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11. HTTP and TCP/IP Configuration Tips: Information to assist with the configuration for TCP/IP
and HTTP can be viewed at
http://www.ibm.com/servers/eserver/iseries/software/http/
a. The number of HTTP server threads: The reason for having multiple server threads is that
when one server is waiting for a disk or communications I/O to complete, a different server job
can process another user's request. Also, if persistent requests are being used and AsyncIO is Off,
a server thread is allocated to that user for the entire length of the connection. For N-way
systems, each CPU may simultaneously process server jobs. The system will adjust the number of
servers that are needed automatically (within the bounds of the minimum and maximum
parameters). The values specified are for the number of "worker" threads. Typically, the default
values will provide the best performance for most systems. For larger systems, the maximum
number of server threads may have to be increased. A starting point for the maximum number of
threads can be the CPW value (the portion that is being used for Web server activity) divided by
20. Try not to have excessively more than what is needed as this may cause unnecessary system
activity.
b. The maximum frame size parameter (MAXFRAME on LIND) is generally satisfactory for
Ethernet because the default value is equal to the maximum value (1.5K). For Token-Ring, it can
be increased from 1994 bytes to its maximum of 16393 to allow for larger transmissions.
c. The maximum transmission unit (MTU) size parameter (CFGTCP command) for both the route
and interface affect the actual size of the line flows. Optimizing the MTU value will most likely
reduce the overall number of transmissions, and therefore, increase the potential capacity of the
CPU and the IOP. The MTU on the interface should be set to the frame size (*LIND). The MTU
on the route should be set to the interface (*IFC). Similar parameters also exist on the Web
browsers. The negotiated value will be the minimum of the server and browser (and perhaps any
bridges/routers), so increase them all.
d. Increasing the TCP/IP buffer size (TCPRCVBUF and TCPSNDBUF on the CHGTCPA or
CFGTCP command) from 8K bytes to 64K bytes (or as high as 8MB) may increase the
performance when sending larger amounts of data. If most of the files being served are 10K
bytes or less, it is recommended that the buffer size is not increased to the max of 8MB because it
may cause a negative effect on throughput.
e. Error and Access Logging: Having logging turned on causes a small amount of system overhead
(CPU time, extra I/O). Typically, it may increase the CPU load by 5-10%. Turn logging off for
best capacity. Use the Administration GUI to make changes to the type and amount of logging
needed.
f. Name Server Accesses: For each Internet transaction, the server accesses the name server for
information (IP address and name translations). These accesses cause significant overhead (CPU
time, comm I/O) and greatly reduce system capacity. These accesses can be eliminated by editing
the server's config file and adding the line: "HostNameLookups Off".
12. HTTP Server Memory Requirements: Follow the faulting threshold guidelines suggested in the
work management guide by observing/adjusting the memory in both the machine pool and the pool
that the HTTP servers run in (WRKSYSSTS). Factors that may significantly affect the memory
requirements include using larger document sizes and using CGI programs.
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
©
Copyright IBM Corp. 2008
http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp
Chapter 6 - Web Server and WebSphere
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