the space complexity of long-lived and one-shot timestamp implementations
This paper is concerned with the problem of implementing an unbounded timestamp object from multi-writer atomic registers, in an asynchronous distributed system of n processors with distinct identifiers where timestamps are taken from an arbitrary universe. Ellen, Fatourou and Ruppert [7] showed that ? n /2- O (1) registers are required for any obstruction-free implementation of long-lived timestamp systems from atomic registers (meaning processors can repeatedly get timestamps). We improve this existing lower bound in two ways. First we establish a lower bound of n /6 - O (1) registers for the obstruction-free long-lived timestamp problem. Previous such linear lower bounds were only known for constrained versions of the timestamp problem. This bound is asymptotically tight; Ellen, Fatourou and Ruppert [7] constructed a wait-free algorithm that uses n -1 registers. Second we show that ?( n )- O (1) registers are required for any obstruction-free implementation of one-shot timestamp systems (meaning each processor can get a timestamp at most once). We show that this bound is also asymptotically tight by providing a wait-free one-shot timestamp system that uses fewer than 2? n registers, thus establishing a space complexity gap between one-shot and long-lived timestamp systems.
space complexity timestamps wait-free solo-termination shared memory