Causal consistency stipulates that causally dependent writes to data items should be executed in causal order. Traditionally this has been done by causally ordered message delivery using vector clocks. In a vector clock of size N, each element of the vector corresponds to each of the N hosts in the system and hence the message overhead is Θ(
N
). In a mobile environment the number of hosts can not be fixed because hosts join and leave the system dynamically. Hence traditional vector clocks are not suitable in a mobile environment. Consistency of a system consisting of M data items can be maintained using a vector in which each element corresponds to each data item. We propose a mechanism for maintaining causal consistency whose message overhead is Θ(
M
). Such a model will be advantageous in a mobile environment, because the message overhead is independent of the number of hosts. Further in applications such as collaboration the number of data items is small. Also, the delivery of a message is never inhibited due to causally overwritten messages.
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