An operation X upon an object o causes o to invoke an operation upon another object o?. It is now
proposed to replicate o but not o?. Explain the difficulty that this raises concerning invocations
upon o?, and suggest a solution.
What will be an ideal response?
The danger is that all replicas of o will issue invocations upon o?, when only one should take place. This is
incorrect unless the invocation upon o? is idempotent and all replicas issue the same invocation.
One solution is for the replicas of o to be provided with smart, replication-aware proxies to o?. The smart
proxies run a consensus algorithm to assign a unique identifier to each invocation and to assign one of them to
handle the invocation. Only that smart proxy forwards the invocation request; the others wait for it to multicast
the response to them, and pass the results back to their replica.
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