Understanding cache hierarchies
Cache hierarchies consist of levels of caches that communicate with each other. Hierarchical caching can give you information about the local access requirements of your users; this information might not appear in a large central cache. The Intel NetStructure Cache Appliance supports several types of cache hierarchies, but all cache hierarchies recognize the concepts of parent and child caches.
In a cache hierarchy a parent cache is a cache higher up, to which the appliance can forward requests. A child cache is a cache lower down for which the appliance is a parent.
In the event of a cache miss, instead of forwarding the request to a distant origin server, it might be faster to try another nearby cache in the hierarchy. If a forwarded request is a miss on the parent cache, the parent cache forwards the request to the origin server. See Figure 7‚ on page 136 for an illustration. The appliance supports multiple parent caches; if a request misses on all parents, the appliance chooses a specific parent to forward the request to the origin server.
The Intel NetStructure Cache Appliance can function as a member of the following cache hierarchies:
✔HTTP cache hierarchy
✔ICP (Internet Cache Protocol) hierarchy
✔NNTP hierarchy
The following sections describe these cache hierarchies.
HTTP cache hierarchies
The Intel NetStructure Cache Appliance supports HTTP cache hierarchies, using other Intel NetStructure Cache Appliances or even other caching products as parents or children in a chain of interdependent caches.You can create small, regional caches (for an organizational department or for users in a defined geographic area), and link them to larger parent caches, defining larger areas.
If a regional cache does not have a requested document (a cache miss) and HTTP parent caching is enabled, the appliance forwards the HTTP request to a parent cache in the hierarchy rather than contacting the origin server. If the parent cache (or caches) cannot serve the object they can forward the request to other caches further up in the hierarchy.
The appliance supports multiple HTTP parent caches and parent failover. This feature gives the appliance a sequence of parent caches to query if the first parent cache misses.
Appendix A Caching Solutions and Performance | 135 |
