A write of x = 2 finishes. Then a read of x starts. What must the read return?

• 1, the value from before
• 2
• Either 1 or 2

Each operation appears to take effect at one instant. Where must that instant sit?

• Between its call and its return
• Before its call
• After its return

A write of x = 1 completes, then a read of x returns 1. This history is linearizable.

Circle one:   True   False

A write of x = 1 finishes, then a write of x = 2 finishes, then a read returns 1. What is the verdict?

• Not linearizable, and the read is the conflict
• Linearizable, with the read placed last
• Linearizable, with the two writes swapped

A write of x = 1 and a write of x = 2 overlap in time. A concurrent read returns 1. Is there a single-object explanation?

• No, overlapping writes never allow one
• No, the read would have to return 2
• Yes, the read can sit before both writes

The clients and the server log disagree about which operation ran first. What decides the check?

• The order the server executed them
• Whichever order makes the history valid
• The client call and return times

Write A finishes. Then write B overlaps a read that returns B. Which single-object order explains it?

• B, then A, with the read beside B
• A, then B, with the read before A
• A, then B, with the read beside B

Sam says a history is fine because the server ran the read before the write. The client saw the write finish first. What is wrong?

• Reads always outrank writes
• Server order never decides, client windows do
• Overlapping operations are forbidden