Title:
Space-Efficient Atomic Snapshots in Synchronous Systems
Space-Efficient Atomic Snapshots in Synchronous Systems
Authors
Neiger, Gil
Singh, Ranu
Singh, Ranu
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Abstract
We consider the problem of implementing an atomic snapshot memory in
synchronous distributed systems. An atomic snapshot memory is an array
of memory locations, one per processor. Each processor may update its
own location or scan all locations atomically. We are interested in
implementations that are space-efficient in the sense that they are
honest. This means that the implementation may use no more shared
memory than that of the array being implemented and that the memory
truly reflect the contents of that array. If n is the number of
processors involved, then the worst-case scanning time must be at least
n. We show that the sum of the worst-case update and scanning times
must be greater than floor(3n/2). We exhibit two honest
implementations. One has scans and updates with worst-case times of
n+1 for both operations; for scans, this is near the lower bound. The
other requires longer scans (with worst-case time ceiling(3n/2)+1) but
shorter updates (with worst-case time ceiling(n/2)+1). Thus, both
implementations have the sum of the worst-case times at 2n + O(1),
which is within n/2 of the lower bound. Closing the gap between these
algorithms and the combined lower bound remains an open problem.
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Date Issued
1993
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185818 bytes
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Text
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Technical Report