1.由于在测试环境中，应用程序的微服务个数不是很多，且每个服务的连接池初始化链接数为:50,上线后一部分微服务出现大量以下的错误:

com.alibaba.druid.pool.GetConnectionTimeoutException: wait millis 60000, active 0, maxActive 50, creating 0, createErrorCount 9913
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.getConnection(JobStoreSupport.java:778)
    at org.quartz.impl.jdbcjobstore.JobStoreTX.getNonManagedTXConnection(JobStoreTX.java:71)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.doCheckin(JobStoreSupport.java:3261)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$ClusterManager.manage(JobStoreSupport.java:3874)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport$ClusterManager.run(JobStoreSupport.java:3911)
Caused by: com.alibaba.druid.pool.GetConnectionTimeoutException: wait millis 60000, active 0, maxActive 50, creating 0, createErrorCount 9913
    at com.alibaba.druid.pool.DruidDataSource.getConnectionInternal(DruidDataSource.java:1599)
    at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:1326)
    at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:1306)
    at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:1296)
    at org.apache.dolphinscheduler.service.quartz.DruidConnectionProvider.getConnection(DruidConnectionProvider.java:39)
    at org.quartz.utils.DBConnectionManager.getConnection(DBConnectionManager.java:108)
    at org.quartz.impl.jdbcjobstore.JobStoreSupport.getConnection(JobStoreSupport.java:775)
    ... 4 common frames omitted
Caused by: java.sql.SQLException: Access denied for user 'xxx'@'127.0.0.1' (using password: YES)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:996)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3887)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3823)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:870)
    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1659)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1206)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2234)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2265)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2064)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.GeneratedConstructorAccessor57.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:395)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1578)
    at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1644)
    at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2570)
[ERROR] 2020-12-15 05:59:22.374 com.alibaba.druid.pool.DruidDataSource:[2572] - create connection SQLException, url: jdbc:mysql://127.0.0.1:3306/xxx?characterEncoding=UTF-8&allowMultiQueries=true, errorCode 1045, state 28000
java.sql.SQLException: Access denied for user 'xxx'@'127.0.0.1' (using password: YES)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:996)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3887)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3823)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:870)
    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1659)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1206)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2234)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2265)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2064)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.GeneratedConstructorAccessor57.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:395)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1578)
    at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1644)
    at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2570)

2.该种错误在百度搜索了大量的资料，各种方式都尝试过了，突然想起线上mysql数据库是新装上的，通过:show variables like '%max_connections%'; 查询，发现最大的链接数为151(默认)

3.项目上线后，微服务太多，每个微服务的初始连接池链接个数都是50

4.mysql默认最大链接数是151，很显然链接是肯定不够用，只能支持三个微服务

5.通过:set GLOBAL max_connections = 6000; 语句将mysql最大链接数改为6000，问题得到解决