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0 Replies Latest reply: Sep 21, 2010 9:05 AM by 843798 RSS

JMX/getHostByAddr

843798 Newbie
Currently Being Moderated
I ran into an issue where I have a Java JMX service running on a Linux
host that is taking 23 seconds to establish a TCP connection with a
client. I took a thread dump (see below) and discovered that the time
is spent by java doing a reverse DNS look-up on the inbound connection
attempt. We have disabled the NSCD (Name Service Cache Daemon) on our
host so the DNS delay is understandable.

Question: Why does java even care about resolving the hostname? JMX
is built on top of TCP. TCP does not require DNS to establish
connectivity so why does Java insist on obtaining a hostname for the
client's IP on an inbound connection?

at java.net.Inet4AddressImpl.getHostByAddr(Native Method) ????

"Thread-5" prio=10 tid=0x00002aaacc084800 nid=0x74b5 runnable
[0x0000000042ed7000]
java.lang.Thread.State: RUNNABLE
at java.net.Inet4AddressImpl.getHostByAddr(Native Method)
at java.net.InetAddress$1.getHostByAddr(Unknown Source)
at java.net.InetAddress.getHostFromNameService(Unknown Source)
at java.net.InetAddress.getHostName(Unknown Source)
at java.net.InetAddress.getHostName(Unknown Source)
at
com.sun.jmx.remote.socket.SocketConnection.<init>(SocketConnection.java:
60)
at
com.sun.jmx.remote.socket.SocketConnectionServer.accept(SocketConnectionServer.java:
173)
at
com.sun.jmx.remote.generic.SynchroMessageConnectionServerImpl.accept(SynchroMessageConnectionServerImpl.java:
47)
at javax.management.remote.generic.GenericConnectorServer
$Receiver.run(GenericConnectorServer.java:334)