Failure Detection and Consensus in the Crash-Recovery Model
In the Crash-Recovery Model, nodes may crash infinitely, detectors may make mistakes, and stable storage plays a key role. Consensus resolution in the presence of unstable and bad nodes is discussed, highlighting scenarios where stable storage is essential. The results shed light on the complexities of achieving consensus in distributed systems.
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Presentation Transcript
Failure Detection and Consensus in the Crash-Recovery Model
System Asynchronous Message loss Nodes may crash infinitely many times Detectors may make mistakes
Definitions Unstable Nodes - may crash and recover forever Bad Nodes - are unstable or crash permanently Good Nodes - are those that never crash or eventually remain up Stable Storage - part of memory kept after crash
Some results If the number of up processes is less than the number of bad then consensus cannot be solved without stable storage even using the eventually perfect failure detector If the number of up processes is greater than the number of bad then consensus can be solved without stable storage using their simple failure detector
Some results If the number of up processes is less than the number of bad processes consensus cannot be solved without stable storage even in systems where there are no unstable processes and links do not lose messages Assume that each process can use stable storage only for storing and retrieving its proposed and decision values. If up bad and bad > 2 then consensus cannot be solved even in systems where there are no unstable processes and links do not lose messages
