[GitHub] [ratis] drriguz commented on pull request #709: RATIS-1642. Specify the thread-safety requirement in StateMachine.

[GitBox <gi...@apache.org>]

drriguz commented on PR #709:
URL: https://github.com/apache/ratis/pull/709#issuecomment-1217340523

   +1 Change looks good,
   Just one suggestion, may be not related to this issue itself:
   
   Can we clarify what happens when `applyTransaction` failed?  
   See the modifications below(marked with `+`), which is copied from your reply from the mail list: 
   ```
     /**
      * Apply a committed log entry to the state machine. This method is called sequentially in
      * strict serial order that the transactions have been committed in the log. Note that this
      * method, which returns a future, is asynchronous. The state machine implementation may
      * choose to apply the log entries in parallel. In that case, the order of applying entries to
      * state machine could possibly be different from the log commit order.
      *  +
      *  + The implementation should be deterministic so that the log can be replayed in any machine,
      *  + Note that, if there are three or more servers, 
      *  + the Raft algorithm makes sure the log remains consistent even if there are hardware errors 
      *  + in one machine (or less then the majority number of machines).
      *  +
      *  + Any exception thrown in this method will be treated as unrecoverable error(such as hardware error),
      *  + and the server will be force shut down when it occurs. 
      *  + Admin should manually fix the underlying problem and then restart the machine.
   
      * @param trx the transaction state including the log entry that has been committed to a quorum
      *            of the raft peers
      */
     CompletableFuture<Message> applyTransaction(TransactionContext trx);
   ```


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