How to Fix Exponential Backoff

Randomized exponential backoff is a widely deployed technique for coordinating access to a shared resource. A good backoff protocol should, arguably, satisfy three natural properties: (i) it should provide constant throughput, wasting as little time as possible; (ii) it should require few failed access attempts, minimizing the amount of wasted effort; and (iii) it should be robust, continuing to work efficiently even if some of the access attempts fail for spurious reasons. Unfortunately, exponential backoff has some well-known limitations in two of these areas: it provides poor (sub-constant) throughput (in the worst case), and is not robust (to resource acquisition failures). The goal of this paper is to “fix” exponential backoff by making it scalable, particularly focusing on the case where processes arrive in an on-line, worst-case fashion. We present a relatively simple backoff protocol RE-BACKOFF that has, at its heart, a version of exponential backoff. It guarantees expected constant throughput with dynamic process arrivals and requires only an expected polylogarithmic number of access attempts per process. RE-BACKOFF is also robust to periods where the shared resource is unavailable for a period of time. If it is unavailable for D time slots, RE-BACKOFF provides the following guarantees. When the number of packets is a finite n, the average expected number of access attempts for successfully sending a packet is O(log(n+D)). In the infinite case, the average expected number of access attempts for successfully sending a packet is O(log(η) + log(D)) where η is the maximum number of processes that are ever in the system concurrently. This research was supported in part by NSF grants CCF 1114809, CCF 1217708, CCF 1218188, IIS 1247726, IIS 1251137, CNS 1408695, CCF 1439084, CNS-1318294, and CCF-1420911. ar X iv :1 40 2. 52 07 v4 [ cs .D C ] 1 2 Ju l 2 01 5