tail /var/log/mysql/error.log
    130101 22:22:30 InnoDB: Initializing buffer pool, size = 256.0M
    130101 22:22:30 InnoDB: Completed initialization of buffer pool
    130101 22:22:30 InnoDB: highest supported file format is Barracuda.
    130101 22:22:30 InnoDB: 1.1.8 started; log sequence number 63444325509
    130101 22:22:30 [Note] Server hostname (bind-address): '127.0.0.1'; port: 3306
    130101 22:22:30 [Note]   - '127.0.0.1' resolves to '127.0.0.1';
    130101 22:22:30 [Note] Server socket created on IP: '127.0.0.1'.
    130101 22:22:30 [Note] Event Scheduler: Loaded 0 events
    130101 22:22:30 [Note] /usr/sbin/mysqld: ready for connections.
    Version: '5.5.28-cll'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL)
    ```

如果uptime数值很大，表明mysql服务运行了很久了。说明最近服务没有重启过。 如果日志没有相关信息，也说明mysql服务最近没有重启过，可以继续检查下面几项内容。

原因2. 连接超时
---------

如果程序使用的是长连接，则这种情况的可能性会比较大。 即，某个长连接很久没有新的请求发起，达到了server端的timeout，被server强行关闭。 此后再通过这个connection发起查询的时候，就会报错server has gone away

```
    $ mysql -uroot -p -e "show global variables like '%timeout';"
    +----------------------------+----------+
    | Variable_name              | Value    |
    +----------------------------+----------+
    | connect_timeout            | 30       |
    | delayed_insert_timeout     | 300      |
    | innodb_lock_wait_timeout   | 50       |
    | innodb_rollback_on_timeout | OFF      |
    | interactive_timeout        | 28800    |
    | lock_wait_timeout          | 31536000 |
    | net_read_timeout           | 30       |
    | net_write_timeout          | 60       |
    | slave_net_timeout          | 3600     |
    | wait_timeout               | 28800    |
    +----------------------------+----------+
    mysql> SET SESSION wait_timeout=5;
    
    
    # Wait 10 seconds
    
    mysql> SELECT NOW();
    ERROR 2006 (HY000): MySQL server has gone away
    No connection. Trying to reconnect...
    Connection id:    132361
    Current database: *** NONE ***
    
    +---------------------+
    | NOW()               |
    +---------------------+
    | 2013-01-02 11:31:15 |
    +---------------------+
    1 row in set (0.00 sec)
    ```

原因3. 进程在server端被主动kill
----------------------

这种情况和情况2相似，只是发起者是DBA或者其他job。发现有长时间的慢查询执行kill xxx导致。

```
    $ mysql -uroot -p -e "show global status like 'com_kill'"
    +---------------+-------+
    | Variable_name | Value |
    +---------------+-------+
    | Com_kill      | 0     |
    +---------------+-------+
    ```

原因4. Your SQL statement was too large.
--------------------------------------

当查询的结果集超过 max_allowed_packet 也会出现这样的报错。定位方法是打出相关报错的语句。 用select * into outfile 的方式导出到文件，查看文件大小是否超过 max_allowed_packet ，如果超过则需要调整参数，或者优化语句。

```
    mysql> show global variables like 'max_allowed_packet';
    +--------------------+---------+
    | Variable_name      | Value   |
    +--------------------+---------+
    | max_allowed_packet | 1048576 |
    +--------------------+---------+
    1 row in set (0.00 sec)
    
    # 修改参数：
    
    mysql> set global max_allowed_packet=1024*1024*16;
    mysql> show global variables like 'max_allowed_packet';
    +--------------------+----------+
    | Variable_name      | Value    |
    +--------------------+----------+
    | max_allowed_packet | 16777216 |
    +--------------------+----------+
    1 row in set (0.00 sec)
    ```

原文：[http://ronaldbradford.com/blog/sqlstatehy000-general-error-2006-mysql-server-has-gone-away-2013-01-02/][1]

[1]: http://ronaldbradford.com/blog/sqlstatehy000-general-error-2006-mysql-server-has-gone-away-2013-01-02/

添加新评论