Intel 7xx Servers Cache Size Effect, Definitions would be retained in the cache with few cache

When set to an appropriate level for the Webfaced application, the Record Definition Cache can provide a decrease in memory usage, and slightly decreased processor usage. The number of record definitions that the cache will retain is set by an initialization parameter in the Webfaced application’s deployment descriptor (web.xml). By changing the cache size, the Webfaced application can be tuned for best performance and minimum memory requirements. The cache size determines the number of record data definitions that will be retained in the cache. There is one record data definition for each record format.

Cache Size	Effect
too small	When the cache size is set too small for the Webfaced
	application it will adversely affect the performance. In this
	case, the definitions would be cached then discarded before
	being re-used. There is significant overhead to create the
	record definitions.
correct	With the cache set correctly, 90% of all accessed record data
	definitions would be retained in the cache with few cache
	misses for not commonly used records.
too large	If the cache is set too large then all record data definitions
	for the Webfaced application would be cached, likely
	consuming memory for seldom used definitions.

In order to determine what is the correct size for a given Webfaced application, the number of commonly used record formats needs to estimated. This can be used as a starting point for setting the cache size. The default size, if no size is specified, would be 600 record data definitions. To set the cache size to something other than the default size, you need to add a session context parameter in the Webfaced application’s web.xml file. In the following example the cache size is set to 200 elements, which may be appropriate for a very small application, like the Order Entry example program.

<context-param> <param-name>WFBeanCacheSize</param-name> <param-value>200</param-value>

<description>WebFacing Record Definition Bean Cache Size</description> </context-param>

NOTE: For information on defining a session context parameter in the web.xml file, refer to the WebSphere Application Server Info Center. You can also edit the web.xml file of a deployed application. Typically this file will be located in the following directory for WebSphere V5.0 applications:

/QIBM/UserData/WebAS5/Base/<application-server>/config/cells/..../WEB_INF

And the following directory for WebSphere Express V5.0 applications:

/QIBM/UserData/WebASE/ASE5/<application-server>/config/cells/..../WEB_INF

Cache Management - Definition Cache Content Viewer

To assist with managing the Record Definition Cache, two servlets can be enabled. One is used to display the elements currently in the cache and the other can be used to load the cache. Both of these servlets are not normally enabled in a WebFacing application in order to prevent mis-use or exposure of data.

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 6 - Web Server and WebSphere	110