There is a remote Mysql database. When running a php application, I sent a message that the MySQL server has gone away. I checked the Internet and most of the answers are as follows. Wait_timeout mysql defaults to 8 hours, so I didn't move. For that parameter, after changing max_allowed_packet to 16M (original only 1M), there is no connection loss phenomenon. Considering that mysql on the original server is used as the database of a java application, connect lost often occurs. I don't know if it is the same reason.
In the past two days, it was found that the java application still lost mysql connection frequently, because the mysql server was created on a virtual machine, the allocated memory at that time was only 4G, and the CPU was relatively slow.
[DEBUG]_2016-04-04 14:45:37 :com.mchange.v2.c3p0.impl.NewPooledConnection@152bf998 handling a throwable.
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 170,289 milliseconds ago. The last packet sent successfully to the server was 1 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1117)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3567)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3456)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3997)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2468)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2629)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2719)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1379)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.execute(NewProxyPreparedStatement.java:368)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3017)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3467)
... 157 more
This problem has troubled me for a long time, and there are many online settings about connect_timeout, interactive_timeout, wait_timeout that do not work
Accidentally show variables to see |net_read_timeout|30|
|net_write_timeout|30|These two parameters,
in /etc/my.cnf
net_read_timeout = 120
net_write_timeout = 120
Take a longer look at the settings and set net_read_timeout, net_write_timeout to 120.
The result is effective, and the Communications link failure has not occurred after running for a long time .
mysql> show variables like '%time%';
+---------------------------------+-------------------+
| Variable_name | Value |
+---------------------------------+-------------------+
| binlog_max_flush_queue_time | 0 |
| connect_timeout | 300 |
| datetime_format | %Y-%m-%d %H:%i:%s |
| delayed_insert_timeout | 300 |
| explicit_defaults_for_timestamp | OFF |
| flush_time | 0 |
| innodb_flush_log_at_timeout | 1 |
| innodb_lock_wait_timeout | 50 |
| innodb_old_blocks_time | 1000 |
| innodb_rollback_on_timeout | OFF |
| interactive_timeout | 28800 |
| lc_time_names | en_US |
| lock_wait_timeout | 31536000 |
| long_query_time | 10.000000 |
| net_read_timeout | 120 |
| net_write_timeout | 120 |
| rpl_stop_slave_timeout | 31536000 |
| slave_net_timeout | 3600 |
| slow_launch_time | 2 |
| system_time_zone | CST |
| time_format | %H:%i:%s |
| time_zone | SYSTEM |
| timed_mutexes | OFF |
| timestamp | 1459753718.898598 |
| wait_timeout | 28800 |
+---------------------------------+-------------------+
25 rows in set (0.00 sec)
Consider whether it is actually the cause of the server's performance and network instability,
slave-net-timeout
The number of seconds to wait for more data from the master before the slave considers the connection broken, aborts the read, and tries to reconnect. The first retry occurs immediately after the timeout. The interval between retries is controlled by the MASTER_CONNECT_RETRY option for the CHANGE MASTER TO statement, and the number of reconnection attempts is limited by the --master-retry-count option. The default is 3600 seconds (one hour).
当slave认为连接master的连接有问题时，就等待N秒，然后断开连接，重新连接master
net_read_timeout ：
The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort
在终止读之前，从一个连接获得数据而等待的时间秒数；当服务正在从客户端读取数据时，net_read_timeout控制何时超时。
net_write_timeout:
The number of seconds to wait for a block to be written to a connection before aborting the write.When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort。
在终止写之前，等待多少秒把block写到连接；当服务正在写数据到客户端时，net_write_timeout控制何时超时
wait_timeout
The number of seconds the server waits for activity on a noninteractive connection before closing it.
与服务器端无交互状态的连接，直到被服务器端强制关闭而等待的时间
interactive_timeout ：
The number of seconds the server waits for activity on an interactive connection before closing it.
与服务器端无交互状态的连接，直到被服务器端强制关闭而等待的时间
connect_timeout
The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.
等待一个连接响应的时间
connect_timeout：在获取连接阶段（authenticate）起作用
interactive_timeout和wait_timeout：在连接空闲阶段（sleep）起作用
net_read_timeout和net_write_timeout：则是在连接繁忙阶段（query）起作用。
获取MySQL连接是多次握手的结果，除了用户名和密码的匹配校验外，还有IP->HOST->DNS->IP验证，任何一步都可能因为网络问题导致线程阻塞。为了防止线程浪费在不必要的校验等待上，超过connect_timeout的连接请求将会被拒绝。
即使没有网络问题，也不能允许客户端一直占用连接。对于保持sleep状态超过了wait_timeout（或interactive_timeout，取决于client_interactive标志）的客户端，MySQL会主动断开连接。
即使连接没有处于sleep状态，即客户端忙于计算或者存储数据，MySQL也选择了有条件的等待。在数据包的分发过程中，客户端可能来不及响应（发送、接收、或者处理数据包太慢）。为了保证连接不被浪费在无尽的等待中，MySQL也会选择有条件（net_read_timeout和net_write_timeout）地主动断开连接。