About LSAM Request Routing

Multi-path Request Forwarding (aka Cut-Through)

Given a cache hierarchy with multiple levels, there is a possibility that a series of cache misses will add an undesirable amount of delay in responding to a client request. The cost of this delay must be weighed against the benefits of getting the requested file from a cache.

Our approach is based on the ability to make background, as well as foreground, cache requests. LSAM is developing differentiated service mechanisms that will allow high and low priority requests to be made and serviced. This will allow LSAM Request Forwarding to, for example, make a normal priority request within the cache hierarchy, and a simultaneous lower-priority request to the origin server. Ideally, the low-priority request will be dropped if the origin server is overloaded, but will generate a lower-delay response if the request misses in several levels of cache.

Based on the differentiated services provided as another component of the LSAM proxy, Request Routing must address issues such as (a) when should requests be forwarded to multiple servers, and (b) how do we avoid a request from generating multiple queries directly to the origin server.

These mechanisms are under development.

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