Recommended Configurations

  Combining the above results, we recommend the following configuration for the summary cache approach. The update threshold should be between 1% and 10% to avoid significant reduction of total cache hit ratio. If a time-based update approach is chosen, the time interval should be chosen such that the percentage of new documents is between 1% and 10%. The proxy can either broadcast the changes (or the entire bit array if it is smaller), or let other proxies fetch the updates from it. The summary should be in the form of a Bloom filter. A load factor between 8 and 16 works well, though proxies can lower or raise it depending on their memory and network traffic concerns. Based on the load factor, four or more hash functions should be used. The data provided here and in [16] can be used as references in making the decisions. For hash functions, we recommend taking disjoint groups of bits from the 128-bit MD5 signature of the URL. If more bits are needed, one can calculate the MD5 signature of the URL concatenated with itself. In practice, the computational overhead of MD5 is negligible compared with the user and system CPU overhead incurred by caching documents (see Section 7).