Tomcat Manager is a Webapp included in all standard distributions of Apache Tomcat that allows a new web application to be deployed or an existing web application to be undeployed without having to shut down and restart the entire container.
With regards to using the Tomcat Manager to monitor a PASOE instance from the Front End point of view, the Server Status option is the one focused on this article.
In order to access the Tomcat Manager Server Status option (provided that the Tomcat Manager Webapp has been deployed to the PASOE instance):
1) Start a web browser
2) Connect to the PASOE Instance by putting its URL in the web browser like in <PASOE_Instance_IP>:<Port>/manager
3) Tomcat Manager will request a user and password to check permissions
4) Tomcat Web Application Manager will be presented. Click on the Server Status option presented on the right side of this page
The Server Status page presents a plethora of useful information, but it will be focused on the following ones for the moment:
Java Heap Memory Utilization
Below the JVM Section there will be the following information regarding the Java Heap Memory configured and utilized:
Free memory: <value> MB
Total memory: <value> MB
Max memory: <value> MB
This information is relevant because if Free memory gets too low and remains low for a considerable period of time affecting PASOE instance performance, it may indicate that more Java Heap Memory is needed.
In this case, -Xms and -Xmx properties in the <CATALINE_BASE>\conf\jvm.properties file may be increased to provide more Java Heap memory for a given PASOE instance.
Thread Information:
Other relevant information presented by the Server Status page are:
Max threads: <value>
Current thread count: <value>
Current thread busy: <value>
Keep alive sockets count: <value>
In this case, if the Current thread busy gets closer to the Current Max Threads and remains in this condition for a considerable period of time, then the performance of a given PASOE instance may be affected as more incoming requests are getting to the PASOE instance but the instance itself is already busy handling other previous requests. This may be an indication that the number of threads currently set up is not enough to handle the load. If that is the case, psc.as.executor.maxthreads may be increased to make more room for this load in terms of maximum number of OS process threads this server will use. Use <CATALINA_BASE>/bin/tcman.sh config psc.as.executor.maxthreads=<new_number_of_threads> to increase the number of max threads.
Processing Times
Other very useful information presented by the Server Status page is the processing times information, request count information and error count:
Max processing time: <value> ms
Processing time: <value> s
Request count: <value>
Error count: <value>
Bytes received: <value> MB
Bytes sent: <value> MB
The values above present information about how long a request took to complete, how many requests the PASOE instance has gotten so far, the number of errors occurred. Very useful information that allows comparison with previous baselines to check and confirm problems like if a performance problem has taken place or not, if a given day, the number of requests is too high or too low, etc.
The purpose of this article is to introduce the ability the Tomcat Manager Webapp provides to help monitor a PASOE instance/application. For more in-depth information on how to tune a PASOE instance refer to the article in the notes section below. For more in-depth information on the Tomcat Manager, refer to the Apache Tomcat product documentation.
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