That was the question I was going to ask. I don't understand any possible means that the system can resolve this issue. Traditional database systems always have one canonical value of row X at any point in time. The value can change for earlier transactions but there can never but multiple values of X for the same time. What happens as soon as client 3 comes along and wants to read row X? Making a decision is akin to choosing which transaction you will accept as valid and which you will reject!
The paper describes this scheme as READ Committed which doesn't make generally make sense except in the context of a database with secondary indexes.
The paper describes this scheme as READ Committed which doesn't make generally make sense except in the context of a database with secondary indexes.