What does this mean? Why is it happening?

Question

MySQL

[20.10.19 19:49:25] L2DatabaseFactory: Failed to retrieve database connection!
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
  at sun.reflect.GeneratedConstructorAccessor73.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:425)
  at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)
  at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342)
  at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2188)
  at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2221)
  at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2016)
  at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776)
  at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
  at sun.reflect.GeneratedConstructorAccessor71.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:425)
  at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386)
  at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
  at org.apache.commons.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
  at org.apache.commons.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582)
  at org.apache.commons.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:1148)
  at org.apache.commons.dbcp.AbandonedObjectPool.borrowObject(AbandonedObjectPool.java:79)
  at org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:106)
  at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
  at ru.catssoftware.L2DatabaseFactory.getConnection(L2DatabaseFactory.java:128)
  at ru.catssoftware.gameserver.util.QueuedItems$1.run(QueuedItems.java:76)
  at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.ConnectException: Connection refused (Connection refused)
  at java.net.PlainSocketImpl.socketConnect(Native Method)
  at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
  at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
  at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
  at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
  at java.net.Socket.connect(Socket.java:589)
  at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)
  at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301)
  ... 20 more

Something with the MYSQL database seems to disappear
mainly in the evenings, almost every day.

2019-10-22T03:06:59.940805Z 4807 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:00.178937Z 4807 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:01.732520Z 4808 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:04.860964Z 4808 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:05.380610Z 4809 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:05.627374Z 4809 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:07.143244Z 4810 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:07.379718Z 4810 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:09.072248Z 4811 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:09.317083Z 4811 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:10.291268Z 4812 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:13.500931Z 4812 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:14.058111Z 4813 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:14.302534Z 4813 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:14.841044Z 4814 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:15.077352Z 4814 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:07:15.602896Z 4815 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Temporary failure in name resolution
2019-10-22T03:07:15.850999Z 4815 [Note] Access denied for user 'root'@'XXX.XX.XX.XX' (using password: YES)
2019-10-22T03:10:21.237410Z 4823 [Note] Got an error reading communication packets
2019-10-22T08:53:17.063622Z 5557 [Warning] IP address 'XXX.XX.XX.XX' has been resolved to the host name '25.XXX.XX.XXX.adsl-pool.jlccptt.net.cn', which resembles IPv4-address itself.
2019-10-22T08:53:17.066028Z 5557 [Note] Got an error reading communication packets
2019-10-22T11:10:25.623969Z 4825 [Note] Aborted connection 4825 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got timeout reading communication packets)
2019-10-22T11:10:30.923995Z 4827 [Note] Aborted connection 4827 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got timeout reading communication packets)
2019-10-22T11:10:31.371982Z 4828 [Note] Aborted connection 4828 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got timeout reading communication packets)
2019-10-22T12:41:25.518742Z 6044 [Warning] IP address 'XXX.XX.XX.XX' could not be resolved: Name or service not known
2019-10-22T12:41:35.528593Z 6044 [Note] Got timeout reading communication packets
2019-10-22T15:58:14.193809Z 6493 [Warning] Host name '34-128.XXX.XXX.serverhubrdns.in-addr.arpa' could not be resolved: Name or service not known
2019-10-22T15:58:24.202019Z 6493 [Note] Got timeout reading communication packets
2019-10-22T17:19:46.322993Z 6374 [Note] Aborted connection 6374 to db: 'NAMEBASE' user: 'NAME' host: '109.196.134.84' (Got timeout reading communication packets)
2019-10-22T19:28:51.800131Z 6993 [Note] Aborted connection 6993 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got an error reading communication packets)
2019-10-22T19:28:51.800204Z 6966 [Note] Aborted connection 6966 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got an error reading communication packets)
2019-10-22T19:28:51.800338Z 6994 [Note] Aborted connection 6994 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got an error reading communication packets)
2019-10-22T19:28:51.800888Z 6918 [Note] Aborted connection 6918 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got an error reading communication packets)
2019-10-22T19:29:05.708578Z 7006 [Note] Got an error reading communication packets
2019-10-22T19:29:08.848003Z 7009 [Note] Aborted connection 7009 to db: 'NAMEBASE' user: 'NAME' host: 'localhost' (Got an error reading communication packets)
2019-10-22T19:29:21.836540Z 7013 [Note] Got an error reading communication packets
2019-10-22T19:51:06.036879Z 7086 [Note] Got an error reading communication packets

many IPs unknown to me.

Answer 1

https://ru.stackoverflow.com/questions/932363/andr...
I hope this helps.

Answer 2

From the client side
The client cannot connect to the database.
From the database side
Feeling like the database can't access DNS, check DNS operation during problems.
here is the whole article
https://www.percona.com/blog/2016/05/16/mysql-got-...