This document discusses parameters for tuning the performance of WebLogic servers. It covers OS-level TCP parameters, JVM heap size and GC logging parameters, WebLogic server-level parameters like work managers, execute queues, and stuck threads, and JDBC and JMS pool parameters. It also provides an overview of different types of garbage collection in the HotSpot JVM.

1. Xavier Cosultants
Weblogic
Performance
Tuning
1.What Parameters to tune
1.1 OS level parameters to tune
Typically most error conditions are TCP tuning parameter related and are
caused by the operating system’s failure to release old sockets from a
close_wait call. Common errors are “connection refused”, “too many open
files” on the server-side, and “address in use: connect” on the client-side. In
most cases, these errors can be prevented by adjusting the TCP wait_time
value and the TCP queue size.

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/dev/tcp tcp_time_wait_interval
/dev/tcp tcp_conn_req_max_q
1.2 JVM level parameters to tune
-Xms & -Xmx parameters to the same value
Specify –XX:Permsize & -XX:MaxPermSize parameters
JVM Architecture
-XX:NewSize
-XX:MaxNewSize
-XX:SurvivorRatio
Total JVM Heap (Xms Xmx) = Young + Tenured(also called Old)
Young = Eden + From (SS1) + To (SS2)
Many people configure the JVM Object Heap size with the total JVM size. The
Heap size does not include permgen space.
So,
JVM size = Object Heap size ( Xmx) + PermGen size ( -XX:PermGen –
XX:MaxPermGen
1.2.1 How to Enable GC log for JVM
SUN JDK
JAVA_OPTIONS="${JAVA_OPTIONS} -XX:+HeapDumpOnOutOfMemoryError
-verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -Xloggc:${LOGDIR}/gc.log"
JROCKIT
JAVA_OPTIONS="$JAVA_OPTIONS -DDebugSecurityAtn=true -DDebugSSL=true
-Xverbose:memory -Xverboselog:${LOGDIR}/gc.lo
EDEN ( Young Gen) S2 PermGem
-XX:PermGen
-XX:MaxPermGen
S1
Tenured ( Old Gen)

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Keep the server in “Production Mode” ( in production mode the parameters of the
weblogic servers are configured for highest performance)
1.3 Server level parameters to tune
1.3.1 Workmanagers
Each workmanager will have three parameters
a) Request Class
a. ResponseTime Request Class
b. FairShare Request Class
c. Context Request Class
b) Min. Thread Constraint
c) Max Thread Constraint
d) Capacity Constraint
Advantages of WM:
Allows each application to have its own workmanager. We can efficiently
allocate the worked threads as per the requirements of the application.
For eg. A heavy application will be assigned a work manger with high no. of
threads and a light application can be assigned a light workmanager.
1.3.2 Execute queues
Execute Queues were available in the old version of weblogic. ( 8.1)
From 9.2 onwards WorkManagers were introduced.
Execute Queues have a pool of threads associated with him, and all the incoming
requests to one weblogic JVM will land to default execute queue.
1.3.2 Difference between Work Managers & Execute Queues
Work managers provide you the ability to better control thread utilization (server performance)
than execute-queues, primarily due to the many ways that you can specify scheduling guidelines
for the priority-based thread pool. These scheduling guidelines can be set either as numeric values
or as the capacity of a server-managed resource, like a JDBC connection pool.
Number of Available Socket Readers

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1.3.3 Struck Threads
A stuck thread is a thread that cannot complete its current work or accept new work because of an
unfinished work or a deadlock.
WebLogic Server automatically detects when a thread in an execute queue becomes “stuck.”
StruckThreadMaxTime
1.3.4 Tuning Muxer
SocketReaders are nothing but Muxer Threads.
SOCKET READERS – threads  these threads use software packages. These ‘software
packages” are called Muxers.
So, a socket reader using a software package called “muxer” is called a muxer thread.
Muxers are “software
The socket Muxer manages the server’s existing socket connections. It first determines
which sockets have incoming requests waiting to be processed. It then reads enough data
to determine the protocol and dispatches the socket to an appropriate runtime layer based
on the protocol. In the runtime layer, the socket muxer threads determine which execute
thread queue to be used and delegates the request accordingly.
Backlog buffering
The Accept Backlog parameter specifies how many
Transmission Control Protocol (TCP) connections can be buffered in a wait queue
JDBC level parameters to tune
Pool size - keep the optimal value for “initial capacity” , max capacity &
capacity increment.
TestConnectionsOnReserve – checks the connections before giving to
application. It minimizes the possibility of delivering an invalid connection to the
application.
JMS level parameters to tune

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Persistant store
Message size & Queue Size
Bridge
How to force garbage collection & threaddump from console
Servers  <server-name>  monitoring  performance.
A thread dump can also be taken using kill -3 <PID>
Theread dump will be stored in console log.
What are the Types of Garbage Collection
(For sun HOT SPOT JVM)

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Garbage collections are divided into 4 major types based on how the collection is done
in Young Generation & Old Generation.
For Each generation either SERIAL Or PARALLEL algorithms are used.
Both these Serial & Parallel algorithms are STOP-THE-WORLD algorithms. Which
means the application will come to stand still ( or stops ) when the GC is happening.
So what is the difference ?
SERIAL – stop-the-world & Uses single Thread
PARALLE – stop-the-world BUT uses Multiple Threads.
Even though PARALLEL GC stops the application, but because it is using multiple
threads ( enabled in multi cpu hardware) the GC time is less than a serial collector.
For this reason, PARALLEL GC is also called, through-put GC.
Apart from stop-the-world gc there is another GC , that doesn’t stop the application
completely but does it in small pauses. Its called Concurrent Mark Sweep GC.
TYPE OF GC Young
Generation
Old
Generatio
n
Remarks
SerialGC (-XX:+UseSerialGC) Serial Serial
Types of GC flow chart
STOP-THE-WORLD GC
SERIAL GC
-XX:+UseSerialGC
PARALLEL GC
-XX:+UseParallelGC
Concurrent Mark
Sweep GC (CMS)
:
+UseConcurrentMarkSweep
GC
PARALLEL COMPACTING
GC
-XX:+UseParallelOldGC

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ParallGC (-XX:+UseParallelGC) Parallel Serial
Parallel Compacting
(-XX:+UseParallelOldGC)
Parallel Parallel
Concurrent Mark Sweep GC
(-XX:+UseConcMarkSweepGC)
Parallel CMS So from above table,
+UseParallelOldGC
& CMS can not be
used together.
+XX:-UseParallelNewGC can be used with –XX:+UseConcMarkSweepGC
Sample Output of GC:
What to Look for in GC logs..
• Occurrences of garbage collections that were initiated by CICS when the
heap utilization threshold was reached.
• Occurrences of garbage collections that were caused by an allocation failure.
• The amount of free space in the storage heap, in bytes and as a percentage.
For Version 1.4.2, the output shows only the amount of free space after a
garbage collection, but with Version 5, the amount of free space before a
garbage collection is also shown.
• The time taken for each garbage collection, in milliseconds.
• Occurrences of heap expansion.
• The amount by which a storage heap was expanded and the new size of the
heap, in bytes.