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Content-Layer Overhead

We measured an overhead of 0.5 milliseconds (total for both request and response) for going through a single hop of the content routing layer, on a name routing table of 5 million entries stored entirely in memory. The 5 million names were randomly generated second-level domain names, with 80% in .com and 10% in each of .org and .net; a uniform distribution of name lengths between 3 and 17 was used. These names were divided into aggregates of 15,000.

Measurements done on the 1.7 million-name database from our aggregation experiment show no significant difference in overhead. Profiling information shows that most of this time is spent doing packet processing; measurements on the actual routing table show that route lookup takes as little as 6 microseconds. Our implementation can easily sustain a throughput of 650 requests/second without any degradation of response time, and peak throughput of 1600 requests/second.

The total amount of memory used by the content router for a 5 million entry table was 344MB, while that on a similarly generated 100,000 entry (but unaggregated) table was 20MB. This leads to an estimate of 69 bytes per routing table entry. We can extrapolate that a 30-million entry database would require nearly 2GB of memory; while large, this is not an infeasible amount of DRAM, costing only about $4000. (It is worth noting that name lookups which must go to the DNS root already encounter a database lookup of approximately this size.)

Mark Geoffrey Gritter
Fri Jan 19 09:19:43 PST 2001