A client is the only reader and writer of a data item X. Client moves between locations L1 and L2. A server at each location has a replica of the item X which also stores X's local version number (generation). The client reads and writes are always performed locally. A read operation R also returns the local version number of the item X. The initial version number of each copy is equal to 0. A write W increments the (local) version number by 1. PW is an update operation to the remote copy (e. g. after a local W). PW carries the version number of X and stores it with the update. The "" is the time line and the time grows from left to right. For each sub-problem below write the version number next to each R, W, and PW operation and answers the questions
1) Does the sequence of operations below provide monotonic-read consistency?
Explain why it does or does not. If your answer is no, can you add an operation to the sequence so that it does provide monotonic-read consistency (and explain why it does) Use this definition: the monotonic-read consistency guarantees that if a process accessed later time. version of at time t, it will never see an older version of x at
L1 W R P
L2 PW W R.
2) Does the sequence of operations below provide monotonic-write consistency?
Explain why it does or does not. If your answer is no, can you add operations to the sequence so that it does provide monotonic-write consistency (and explain why it does). Use this definition: monotonic-write consistency guarantees that a write is executed on the value of a variable that is the result of all the previous write operations.
L1 W R P
L2 P W R W