Dynamic caching

In general, caching improves response time and reduces system load. Caching techniques have long been used to improve the performance of World Wide Web Internet applications. Most techniques cache static content (content that rarely changes) such as graphic and text files. However, many Web sites serve dynamic content, containing personalized information or data that changes more frequently. Caching dynamic content requires more sophisticated caching techniques, such as those provided by the WAS 6.0 dynamic cache, a built-in service for caching and serving dynamic content.

The dynamic cache service includes :

• Servlet and/or JSP result cache, to cache whole pages or fragments generated by a Servlet or a JSP page.

• Command cache, to cache command objects.

• Edge Side Include (ESI) caching, to cache, assemble and deliver dynamic web pages at the edge of an enterprise network.

• Invalidation Support, to ensure the content of the cache is correct. Invalidation can be rule-based, time-based, group-based, and programmatic.

• Replication support, to enable cache sharing and replication among multiple servers.

• Disk offload capability, to enable caching large amounts of data, and to preserve cache content while the application server is stopped and restarted.
  

  After the application server is restarted and the database restored, IBM recommends that you clear the disk cache using the cache monitor. This will ensure that information that has become invalid for the new database is removed. Use the cache monitor to clear the cache or, alternatively, use the following URL: http:// host_name/path/DynaCacheInvalidation?clear=true. For more information, see DynaCacheInvalidation URL.

The caching behavior of the WAS dynamic cache service is specified by cache policies defined by <cache-entry> elements in cache specification configuration XML (cachespec.xml) files.

As the dynamic cache service places objects in the cache, it labels them with unique identifying strings (cache IDs) constructed according to <cache-id> rules specified in the <cache-entry> elements. Once an object with a particular cache-id is in the cache, a subsequent request for an object with the same cache-id is served from the cache (a cache "hit"). The <cache-id> rules define how to construct cache-ids from information associated with an application server request (to execute a Servlet, JSP, or command), including how information may be obtained programmatically from CacheableCommand objects.

Cached objects are removed from the cache according to information provided in their <cache-entry> elements, such as the <timeout>, <priority> and <invalidation> elements.

The <timeout> and <priority> elements configure expiry and eviction policies. When the available cache memory is full, a least recently used (LRU) caching algorithm removes cached objects with lower priority, or offloads them to disk if the disk offload capability is enabled, before those with higher priority.

The <dependency-id> and <invalidation> elements define rules that generate dependency IDs and invalidation IDs, which together specify that certain objects should be removed from the cache when certain requests (such as those that update cached information) are processed. When an object is cached, its generated dependency IDs are associated with it in the cache. When a request causes invalidation IDs to be generated, all objects associated with those invalidation IDs are removed from the cache.

The <inactivity> element is used to specify a time-to-live (TTL) value for the cache entry based on the last time that the cache entry was accessed. The value is the amount of time, in seconds, to keep the cache entry in the cache after the last cache hit.

The dynamic cache service responds to changes in the cachespec.xml file. When the file is updated, the old policies are replaced. Objects cached through the old policy file are not automatically invalidated from the cache; they are either reused with the new policy or eliminated from the cache through its replacement algorithm.

WebSphere Commerce uses WebSphere Command Caching internally such as with MemberGroupsCacheCmdImpl in the preceding cache filter; however, WebSphere Commerce does not support caching of commands that contain non-serializable objects.

 

WAS dynamic cache

WebSphere Commerce uses the WAS dynamic cache service for caching servlets or JSP files and commands that extend from the WebSphere Application Server CacheableCommand interface. The dynamic cache service, servlet caching and disk offload are enabled by default, during the creation of a WebSphere Commerce instance.

 

Related Concepts

Cache invalidation

 

Related tasks

Configure cacheable objects
Create store pages that can be cached using cachespec.xml

 

Related Reference

Caching defaults
DynaCacheInvalidation URL
WebSphere Commerce store pages properties