Lecture 6

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Unformatted text preview: erializable, sequentially consistent: the result of any execution is the same as if the operations of all the processors were executed in some sequential order, and the operations of each individual processor appear in this sequence in the order specified by its program. Equivalent definition: operates as if there is only one copy of memory, and all memory operations are serialized Slightly stronger (linearizable): sequentially consistent, and consistent with real time [means: operates with one copy, rather than “as if” there is one copy] Sidebar: A bit of subtlety that can trip you up: we think of read and write being instantaneous, but they do take time to perform, eg., because some might need to be sent to a server. Even on a single node reads and writes take time. So: Start of write Write finishes Start of read on a different processor Value returned Suppose the start of the read might overlap the time of the write; what value should be returned? Ditto if there are two overlappin...
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This document was uploaded on 04/04/2014.

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