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In update based protocols with a large number of processors, a lot of the bandwidth is occupied by the update operations since the same cache line might have to be updated on all the processors. The following 2 scenarios make the updates useless:

1) The updated value is never read again from the various processors whose cache lines were updated.

2) There are a lot of subsequent updates before the other processors read from the cache line.

The above scenarios adversely affect performance in update based protocols.