MySQL server has gone away報錯原因分析及解決辦法

緣由1. MySQL 服務宕了 

判斷是不是屬于這個緣由的方法很簡單，履行以下命令，查看mysql的運行時長 

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

或查看MySQL的報錯日志，看看有無重啟的信息 

$ 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數(shù)值很大，表明mysql服務運行了很久了。說明最近服務沒有重啟過。 

如果日志沒有相干信息，也表名mysql服務最近沒有重啟過，可以繼續(xù)檢查下面幾項內(nèi)容。 

2. 連接超時 

如果程序使用的是長連接，則這類情況的可能性會比較大。 

即，某個長連接很久沒有新的要求發(fā)起，到達了server真?zhèn)€timeout，被server強行關(guān)閉。 

爾后再通過這個connection發(fā)起查詢的時候，就會報錯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) 

3. 進程在server端被主動kill 

這類情況和情況2相似，只是發(fā)起者是DBA或其他job。發(fā)現(xiàn)有長時間的慢查詢履行kill xxx致使。 

$ mysql -uroot -p -e "show global status like 'com_kill'" 
+---------------+-------+ 
| Variable_name | Value | 
+---------------+-------+ 
| Com_kill | 0 | 
+---------------+-------+ 
4. Your SQL statement was too large. 

當查詢的結(jié)果集超過 max_allowed_packet 也會出現(xiàn)這樣的報錯。定位方法是打出相干報錯的語句。 

用select * into outfile 的方式導出到文件，查看文件大小是不是超過 max_allowed_packet ，如果超過則需要調(diào)劑參數(shù)，或優(yōu)化語句。 

mysql> show global variables like 'max_allowed_packet'; 
+--------------------+---------+ 
| Variable_name | Value | 
+--------------------+---------+ 
| max_allowed_packet | 1048576 | 
+--------------------+---------+ 
1 row in set (0.00 sec) 
修改參數(shù)： 

mysql> set global max_allowed_packet=1024*1024*16; 
mysql> show global variables like 'max_allowed_packet'; 
+--------------------+----------+ 
| Variable_name | Value | 
+--------------------+----------+ 
| max_allowed_packet | 16777216 | 
+--------------------+----------+ 

參考： http://www.lai18.com/content/319554.html

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