请耐心看完全部
情况1. MySQL服务宕机
执行以下命令,查看mysql的运行时长。
mysql> show global status like 'uptime'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | Uptime | 10170 | +---------------+-------+
uptime数值很大,表明mysql服务运行很久,说明最近MySQL服务器没有重启过。
或者查看MySQL的报错日志,看看有没有重启的信息。
datou:~$ tail /var/log/mysql/error.log 170914 19:44:37 InnoDB: Completed initialization of buffer pool 170914 19:44:37 InnoDB: highest supported file format is Barracuda. 170914 19:44:37 InnoDB: Waiting for the background threads to start 170914 19:44:38 InnoDB: 5.5.57 started; log sequence number 58681764 170914 19:44:38 [Note] Server hostname (bind-address): '127.0.0.1'; port: 3306 170914 19:44:38 [Note] - '127.0.0.1' resolves to '127.0.0.1'; 170914 19:44:38 [Note] Server socket created on IP: '127.0.0.1'. 170914 19:44:38 [Note] Event Scheduler: Loaded 0 events 170914 19:44:38 [Note] /usr/sbin/mysqld: ready for connections. Version: '5.5.57-0ubuntu0.14.04.1' socket: '/var/run/mysqld/mysqld.sock' port: 3306 (Ubuntu)
如果日志没有相关信息,也表明mysql服务最近没有重启过,可以继续检查下面几项情况。
情况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> show global variables like '%timeout'; +----------------------------+----------+ | Variable_name | Value | +----------------------------+----------+ | connect_timeout | 10 | | 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 | +----------------------------+----------+ 10 rows in set (0.00 sec)
如下命令设置连接超时为5秒。
mysql> SET SESSION wait_timeout=5;
Query OK, 0 rows affected (0.00 sec)
再执行SELECT NOW();
,通过这个connection发起查询的时候,就会报错server has gone away。
mysql> SELECT NOW(); ERROR 2006 (HY000): MySQL server has gone away No connection. Trying to reconnect... Connection id: 41 Current database: study +---------------------+ | NOW() | +---------------------+ | 2017-09-14 23:12:53 | +---------------------+ 1 row in set (0.01 sec)
实际上wait_timeout=28800,不是造成文章开头的原因。
情况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> show global status like 'com_kill'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | Com_kill | 0 | +---------------+-------+ 1 row in set (0.00 sec)
情况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。
查看执行SQL执行文件大小是否超过 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 | 16777216 | +--------------------+----------+ 1 row in set (0.00 sec)
计算发现SQL执行文件最大只能是16M,而文章开头执行的a.sql有24M。
修改参数,max_allowed_packet 调整为28M。
mysql> set global max_allowed_packet=1024*1024*28; Query OK, 0 rows affected (0.00 sec) mysql> show global variables like 'max_allowed_packet'; +--------------------+----------+ | Variable_name | Value | +--------------------+----------+ | max_allowed_packet | 29360128 | +--------------------+----------+ 1 row in set (0.00 sec)
1. 修改 连接MySQL的php文件
增加 PDO::ATTR_PERSISTENT => false, PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true,
如下:
$PDO = @new PDO("mysql:host=$DB_HOST;dbname=$DB_NAME","$DB_USER","$DB_PASSWORD", array(PDO::ATTR_PERSISTENT => false, PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true, PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8';"));
2.修改 php.ini
vim /etc/php.ini
mysqli.reconnect = Off
修改成:
mysqli.reconnect = On
3.修改 程序,增加检测
注意此处使用的是mysqli的扩展,非mysql扩展
function ping(){ if(!mysqli_ping($this->link)){ mysqli_close($this->link); //注意:一定要先执行数据库关闭,这是关键 $this->connect(); } }
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