We are expanding the service to meet this growth in demand. We are also undedrtaking some service enhancements to improve performance. The current service is provided by over 30 Intel-based machines running the Linux and FreeBSD operating systems and Squid caching software. Each node comprises several machines which cooperate with each other using the Cache Digest mechanism. Institutions are allocated machines at two of these nodes and thereby access to the aggregate filestore at each node comprising hundreds of GBytes of cached information.
Many factors influence the effectiveness of the caching service.
The former results in users observing unacceptably high Web object retrieval response times whilst the latter imposes unecessary processing load on the caches, also resulting in increased response times. One way of reducing response times in general and during periods of peak demand in particular, is to balance the load being processed by a cluster of caches. Tests with several volunteer sites have indicated that this mechanism is very effective in reducing object retrieval times during periods of peak demand. Accordingly during the next few months we will transition the national caching service to an LVS based system, details of which are available at our web site at the URL listed below. Also in the coming months we plan to improve response times further still by addressing the problem of caches handling requests for non-cacheable objects.