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A client reserves sequence numbers for RPC ids. It reserves M+1 consecutive ids, where M is the number of objects involved in the current transaction. The lowest seq# is not assigned to any object or RPC and work as placeholder. Other M sequence numbers are assigned to each object.
RPC (1) PREPARE: A client sends prepare messages to all data master servers participating transaction. For understandability, we send a separate RPC request for each object in transaction.
1. Request msg: <list of <tableId, keyHash, Seq#>, tableId, key, condition, newVal>
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1. 1. 1. list of <tableId, keyHash, Seq#>: used in case of client disconnection.
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1. 1. 1. TableId & Key: object operating on.
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1. 1. 1. Condition: condition for COMMIT-VOTE other than successful locking. RAMCloud RejectRules. This can be NULL.
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1. 1. 1. newVal: value to be written for “key” on the receipt of “COMMIT”.
  2. Handling:
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  1. 1. 1. Grab a lock for “key” on lock table. Buffer newVal for the key.
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  1. 1. 1. - If the lock was grabbed & condition is satisfied, log LockRecord (lock information. See figure~\ref{fig:lockRecord}) and RpcRecord (linearizability. See figure~\ref{fig:rpcRecord})
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  1. 1. 1. If grabbed the lock but condition is not satisfied, unlock immediately, and log RpcRecord with the result of “ABORT-VOTE”
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  1. 1. 1. If we failed to grab the lock, log RpcRecord with the result of “ABORT-VOTE”.
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  1. 1. 1. Sync log with backup.
    2. Response: either “COMMIT-VOTE” or “ABORT-VOTE”.
  2. RPC(3) DECISION: After collecting all votes from data masters, the client broadcast its decision to all cohorts.
    1. Request: <tableId, keyHash, seq# for PREPARE, DECISION>
    2. Handling: if DECISION = COMMIT,
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    1. 1. If there is a buffered write, log Object (with new value), Tombstone for old Object, and Tombstone for LockRecord atomically.
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    1. 1. Unlock the object in lock table.
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    1. 1. Sync log with backup…? Is it safe on master crash?
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    1. 1. (It is okay to delay sync until we sync a next transaction’s LockRecord. We only need a guarantee that only one LockRecord exists per object.)
      2. Response: Done.
    2. After collecting “Done” from all cohorts, the client acknowledge the lowest seq# reserved, so that ACK# can reach up to the highest seq# used in this transaction.
    Discussions & Questions:
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