ERROR 2006 (HY000): MySQL server has gone away No

 個人問題是參數max_allowed_packet=4M過小致使，同過在my.cnf裏添加max_allowed_packet=16M重啓mysql服務器生效，下面文件設置mysql> set global max_allowed_packet=1024*1024*16;重啓後不生效。

（都忘記當時啥情況了）

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

 

緣由1. MySQL 服務宕了

判斷是否屬於這個緣由的方法很簡單，執行如下命令，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)

或者查看MySQL的報錯日誌，看看有沒有重啓的信息

$ 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)

若是uptime數值很大，代表mysql服務運行了好久了。說明最近服務沒有重啓過。

若是日誌沒有相關信息，也表名mysql服務最近沒有重啓過，能夠繼續檢查下面幾項內容。

2. 鏈接超時

若是程序使用的是長鏈接，則這種狀況的可能性會比較大。

即，某個長鏈接好久沒有新的請求發起，達到了server端的timeout，被server強行關閉。

此後再經過這個connection發起查詢的時候，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

這種狀況和狀況2類似，只是發起者是DBA或者其餘job。發現有長時間的慢查詢執行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.

當查詢的結果集超過 max_allowed_packet 也會出現這樣的報錯。定位方法是打出相關報錯的語句。

用select * into outfile 的方式導出到文件，查看文件大小是否超過 max_allowed_packet ，若是超過則須要調整參數，或者優化語句。

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：

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)