普元 EOS Platform 7.5 mysql数据库，业务系统自早上频繁宕机，无法使用，后台报错：problems with communicating with the database(com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception

【问题】

EOS Platform 7.5 mysql数据库，业务系统自早上频繁宕机，无法使用，后台报错，trace.log中的异常：

Last packet sent to the server was 1 ms ago.
 at com.primeton.ext.common.connection.datasource.C3P0DataSourceProvider$ConnectionProxy.initConnection(C3P0DataSourceProvider.java:270)
 at com.primeton.ext.common.connection.datasource.C3P0DataSourceProvider$ConnectionProxy.prepareStatement(C3P0DataSourceProvider.java:484)
 at com.primeton.ext.infra.connection.ConnectionWrapper.prepareStatement(ConnectionWrapper.java:353)
 at com.primeton.das.entity.impl.DASSessionImpl.countBySubQuery(DASSessionImpl.java:466)
 ... 65 more
Caused by: com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.io.EOFException
STACKTRACE:
java.io.EOFException
 at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1905)
 at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2351)
 at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2862)
 at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1571)
 at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1666)
 at com.mysql.jdbc.Connection.execSQL(Connection.java:2988)
 at com.mysql.jdbc.Connection.setAutoCommit(Connection.java:4913)
 at com.mchange.v2.c3p0.impl.NewProxyConnection.setAutoCommit(NewProxyConnection.java:756)
 ......
 ......
 at com.eos.foundation.database.Pagination.doQueryPageCond(Pagination.java:515)
 at com.eos.foundation.database.DatabaseExt.queryEntitiesByCriteriaEntityWithPage(DatabaseExt.java:441)
** END NESTED EXCEPTION **

【解答】

问题原因：分析了现场生成的Thread dump日志，问题原因是查询语句执行慢导致数据库支撑不了。用户发起的查询请求长时间不返回，导致应用服务器的执行线程池被耗光，无法接入新的请求。

解决办法：对数据库的业务表进行了优化，问题解决