mysql - 连接到 google Cloud SQL 时，AppEngine 中有时会发生通信链接故障错误

Question

我从 1 年开始就在 google App Engine 中发布了一个后端项目，一切看起来都很好，1 周前，在 Cloud SQL 中执行 JPA 选择查询时，这个异常有时(不总是)开始抛出日志，有时查询是刚刚成功返回结果:

Internal Exception: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 309,979 milliseconds ago. The last packet sent successfully to the server was 309,981 milliseconds ago.
Error Code: 0
Call: SELECT ID, created_time, CURRENCY, IP, NAME FROM country_table Query: ReadAllQuery(name="Country.findAll" referenceClass=Country sql="SELECT ID, created_time, CURRENCY, IP, NAME FROM country_table")

有时这个异常会阻止一些查询的执行:

The last packet successfully received from the server was 219,443 milliseconds ago. The last packet sent successfully to the server was 219,446 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:44) at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1117) at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3851) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2471) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2651) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2739) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2149) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2313) at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeSelect(DatabaseAccessor.java:1007) at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:642) at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:558) at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:2002) at org.eclipse.persistence.sessions.server.ServerSession.executeCall(ServerSession.java:570) at org.eclipse.persistence.sessions.server.ClientSession.executeCall(ClientSession.java:250)

Answer 1

这是因为MySQL关闭了连接。

可能 JPA 会自动重新连接到数据库。如果交易结果正确，您可以忽略此消息。

或者您可以在开发人员控制台上使用 interactive_timeout 和 wait_timeout 延长计时器直到连接关闭。这可以减少消息。