NSDI '05 Abstract
Bandwidth-efficient Management of DHT Routing Tables
Jinyang Li, Jeremy Stribling, Robert Morris, and M. Frans Kaashoek,
MIT Computer Science and Artificial Intelligence Laboratory
Today an application developer using a distributed hash table (DHT)
with n nodes must choose a DHT protocol from the spectrum between
O(1) lookup protocols and O(logn)
protocols. O(1) protocols achieve low latency lookups on small
or low-churn networks because lookups take only a few hops, but incur
high maintenance traffic on large or high-churn networks. O(logn)
protocols incur less maintenance traffic on large or high-churn
networks but require more lookup hops in small networks. Accordion is a
new routing protocol that does not force the developer to make this
choice: Accordion adjusts itself to provide the best performance across
a range of network sizes and churn rates while staying within a
bounded bandwidth budget.
The key challenges in the design of Accordion are the algorithms that
choose the routing table's size and content. Each Accordion node learns
of new neighbors opportunistically, in a way that causes the density
of its neighbors to be inversely proportional to their distance in ID
space from the node. This distribution allows Accordion to vary the
table size along a continuum while still guaranteeing at most O(logn) lookup hops. The user-specified bandwidth budget controls the
rate at which a node learns about new neighbors. Each node limits its
routing table size by evicting neighbors that it judges likely to have
failed. High churn (i.e., short node lifetimes) leads to a high
eviction rate. The equilibrium between the learning and eviction
processes determines the table size.
Simulations show that Accordion maintains an efficient lookup latency versus
bandwidth tradeoff over a wider range of operating conditions
than existing DHTs.
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