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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