Re: Connector/J "Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost."

[Dean Jiang]

I encountered another problem which seems the same.

Platform: CentOS 5.0
I connect to mysql whose wait_timeout is set to 10 seconds.
Every 15 seconds, I execute a simple query, then exception goes up:

{{{
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 1 ms ago.
at sun.reflect.GeneratedConstructorAccessor4.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3009)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2895)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3438)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1951)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2548)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2477)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1422)
at my.Jdbc.executeOne(Jdbc.java:55)
at my.Jdbc.main(Jdbc.java:18)
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2455)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2906)
... 9 more

}}}

then I close the connection with Connection.close(), establish a new connection with DriverManager.getConnection().
Interesting things appear, I check the fds with " ll /proc/<pid>/fd " and found lots of socket still open!
{{{
lrwx------ 1 root root 64 Jul 9 16:56 50 -> socket:[8250228]
lrwx------ 1 root root 64 Jul 9 16:56 51 -> socket:[8249645]
lrwx------ 1 root root 64 Jul 9 16:56 52 -> socket:[8250236]
lrwx------ 1 root root 64 Jul 9 16:56 54 -> socket:[8250292]
lrwx------ 1 root root 64 Jul 9 16:56 55 -> socket:[8249789]
lrwx------ 1 root root 64 Jul 9 16:56 56 -> socket:[8250201]
....and more....
}}}
every time the "Communications link failure" occurs, the fd count increases by 1.

I'm really shocked :(
Does anyone know why?