A quorum is the minimum number of votes that a distributed
transaction has to obtain in order to be allowed to perform an operation
in a distributed scenario. A quorum-based technique is implemented to enforce consistent operation in a distributed system.
Typically mutual exclusion is sought to avoid conflict and in distributed system this becomes a rather complex job. Timestamps, Token-based algorithms are the other ways of doing the same, but they are vulnerable to failures, whereas quorum based algorithms don't have single point of failure. In the timestamps based algorithm, the process seeks permissions from all other participating processes to enter a critical section. In the token based algorithm the permission is required from one process. The quorum based algorithm, however, seeks permission from a subset of processes called request set.
There are three metrics to compare various quorum systems;
Typically mutual exclusion is sought to avoid conflict and in distributed system this becomes a rather complex job. Timestamps, Token-based algorithms are the other ways of doing the same, but they are vulnerable to failures, whereas quorum based algorithms don't have single point of failure. In the timestamps based algorithm, the process seeks permissions from all other participating processes to enter a critical section. In the token based algorithm the permission is required from one process. The quorum based algorithm, however, seeks permission from a subset of processes called request set.
There are three metrics to compare various quorum systems;
