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A Dynamo-style store versions objects with vector clocks. Four versions of one key exist.

version	clock	how it arose
D1	`[(Sx,1)]`	first write, coordinated by Sx
D2	`[(Sx,2)]`	same client updates, Sx coordinates again
D3	`[(Sx,2),(Sy,1)]`	same client updates D2, Sy coordinates
D4	`[(Sx,2),(Sz,1)]`	a different client that had read D2 updates it, Sz coordinates

A node holding D3 receives D4. What happens, and if the client then reconciles and Sx coordinates the resulting write D5, what clock does D5 carry?

The node rejects D4 and asks Sz to retry, because a write may only be coordinated by a node already present in the object's clock.

Neither descends from the other, so both are kept and returned together on the next read. After reconciliation D5 carries [(Sx,3),(Sy,1),(Sz,1)].

Neither descends from the other, so both are kept. D5 carries [(Sx,2),(Sy,1),(Sz,1)], the element-wise maximum of the two clocks.

D4 overwrites D3. Both descend from D2, and D4 was written later, so last write wins and D5 carries [(Sx,2),(Sz,1)].