What are False Hits and how should they be handled?
A False Hit occurs when a cache believes a peer has an object and asks the peer for it but the peer is not able to satisfy the request. Expiring or stale objects on the peer are frequent causes of False Hits. At the time of the query actual refresh patterns are used on the peer and stale entries are marked for revalidation. However, revalidation is prohibited unless the peer is behaving as a parent, or miss_access is enabled. Thus, clients can receive error messages instead of revalidated objects! The frequency of False Hits can be reduced but never eliminated completely, therefore there must be a robust way of handling them when they occur. The philosophy behind the design of Squid is to use lightweight techniques and optimise for the common case and robustly handle the unusual case (False Hits). Squid will soon support the HTTP only-if-cached header. Requests for objects made to a peer will use this header and if the objects are not available, the peer can reply appropriately allowin
