参考:
https://blog.csdn.net/weixin_34293141/article/details/93057113
https://blog.csdn.net/qq_40236927/article/details/106525281
https://blog.csdn.net/weixin_44374545/article/details/123272886
https://www.jianshu.com/p/3a397a358a22
https://zhuanlan.zhihu.com/p/94279621
同事反馈公司的一个java客户端工具运行异常，后台log如下：
2022-12-08 10:52:28 WARN BasicResourcePool:223 - com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@18afde8 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
java.sql.SQLException: null, message from server: "Host 'VBJVDI00378.test.com' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1095)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2031)
at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:718)
at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:46)
at sun.reflect.GeneratedConstructorAccessor6.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
log重点：
2022-12-08 10:52:28 WARN BasicResourcePool:223 - com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@18afde8 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
java.sql.SQLException: null, message from server: "Host 'VBJVDI00378.test.com' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
根据重点log，可以找到以下几点：
1）问题：
Host 'VBJVDI00378.test.com' is blocked because of many connection errors
同一个ip在短时间连接MySQL服务失败次数超过max_connection_errors参数设定值(默认10)，MySQL则认为是数据库出错，并且阻止了站点的链接。
2）解决方法一：
unblock with 'mysqladmin flush-hosts
终端中执行mysqladmin -uroot -p -h localhost flush-hosts
或者连接数据库后执行flush hosts
mysql>flush hosts
3）解决方法二：
进入数据库将max_connection_errors参数调高，或者修改my.cnf（需要重启MySQL）。
mysql>show variables like '%max_connection_errors%';
mysql>set global max_connect_errors = 1000;
mysql>show variables like '%max_connection_errors%';
注意：配置有master/slave主从数据库的要把主库和从库都修改一遍的。
