Many Of the Times when there is a Server Crash, We take a Thread
dump and analyze the threads running. During that time we see many threads like
these
"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" id=20 idx=0x68 tid=26709 prio=5 alive,
in native, blocked, daemon
-- Blocked trying to
get lock: java/lang/String@0x2b673d373c50[fat lock]
at
jrockit/vm/Threads.waitForUnblockSignal()V(Native Method)
at
jrockit/vm/Locks.fatLockBlockOrSpin(Locks.java:1675)[optimized]
at
jrockit/vm/Locks.lockFat(Locks.java:1776)[optimized]
at
jrockit/vm/Locks.monitorEnterSecondStageHard(Locks.java:1312)[optimized]
at
jrockit/vm/Locks.monitorEnterSecondStage(Locks.java:1259)[optimized]
at
jrockit/vm/Locks.monitorEnter(Locks.java:2439)[optimized]
at
weblogic/socket/EPollSocketMuxer.processSockets(EPollSocketMuxer.java:153)
at
weblogic/socket/SocketReaderRequest.run(SocketReaderRequest.java:29)
at
weblogic/socket/SocketReaderRequest.execute(SocketReaderRequest.java:42)
at
weblogic/kernel/ExecuteThread.execute(ExecuteThread.java:145)
at weblogic/kernel/ExecuteThread.run(ExecuteThread.java:117)
at
jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
These are called “Muxer Threads”. These
are the Special Threads in Web logic Server to read incoming request from
external entities on the servers. The main usage is to read the incoming request
and then pass them to either “execute Thread” or “work Manager”.
Weblogic allocates a percentage of the
Thread pool for these pools.The default value is 33% and not more than 50%.
We can assign the value using –Dweblogic.SocketReader=<Value>
Socket Muxer Threads
The Socket Muxer (SM) Threads are threads
that manage the existing Server socket connections.
It first checks the sockets and find
which socket has an incoming request which needs to be processed ( waiting to
be processed).Then It reads data like protocol and then it dispatches the
socket that to the run time layer which will process that.
In the run time layer, the SM will
identify the Execute Queue that needs to be used for the Socket.
There are 2 types of SM Threads In
Weblogic
Native SM & Java SM
Native SM [need to “enable Native I/O” in
Weblogic console]: Native SM provides better performance scalability since they
use the non blocking thread model. When Native I/O is used the server creates a
fixed number of threads especially for reading the incoming socket requests.
Java SM: This uses pure java
based threads. These are only available muxer for RMI clients. This is not a
suitable one since they blocks on read until there is a data to be read from
socket. This can cause bottleneck to the Server.
How can we find which SM is
being used?
When we check the Thread
Dump,if we see
NTSocketMuxer : Native SM
Weblogic.Socket.Muxer : Java SM
Weblogic.Socket.Muxer : Java SM
