Apple WebObjects 3.5 - Manual (Page 136)

Chapter 7 Managing State
136
Adjusting the Page Cache Size
As noted in “WebObjects Viewed Through Its Classes” (page 63), except for the
first request, a request to a WebObjects application contains a session ID, page
name, and context ID. The application uses this information to ask the
appropriate session object for the page identified by the name and context ID.
As long as the page is still in the cache, it can be retrieved and enlisted in
handling the request.
By default, a WebObjects application caches the last 30 pages that a user has
visited within a session. You can change the size of the cache using the
application object’s
setPageCacheSize: method and retrieve the cache size with the
pageCacheSize method. Within each session, new pages are added to the cache until
the cache size limit is reached. Thereafter, for each new page added to the
cache, the cached page object representing the least recently visited page is
released.
To reduce the resource requirements for an application, you could set the page
cache to a smaller number. However, doing so increases the possibility that a
request could address a page that is no longer in the cache. For example, if you
set the page cache size to four, a user could backtrack five pages to an order form,
make some changes, and resubmit the form. The result would be an error page
like this:
Figure 36. Backtracking Error Message
To keep users from encountering this error, your application should maintain a
moderate sized cache of pages. (Another strategy is to limit the number of
identical page instances that your application creates; see “pageWithName: and
Page Caching” (page 138) for one way to do this.) The default cache size of 30
pages is a reasonable value that protects users from reaching the backtracking
limit under normal conditions; however, you can adjust the limit to any positive
value you like or even zero.
Setting the page cache size to 0 has two effects. As expected, it disables page
caching. Furthermore, it signals to WebObjects that you intend to provide for
component state persistence rather than rely on WebObjects’ inherent support.
Thus, if you set the cache size to 0, no error page is generated if a request
addresses a page that can’t be found in the cache. Instead, WebObjects creates
a new page by sending the application object a
pageWithName: message. Since with
this model pages do not persist from one request to the next, you assume