Sunday, 17 May 2009

Weblogic - Socket Muxers in Thread Dumps

What are these weblogic.socket.Muxer threads seen in thread dumps ?

Note: for a basic primer on taking thread dumps and analyzing them, see this earlier article

Socket Reader Threads accept the incoming request from the Listen Thread Queue and put it on the Execute Thread Queue.

In WL 8.1, there are 3 socket reader threads by default.
In WL 9 and 10, WebLogic allocates 33% of server threads to act as socket readers by default. This need not be changed usually.

One socket reader thread is usually in the poll function, while the others are available to process requests.
The polling thread is highlighted in the thread dump below.


"ExecuteThread: '2' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x016b2148 nid=0x42 waiting for monitor entry [5997f000..5997fc28]
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:91)
- waiting to lock <0x94846b40> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)


"ExecuteThread: '1' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x00683c28 nid=0x41 waiting for monitor entry [59a7f000..59a7fc28]
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:91)
- waiting to lock <0x94846b40> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)


"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x0079e5b0 nid=0x40 runnable [59b7f000..59b7fc28]
at weblogic.socket.PosixSocketMuxer.poll(Native Method)
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:100)
- locked <0x94846b40> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)



In an earlier support case on Stuck Threads, we asked BEA:

Should we worry about the Weblogic.socket.Muxer threads which always show 2 threads waiting for lock and 3rd thread locking the same object?

The Muxer TD is attached. This shows same behaviour on all our Weblogic servers.


Full thread dump Java HotSpot(TM) Server VM (1.4.2_05-b04 mixed mode):

"ExecuteThread: '2' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x0151
c588 nid=0x1b4 waiting for monitor entry [ad57f000..ad57fc28]
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:91)
- waiting to lock <0xd9331760> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)



"ExecuteThread: '1' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x0161
d608 nid=0x1b3 runnable [ad67f000..ad67fc28]
at weblogic.socket.PosixSocketMuxer.poll(Native Method)
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:100)
- locked <0xd9331760> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)



"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" daemon prio=5 tid=0x01bb
6730 nid=0x1b2 waiting for monitor entry [ad77f000..ad77fc28]
at weblogic.socket.PosixSocketMuxer.processSockets(PosixSocketMuxer.java:91)
- waiting to lock <0xd9331760> (a java.lang.String)
at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:32)
at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219)
at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)



The reply from BEA Support was that the above pattern of weblogic.socket.Muxer threads are not a cause of stuck threads.


Why do they mostly show as being Stuck in Samurai TD analyzer ?




As the image shows, when you analyze thread dumps using Samurai, the muxer threads are shown as being Stuck since they're all locked on the same object. This is probably treated as a deadlock condition.


"ExecuteThread: '2' for queue: 'weblogic.socket.Muxer'"
- waiting to lock <0xd9b61098> (a java.lang.String)


"ExecuteThread: '1' for queue: 'weblogic.socket.Muxer'"
- waiting to lock <0xd9b61098> (a java.lang.String)


"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'"
- locked <0xd9b61098> (a java.lang.String)



But you will see the same in any Thread dump even on a development instance with no requests.
The locks mentioned do show up as red in Samurai - but they aren't deadlocks just regular locks.

A thread gains an exclusive lock on an object to perform some action, then frees it allowing the next thread to gain access.

Additionally, if you look at the thread dumps over time, you'll see that these specific locks are not always present - they are moving between the threads which is indicative of their transitory nature.



I want to know more details on Muxers


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.

From the documentation on http://edocs.bea.com/wls/docs100/perform/WLSTuning.html#wp1152246 ,
Weblogic has two versions of the socket muxer, one is the Java version and the other uses a native library which makes better use of operating system calls. The Enable Native IO checkbox on the server’s configuration settings tells the server which version to use. This is ON by default for most platforms.

Native muxers provide superior scalability because they implement a non-blocking thread model. When a native muxer is used, the server creates a fixed number of threads dedicated to reading incoming requests. Oracle recommends using the default setting of true for the Enable Native IO parameter which allows the server to automatically select the appropriate muxer to use.

You must ensure that to use Native I/O, the native library must be present in the server’s shared library path . This is set up with the default scripts.
When the server does not find the native library, it throws an error
java.lang.UnsatisfiedLinkError: no muxer in java.library.path
and then loads the Java version of the muxer.

Confirm the LD library path is okay and pointing to the Solaris LD path. Check the startup log when starting a managed server. What is the value of java.library.path?
This is where the JVM actually get's the library from.

http://m-button.blogspot.com/2008/08/how-does-weblogic-handle-socket-muxers.html has a good example of how to identify Native vs Java muxer in a thread dump.

The Thread Dump I’ve used in my examples above uses the Native muxer (weblogic.socket.PosixSocketMuxer) on Solaris.

Solaris has another Native muxer called the weblogic.socket.DevPollSocketMuxer
An example TD using this muxer is shown below.


"ExecuteThread: '4' for queue: 'weblogic.socket.Muxer'" waiting for lock java.lang.String@4edf4f BLOCKED
weblogic.socket.DevPollSocketMuxer.processSockets(DevPollSocketMuxer.java:95)
weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)
weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)



"ExecuteThread: '3' for queue: 'weblogic.socket.Muxer'" RUNNABLE native
weblogic.socket.DevPollSocketMuxer.doPoll(Native Method)
weblogic.socket.DevPollSocketMuxer.processSockets(DevPollSocketMuxer.java:96)
weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)



weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)
"ExecuteThread: '2' for queue: 'weblogic.socket.Muxer'" waiting for lock java.lang.String@4edf4f BLOCKED
weblogic.socket.DevPollSocketMuxer.processSockets(DevPollSocketMuxer.java:95)
weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)
weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)



"ExecuteThread: '1' for queue: 'weblogic.socket.Muxer'" waiting for lock java.lang.String@4edf4f BLOCKED
weblogic.socket.DevPollSocketMuxer.processSockets(DevPollSocketMuxer.java:95)
weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)
weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)



"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" waiting for lock java.lang.String@4edf4f BLOCKED
weblogic.socket.DevPollSocketMuxer.processSockets(DevPollSocketMuxer.java:95)
weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)
weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)





To change the number of Muxers from the default, follow the instructions given at http://e-docs.bea.com/wls/docs92/ConsoleHelp/taskhelp/tuning/TuningSocketReaders.html




See http://jojovedder.blogspot.com/2009/07/more-on-weblogic-muxers.htmlfor an update on Muxers

Additionally on Oracle JRockit JVMs - there are some information in the thread dumps which point out the same problem in a different manner.

After the normal stack dumps, BEA JRockit performs a deadlock detection. This is done by finding "lock chains" in the Java application. If a lock chain is found to be circular, the application is considered caught in a deadlock.

A detailed explanation of the 3 types of lock chains in JRockit is given here


What is relevant for us is the example of Muxers which are shown as:


Blocked lock chains
===================
Chain 2:
"ExecuteThread: '2' for queue: 'weblogic.socket.Muxer'" id=129 idx=0x218 tid=4079 waiting for java/lang/String@0x37804000 held by:
"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" id=127 idx=0x210 tid=4077 in chain 1

Open lock chains
================
Chain 1:
"ExecuteThread: '1' for queue: 'weblogic.socket.Muxer'" id=128 idx=0x214 tid=4078 waiting for java/lang/String@0x37804000 held by:
"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" id=127 idx=0x210 tid=4077 (active)


As per the explanation, the Open lock chain depicts Thread 1 waiting for Thread 0. This is not a deadlock, only a straight dependency.

Since Thread 0 is already part of the Open lock chain, the fact that Thread 2 is also waiting on the same Thread 0 is treated as a "Blocked lock chain".
In this case this is not a problem.

Update 15th Feb 2011

I'm glad this blog entry on weblogic muxers has made it onto the Oracle forums with a mention from James Bayer.

Tuesday, 12 May 2009

Slow Server Response Part 4 - Platform Checks and Action Plan



In the earlier parts of this article I described some technical tuning tips specific to a slow-performing Weblogic JEE server.

Another earlier post has looked at analyzing thread dumps and prstats when the Weblogic/JEE server consumes high CPU.




This article provides a sequence of actions a Support team should carry out when faced with a critical situation - the site is down / servers running high CPU - and management teams want quick updates - and an action plan.

So here is (from experience) the Rapid Action Plan:


Technical Checklist for the Platform

1. Start a diary and mark out each of the steps given below as well as any following action with the timestamp at which it was carried out and the result/status.

2. Get the relevant technical experts on a conference call + Netmeeting/LiveMeeting/Desktop Sharing/Remote Admin.

3. Does the application have any traps or thresholds set which are configured to automatically raise alarms to the Support teams? Have any of the traps set been exceeded ? eg: Server CPU, Memory utilization, No of Threads

4. Can we narrow down to a problem area - Web server, Application server, Database, OS - based on log files, error messages and Support team or User input.

If a particular Weblogic Managed Server is identified as a point of failure, does the Configuration allow that server process to be shutdown for a while - thereby reducing Cluster capability but still providing acceptable Quality of service.

Are all the Managed Servers running with equal threads? If not, this can cause a load balancing issue.

Sometimes the bottleneck can be the Web server plugin which is not able to properly load balance the requests across the Weblogic cluster. This is usually the case when users complain of loss of session, spontaneous logout etc. The problem can be the user has been bounced from one Weblogic server to another in the cluster - and the session might not be replicated across the servers.

Any redundant JDBC connection pools - i.e. those configured with a high capacity but monitoring shows they dont need that many.
Then reduce the Capacity of that pool so that it does not hold on to unnecessary connections on the database.

5. From the log files, identify whether a particular application or code area is causing an issue. eg: EJB throwing errors, Spring bean configuration missing.

6. Are the log files too large (> 500 Mb) or not getting rotated via Weblogic rotation policy or Unix archiving ?

7. Check the Downstream Back-end systems which the server connects to - via DBLink, Web service, XML/Http, JMS, HTTP screen scraping etc.? Any known issues or planned outages? There should be error logs pointing in that direction. Contact their support teams to know if their system is available and returning responses as per the SLA.

8. Can the problem be replicated on Reference/Test instances?
A Dev or Test team can in parallel try out to see whether the issue is replicable.

If Yes, is it code related or configuration related?

If the issue is not replicable, then can it be data related ? Perhaps a particular set of data exists on Production which is not on the Test instance - and that could be the problem. Can the data be brought into Test to try and replicate the problem ?

9. Can it be content related? Does the platform have a Content Management System? Is the link from the CMS to the server working or broken? Is the Content correctly getting deployed into the database + file system as per daily process?

Check if there was a content deployment carried out and any records whether they failed or passed. Is content deployment happening during the business timings, and utilizing system and CPU resources - which chokes the JEE server?

Can a resource-hungry content deployment process be moved to out-of-business hours.

10. Test broken user journeys on the site.

Can the problem be seen while running HttpHeaders, HttpAnalyzer, Fiddler etc ? Does it show any change in HTTP parameters such as Cookies, Session timeouts?
Compare these against the Test environment and see whether any mismatches which could cause the problem.
If there is bouncing of user sessions between managed servers, this will be visible in the weblogic JSessionID which will be different on the client browser.

11. What were the last few changes to the platform ?

Check latest release or configuration change as per Support Team Diary of Events. Could these have caused an issue and should these be rolled back?

Were these properly tested and signed off before going into Production.

eg: any new Database driver, changes to TCP parameters, JTA timeouts increased?

12. Check the last few support cases raised? See if there were any problems reported by business or end customers.

13. Solaris/OS checks

Is the platform running on the latest OS patch levels and JDK settings as recommended by Sun.

a. No of processes running. Use
ps -ef | wc -l

b. Ping the boxes, to check if they are alive

c. CPU utilization

prstat

d. Memory utilization

vmstat 3

Swap space utilization, amount of space in /tmp - is there any old file or core dump occupying the directory used as swap space. We once moved old EAR files from /tmp on the server; memory utilisation went from approx 90% down to 65%.

e. Disk space

df -ek

f. No of File descriptors


14. Weblogic/Web server checks

a. Thread utilization - any Stuck Threads

Analyze Thread dumps , at least 4 sets of Thread dumps taken 5 seconds apart when stuck thread is observed. See here for more details on what to look for in the thread dumps. Use Samurai or TDA

b. CPU %

c. Access and error logs - Any CRITICAL messages in the logs. Any Connection_Refused errors indicating the threads were not able to accept new requests.

d. No of open sockets to weblogic

netstat -a | grep

e. Memory utilization via Weblogic console

f. Check via console if all the managed servers are up and running

g. Connection pool utilization, Are they hitting the peak values.

h. Frequent Garbage collection shown in the console?
Frequency of GC, GC pattern. Has the JVM been tuned to allow optimum garbage collection. See this URL for more.

i. Check for the values in weblogic.xml for jsp-pageCheckSeconds and servlet-reload-check-secs - if these are at the default of 1, the server will check each second to see whether the JSP should be recompiled - this is horribly slow

j. Cron job logs - any failures.

k. No of weblogic sessions per server - the more the number of HttpSessions, the higher the memory (RAM) that gets used.

l. Is a large part of the application journey over SSL. When supporting the cryptography operations in the SSL protocol, WebLogic Server cannot handle as many simultaneous connections.
Typically, for every SSL connection that the server can handle, it can handle three non-SSL connections. SSL reduces the capacity of the server by about 33-50% depending upon the strength of encryption used in the SSL connections.
(Source: http://edocs.bea.com/wlp/docs92/capacityplanning/capacityplanning.html#wp1080286)
Consider reducing the SSL journeys on the site.

m. Disk space taken by Weblogic and other logs such as Log4J.
Is log4j running in DEBUG and writing out loads of logs ? This will also slow down the server horribly.

15. Database checks

a. SQL Server locks (Call out DBA)

b. Database stuck/locked processes

c. Any DB link down

d. Any issues with open cursors, cached cursors ?

e. Is the database running at very high Memory Utilization?


16. Search Engine processing - check the log for the day.


17. Any MIS such as Webtrends / Omniture Analysis - for application usage. Has there been a sudden rise in users on the site - eg a marketing campaign or a new feature gone live - causing a rise in usage which the infrastructure cannot cope with.

18. Any application cached data which was wiped out and took time to rebuild - causing slow service in the interim period. eg: is any database table with a lot of rows being cached.
Or conversely, is there incorrect data in a certain cache and will clearing the cache help ?

19. SMTP email delivery failures due to any problems on the OS ?

20. Any planned backup processes running on the OS which takes up a lot of CPU.



Remedial actions

1. Make a list of possible changes based on the above checks to address these problems.

2. Only change one setting on any system at a time. Test and record the desired effects and observed effects. Be clear on why a particular change is being made.

3. If it doesn't work rework the plan to get to root cause of failure.

4. Be aware that reactive changes will be made directly to the production
environment by various parties. Significant changes will be made purely to enable investigation and diagnosis of issues.
The lack of up-to-date documentation creates risk. Maintain a documented rationale for a particular design decision, configuration choice, or system parameter; this reduces the likelihood that mistakes will be repeated. Documentation is a key communication tool, without it intent may be miscommunicated within the team. If key staff members leave, knowledge will be lost to the extent that the platform may become unmanageable.

5. Add additional tests to the regression test
suite. Increase the coverage of the regression test suite, focussing on
simulating live system interaction.


6. Over the long term, identify and re-architect towards removing Single Points of Failure - such that loss of a single machine or process would not lead to a loss of service.

Examples:
· Single web server machine, hosting the Apache/SunOne instances.
· Single application server machine, hosting the Weblogic application server.
· Single database server instance.

The system runs at risk of lengthy service outage if any one of these components fails. If a hardware failure occurred and one of the servers was lost, alternative hardware would need be installed and initialised from back-up tapes.
This needs to be fixed and stabilized over the long term.

6. While the analysis is going on, a member of Support team should circulate the KEY Metrics on an hourly basis to the TECHNICAL community. Ensure this is the important dataset and not too much info which just becomes noise.


Example in the table below:












Servers Server 1Server 2 Server 3
Idle Threads111417
JMSErrors1017
IOExceptions301
Stuck Threads007
JMSErrors1017
netstat -a | grep TIME_WAIT | wc -l 18628969
CPU Utilization (%)121.83.6
Memory Utilization (%)3.92.92.1
500 Internal Server Error300



No of logged in Users: 260

JMS Pending Messages: 0



Any queries or clarifications, leave me a comment and I'll try to get back.

Thursday, 7 May 2009

Slow Weblogic Response Part 3 - Tuning File Descriptors

This article is a follow-up to the Overall Tuning considerations discussed earlier.
A very important Operating System value to be tuned are the File Descriptors

File Descriptors and relation to Sockets

A File Descriptor (FD) is a handle created by a process when a file is opened. Each process can use a set limit of FDs and this is usually an OS level setting.
In the Solaris 8 version, the default is 1024. In later Solaris releases, the default is 65,536 but this needs to be set in the /etc/system as given below.
So, the default available for a process on an untuned OS is 1024.


# ulimit -a
time(seconds) unlimited
file(blocks) unlimited
data(kbytes) unlimited
stack(kbytes) 8192
coredump(blocks) unlimited
nofiles(descriptors) 2048
memory(kbytes) unlimited





In a JEE server, each incoming request uses a TCP socket and this socket consumes a file descriptor from the total available for the process.

As the number of requests coming into the server increase, you can face a situation where there are many sockets open and thus you run out of FDs
This could happen if you have a large number of clients (~1000 or more). This could also happen if you have HTTP connections with keep-alive turned off and so a lot of sockets are in TIME_WAIT.

If you have Stuck Threads, then those keep the FDs open and those wont be closed until the thread is released.

File Descriptors limit exceeded

A Weblogic server throws the below error when the FD limit has been exhausted.



BEA-000204 java.net.SocketException: Too many open files

OR

java.io.IOException: Too many open files
at java.lang.UNIXProcess.forkAndExec(Native Method)



When a Weblogic server starts up, there is an INFO message in the logs stating how many FDs have been allocated to the process.


<<WLS Kernel>> <> <BEA-000415> <System has file descriptor limits of - soft: 2,048, hard: 2,048>

<main> <<WLS Kernel>> <> <BEA-000416> <Using effective file descriptor limit of:

2,048 open sockets/files.>



To display a process' current file descriptor limit on Solaris, the command is:



/usr/proc/bin/pfiles <pid> grep rlimit

Example:

$/usr/proc/bin/pfiles 9052 grep rlimit

Current rlimit: 8192 file descriptors



You can check the actual number of FDs being used by a running server at any time using this command:




Note: This is not the max limit but the actual number used by the process at that point of time

ls /proc/<pid>/fd wc –l




If you monitor this on a regular basis, you can see how often you are nearing the max limit set, and whether the values need to be tuned to support the peak loads and peak traffic timings for your server.

As an example, we plotted FDs used every 5 minutes as below












Time

FD Used
11:00389
11:05429
11:10748
11:15488
11:20337
11:25595



Increasing File Descriptors

The Hard limit is the max value set on the OS.

The Soft limit shows the value set for a particular child process on the OS. This cannot be higher than the hard limit.
You can change the soft limit on-the-fly by using


ulimit -Sn 8192


This will only for that that telnet session and will not be a permanent change. Add this command to the user's .profile file to avoid repeating each time.

If hard limits need to be set, root user needs to update the /etc/system file and the machine to be rebooted. Even though the rlim_fd_max default on Solaris 9 is 65536, it must be in the /etc/system file

The values to be changed are

rlim_fd_max (default hard limit)
rlim_fd_cur (default soft limit)

On Linux:

To increase the hard limit it to (say) 65535, use the following command (as root):

echo "65535" > /proc/sys/fs/file-max

To make this value to survive a system reboot, add it to /etc/sysctl.conf and specify the maximum number of open files permitted:

fs.file-max = 65535


Any queries or clarifications, leave me a comment and I'll try to get back.

Wednesday, 6 May 2009

Slow Weblogic Response Part 2 - Overall Tuning Considerations




Part 1 of this article was related to using the JSP precompilation and tuning the recompilation settings provided in Weblogic.

Now, lets take a look at the other parameters that require tuning and setting correctly, in order for the Weblogic server to be generating acceptable performance of your site.

Usually the problem statement is similar to this:

1. The site regularly stops responding and all available execute threads are consumed. All future requests fail to be handled and a server restart is required.
2. The page response times of the entire site are too high and need to be brought down to a more useable level.

Note: An additional post has been published which provides a skeleton Action Plan for analyzing the entire slow site/high CPU issue including managing stakeholder expectations and appropriate reporting.

Operating System Review
A review of the Operating System configuration needs to look at
a) The number of file descriptors available and whether that matches the value recommended for Weblogic
b) Various TCP settings (also called NDD parameters) which will affect how long it takes to recycle a closed or dropped connection.
2 top settings are:
• File Descriptor limit: increase to 8192 if not 65536. A detailed follow-up on File Descriptors is published here.
• tcp_time_wait_interval: change to 60000 [The default in Solaris 8 is 4 minutes used to keep a socket open in TIME_WAIT state, even after the response is provided to the client, set this down to 1 minute. The default in Solaris 9 is 1 minute]
Check the Oracle site for the latest recommended values

Database Usage and JDBC Drivers
a) If you get Out Of Memory errors occurring in JDBC calls, it is recommended that the JDBC driver be upgraded to the latest version.

b) Prepared Statement caching is a feature that allows prepared statements to be held in a cache on the database so they do not have to be re-parsed for each call. This functionality needs to be enabled per Connection Pool and can have a significant impact on the performance of the pools. But this needs to be validated with a focussed round of Performance testing.

It should be noted that for every Prepared Statement that is held in cache, a cursor is held open on the database for each connection in the pool. So if a cache size of 10 is used on the abcPool, and the pool has a size of 50 then 500 open cursors will be required. Repeatable load tests will highlight any gains achieved by enabling this caching.

Review JDBC Pool Sizes
Review connection pool versus the number of Execute threads. Usually keep Pool size close to Execute thread size. Note: This applies to versions earlier than Weblogic 9. See detailed explanation below.

If the JDBC pool size is quite less compared to the Thread size, there is the potential to negatively impact performance quite dramatically, since threads have to wait for connections to be returned to the pool.
Your most frequently used pool should have their minimum (initial) and maximum sizes increased to the number of Execute threads plus one. This will mean there is an available connection for every thread.
One comment on pool sizing it is beneficial where ever possible to have the initial and max connections set to the same size for a JDBCPool as this avoids expanding/shrinking work that can be costly, for both the establishment of new connections while expanding the pool and housekeeping work for the pool.

However it is also recommended to monitor the JDBC pools during peak hours and see how many connections are being used at maximum. If you are not hitting the MaxCapacity, it is useful to reduce the MaxCapacity to avoid unnecessary open cursors on the database.

Note: As of Weblogic 9 and higher, Execute Queues are now replaced by Work Managers. Work Managers can be used for JDBC pools by defining the max-threads-constraint to define how many threads to allocate for a particular Datasource.
It is possible to run Weblogic 9 and 10 with the Execute Queues as available earlier. This is not recommended since Work Managers are self-tuning and more advanced than Execute Threads.

WebLogic Server, Version 8.1, implemented Execute Queues to handle thread management in which you created thread-pools to determine how workload was handled. WebLogic Server still
provides Execute Queues for backward compatibility, primarily to facilitate application
migration. However, when developing new applications, you should use Work Managers to perform thread management more efficiently.
You can enable Execute Queues in the following ways:
􀁺 Using the command line option
-Dweblogic.Use81StyleExecuteQueues=true
􀁺 Setting the Use81StyleExecuteQueues property via the Kernel MBean in config.xml.
Enabling Execute Queues disables all Work Manager configuration and thread self tuning.
Execute Queues behave exactly as they did in WebLogic Server 8.1.


Database Persistent JMS Queues

Verify whether the database architecture is such that persistent JMS queues use the same database instance as a message store as your Weblogic portal uses for data.
As the volumes on these queues increase this could significantly degrade the performance of the portal by competing for valuable CPU cycles on the database server.

1. Move the message store for persistent queues to a separate database instance from that used by most of the JDBC pools belonging to the Weblogic server. This will prevent increases in message volumes from adversely affecting the performance of the database, which would also slow the portal applications down and vice-versa.

2. Implement paging with a file-store. This allows the amount of memory consumed by JMS queues to be restricted by paging message contents to disk and only holding headers in memory. Note that this does not provide failover protection in the way persistence does and performs better with a paging file-store than a paging JDBC store.

3. It is recommended that a review is also undertaken to determine exactly which queues are persisted and whether they truly need to be. The performance gains from switching to non-persisted queues are substantial, and guaranteed delivery is not always required.

Review Number of Execute Threads
A common mistake made by Support teams when seeing Stuck threads is to increase the number of execute threads in a single ‘default’ queue. At one time, I have worked in a project which ran the Weblogic server with 95 threads.

This figure is very high and results in a large amount of context-switching as load increases, which consumes valuable CPU cycles. Because threads consume memory, you can degrade performance by increasing the value of the Thread Count attribute unnecessarily.

Taking a Thread Dump when the server is not responding will show what the threads are doing, and help identify whether there is an application coding issue or deadlock occuring. Use Samurai to analyze these as earlier posted
It is recommended that regular monitoring of the number of idle threads and the length of queued requests for each execute queue is set up via MBeans. This allows the Support teams to plot a graph of utilization and validation of any changed values.
Note: As of Weblogic 9 and higher, Execute Queues are now replaced by Work Managers. Another good link is here

Use Dedicated Execute Thread Queue for Intensive applications

As the number of threads is small, and if a particular application is seen to utilize a majority of the execute, the following 2 approaches are suggested to resolve the issue:
1. Review the design of the offending application to determine whether it really needs so many threads.
2. Move the offending application to a dedicated execute queue, with enough threads allocated to this queue. This will prevent it from starving the main server of threads and allow the ‘default’ queue to remain with a lower number of Execute threads. This split of Execute Queue can be done at servlet or webapp level. Mail me if you need an example, we've done both successfully in WL 8.1 and 9.

Note: However, as of Weblogic 9 and higher, Execute Queues are now replaced by Work Managers. You can use a Work Manager to dedicate resources at Application, Web App, EJB level.


Review Java VM Settings
Tuning the JVM settings for the Total Heap, and Young/Old Generations is essential to regulate the frequency of Garbage Collection on the servers. The basic primer is on the Sun website, and a follow up of actual values and learnings is published here. The most essential ones are Xms, Xmx for the total Heap and NewSize, NewRatio for the Young Generation. Also set PermSize and MaxPermSize appropriately to avoid consuming high memory

Other Areas

1. To speed up server start times, do not delete the .wlnotdelete directories at startup - Unless you are deploying changed application jars and code.
Be aware you might occasionally see a problem shutting down the server which goes into an UNKNOWN state due to too many old temp files and wl_internal files.
You will get the dreaded error below which can only be resolved by killing the process and clearing out all temp files, .lck files etc within the domain. The files are under DOMAIN_HOME/servers//



weblogic.management.NoAccessRuntimeException: Access not allowed for subject: principals=[weblogic, Deployers], on ResourceType: ServerLifeCycleRuntime Action: execute, Target: shutdown
at weblogic.rjvm.ResponseImpl.unmarshalReturn(ResponseImpl.java:195)
at weblogic.rmi.internal.BasicRemoteRef.invoke(BasicRemoteRef.java:224)



2. Avoid the URLEncoder.encode method call as much as possible. This calls is not optimal in most JDKs < 1.5 and is often found as memory and CPU hotspot issue.

3. Check the network connection between WebLogic and the database. If Thread dumps show that threads are often in a suspended state (waiting for so long that they were suspended) while doing a socket read from the database.
The DBA wouldn't see this as a long-running SQL statement. This needs to be checked out at the network level.

4. Switch off all DEBUG options on Production on app server as well as web server and web server plugins.

5. Ensure log files are rotated so that they can be backed up and moved off the main log directory. Define a rotation policy based on file size or fixed time (like 24 hours)
However also note that: On certain platforms, if some application is tailing
the log at the time of rotation, the rotation fails. Stop the application tailing and reopen the tail after the rotation is complete.

6. Do not use "Emulate Two-Phase Commit for non-XA Driver" for DataSources.
It is not a good idea to use emulated XA. It can result in loss of data integrity and can cause heuristic exceptions. This option is only meant for use with databases for which there is no XA driver so that the datasources for these pools can still participate in XA transactions.
If an XA driver is available (and there is for Oracle), it should be used. If this option is selected because of problems with Oracle's Thin XA driver, try the newest version, or pick a different XA driver.

7. The <save-sessions-enabled> element in web.xml controls whether session data is cleaned up during redeploy or undeploy.
It affects memory and replicated sessions. The default is false. Setting the value to true means session data is saved and this is an overhead.

8. If firewalls are present between Weblogic server and the database or an external system connecting via JMS, this can cause transactional and session timeout issues. The session timeout on the firewall shoudl be configured to allow for normal transaction times.
In the case of JMS, transactional interoperation between the two servers can be compromised and hence it is beneficial to open the firewall between the two servers so that RMI/T3 connections can be made freely.


Any queries or clarifications, leave me a comment and I'll try to get back.

Slow Weblogic response - JSP and Servlet Reload

The top Weblogic tuning tip I've used over the last few years is the one below. This article deals with Weblogic 8 and 9.

You know the symptoms:

JEE Application works okay on Unit Integration and Test servers.
But once you're into Performance and Stress Testing - it's totally choked up - pages are returned so slowly - Project Manager is asking for a code review to find the blockers - etc.


The first thing to do on a slow JEE application is to take a thread dump, see more on that here

Now, the thing to look for in the Thread Dump, is multiple threads doing this:


weblogic.servlet.jsp.JspStub.checkForReload(JspStub.java:144)


or this:


waiting for monitor entry [c4f7f000..c4f7fc28]
at weblogic.servlet.internal.ServletStubImpl.checkForReload(ServletStubImpl.java:771)




This is not a stuck thread within your code – but this is a weblogic.xml setting for checking each time if your servlet class or JSP has been changed.

As documented here:

http://e-docs.bea.com/wls/docs92/webapp/weblogic_xml.html#wp1038491

Sets the interval, in seconds, at which WebLogic Server checks to see if JSP files have changed and need recompiling. Dependencies are also checked and recursively reloaded if changed.

If set to 0, pages are checked on every request. If set to -1, page checking and recompiling is disabled.

Most users set this to -1 to disable in Production unless they're altering jsps on the fly (which is not normal practice on a production system).


The correct syntax for this is:

<weblogic-web-app>
<jsp-descriptor>
<jsp-param>
<param-name>pageCheckSeconds</param-name>
<param-value>-1</param-value>

</jsp-param>
</jsp-descriptor>

The similar value for servlets is set using the servlet-reload-check-secs within the tags below.

<container-descriptor>
<servlet-reload-check-secs>-1</servlet-reload-check-secs>
</container-descriptor>
</weblogic-web-app>


On non-production environments, you can set this to a reasonable value such as 600 (in seconds, which is 10 minutes) to allow for changed JSPs you drop in/FTP to the deployed environment, and want those to reflect sooner.

The other thing we must do on a production system is to precompile the JSPs as part of the build, and before deploying to Live.

Else, even the first time JSP compilation is quite slow and this must be avoided on the Production system.


For the same solution on Weblogic 10, look at an updated article.