WebSphere external caching scenarios
The objectives of our external caching scenarios are:
| Describe the external caching options |
| Configure and test external caching options |
| Explore cache invalidation |
We use the following external caches, which can be controlled by the WebSphere dynamic cache service:
In addition to the well known Web server plug-in functionalities (such as failover and load balancing), the Web server plug-in is integrated with the WebSphere Dynamic Cache to provide in-memory caching of servlets and JSP pages. It uses the ESI fragment assembly, which further enhances this caching ability with on-the-fly reassembly of JSP pages.
This cache is referred to as the Fast Response Cache Accelerator (FRCA) to cache whole pages and fragments.
The Edge Components can also be configured as WAS's external cache for whole page caching. In this case, the dynamic cache service can be enabled to match pages with their universal resource identifiers (URIs) and export matching pages to the external cache (Figure 14-28). The contents can then be served from the external cache instead of the appserver to significantly save resources and improve performance.
Figure 14-28 and Figure 14-29 show two examples of exporting a dynamic cache page from the WAS to the external cache.
The first example (Figure 14-28) shows caching of whole pages, where page A.jsp consists of three fragments. These three JSPs are included at compilation time. The event-driven invalidation causes the invalidation of A.jsp from the external cache as a result of any update to B.jsp, C.jsp, or D.jsp.
Figure 14-28 Whole page external caching
The second example (Figure 14-29) shows caching of a whole page and its' fragments using Edge Side Include (ESI). In this case, if a fragment (for example B.jsp) is invalidated by event-driven or time-driven invalidation, then the page A.jsp is not invalidated and ESI will tell the cache server to fetch only the invalidated fragment (B.jsp) from the appserver. Then, the external cache using the ESI processor assembles a new page A.jsp which consists of the old fragments C.jsp and D.jsp and the new fragment B.jsp.
Figure 14-29 Fragment external caching
For example, the Trade3 home servlet contains fragment marketSummary.jsp. If we invalidate marketSummary.jsp, only this JSP will be regenerated upon the next request for the home servlet.
Any servlet and JSP file content that is private, requires authentication, or uses SSL should not be cached externally. The authentication required for those servlet or JSP file fragments cannot be performed on the external cache. A suitable timeout value should be specified if the content is likely to become stale.
WebSphere is a trademark of the IBM Corporation in the United States, other countries, or both.
IBM is a trademark of the IBM Corporation in the United States, other countries, or both.