Sun Microsystems Sun Java System Web Server 7.0, Manual

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Low-Memory Situations
If Web Server must run in low-memory situations, reduce the thread limit to a bare minimum
by lowering the value of the Maximum Threads setting on the configuration's Performance Tab
⇒
HTTP sub tab. You can also set it with
wadm set-thread-pool-prop
command's
max-threads
property.
Your web applications running under stress might sometimes result in the server running out
of Java VM runtime heap space, as can be seen by
java.lang.OutOfMemoryError
messages in
the server log file. There could be several reasons for this (such as excessive allocation of
objects), but such behavior could affect performance. To address this problem, profile the
application. Refer to the following HotSpot VM performance FAQ for tips on profiling
allocations (objects and their sizes) of your application:
http://java.sun.com/docs/hotspot/index.html
At times your application could be running out of maximum sessions (as evidenced by a “too
many active sessions” message in the server log file), which would result in the container
throwing exceptions, which in turn impacts application performance. Consideration of session
manager properties, session creation activity (note that JSPs have sessions enabled by default),
and session idle time is needed to address this situation.
Too Few Threads
The server does not allow the number of active threads to exceed the thread limit value. If the
number of simultaneous requests reaches that limit, the server stops servicing new connections
until the old connections are freed up. This can lead to increased response time.
In Web Server, the server’s default maximum threads setting is 128. If you want your server to
process more requests concurrently, you need to increase the maximum number of threads.
The symptom of a server with too few threads is a long response time. Making a request from a
browser establishes a connection fairly quickly to the server, but if there are too few threads on
the server it might take a long time before the response comes back to the client.
The best way to tell if your server is being throttled by too few threads is to see if the number of
active sessions is close to, or equal to, the maximum number of threads. To do this, see
“Session
Creation (Thread) Information” on page 57 .
Low-Memory Situations
Sun Java System Web Server 7.0 Update 1 Performance Tuning, Sizing, and Scaling Guide • 86