Real time issues on WAS

1.Issue:

Hang/slowness in IBM WebSphere Application Server Administrative console to check the status of application servers or application

Cause :

When the server status page is accessed, deployment manager will communicate with all node agents to get the server status. This could take long time. The status of the servers are not cached. So, if there are lot of servers, you will notice significant amount of delay in loading status of all servers.

Go to was console -expand system administration -JVM Settings > System Property > New

1. Add a new Custom Property for JVM to cache the local host information:
   System Property Name: com.ibm.cacheLocalHost
   System Property Value: true
2. save changes and restart the dmgr

2.There is slow performance or a hang during HostName lookup

Symptom

Thread dumps or javacores taken during the time of the slow response, or "hang threads" will show threads with the following lines at the top of the stack:

at java.net.Inet6AddressImpl.getLocalHostName(Native Method)
at java.net.InetAddress.getLocalHost(InetAddress.java:123)

Cause

The problem could be lookup issues between IPv6 versus IPv4. If the Domain Name System (DNS) server is not configured to handle IPv6 queries, the application may have to wait for the IPv6 query to time out for IPv6 queries.

These threads are waiting for a response for an IPv6 query. It is likely the the DNS server is not responding to the IPv6 query.

Resolving the problem

If your environment only uses IPv4, set the following argument for each process:

-Djava.net.preferIPv4Stack=true 

This will disable IPv6 lookup requests and only use IPv4. To set this in the WebSphere Application Server, do the following:

• 1. Open the administrative console and navigate to:
     
     Servers > Application Servers > server_name > Process Definition > Java Virtual Machine > Custom Properties(/Environment Entries)
  2. Add the following name and value pair:
     
     Name: java.net.preferIPv4Stack
     Value: true
  3. Click Apply, then save all changes.
  4. Restart the application server.
• If your environment uses IPv6, please have your network administrator check the DNS set up to ensure that it can respond properly to IPv6 queries.

3.Tuning IBM HTTP Server to maximize the number of client connections to WebSphere Application Server

Problem(Abstract)

Out of the box, IBM HTTP Server supports a maximum of 600 concurrent connections. Performance will suffer if load dictates more concurrent connections, as incoming requests will be queued up by the host operating system.

You can increase the number of maximum connections allowed by IBM HTTP Server by editing the httpd.conf file.

Resolving the problem

First and foremost, you must determine the maximum number of simultaneous connections required for this Web server. Using mod_status ormod_mpmstats (available with ihsdiag) to display the active number of threads throughout the day will provide some starting data.

There are 3 critical aspects to MPM (Multi-processing Module) tuning in IBM HTTP Server.

1. Configuring the maximum number of simultaneous connections (MaxClients directive)
2. Configuring the maximum number of IBM HTTP Server child processes (ThreadsPerChild directive)
3. Less importantly, configuring the ramp-up and ramp-down of IBM HTTP Server child processes (MinSpareThreads, MaxSpareThreads, StartServers)

The first setting (MaxClients) has the largest immediate impact, but the latter 2 settings help tune IBM HTTP Server to accommodate per-process features in Apache modules, such as the WebSphere Application Server Web server plug-in.