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==== Safety rules in Raft ====
Raft guarantees each of these safety properties
* '''Election safety:''' at most one leader can be elected in a given term.
* '''Leader append-only:''' a leader can only append new entries to its logs (it can neither overwrite nor delete entries).
* '''Log matching:''' if two logs contain an entry with the same index and term, then the logs are identical in all entries up through the given index.
* '''Leader completeness:''' if a log entry is committed in a given term then it will be present in the logs of the leaders since this term.
* '''State machine safety:''' if a server has applied a particular log entry to its state machine, then no other server may apply a different command for the same log.
The first four rules are guaranteed by the details of the algorithm described in the previous section. The State Machine Safety is guaranteed by a restriction on the election process.
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