有关mysql server has gone away报错的原因分析

发布时间:2020-01-17编辑:脚本学堂
有关mysql server has gone away报错的原因分析,供大家参考。程序中报错: MySQL server has gone away?这个应该如何避免呢?

有关mysql server has gone away报错的原因分析,供大家参考。
程序中报错: MySQL server has gone away?这个应该如何避免呢?

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:
 

复制代码 代码示例:
$ mysql -uroot -p -e "show global status like 'uptime';"
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Uptime        | 68928 |
+---------------+-------+
1 row in set (0.04 sec)

或者查看MySQL的报错日志,看看有没有重启的信息:
 

复制代码 代码示例:
$ 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,也表名mysql服务最近没有重启过,可以继续检查下面几项内容。

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
 

复制代码 代码示例:

$ 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)

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。
 

复制代码 代码示例:
$ mysql -uroot -p -e "show global status like 'com_kill'"
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Com_kill      | 0     |
+---------------+-------+

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。
 

复制代码 代码示例:
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:
 

复制代码 代码示例:
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)

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