Retaining information in the VQ about transactions that committed longer ago than the timeout period is also not useful. The result of these optimizations is a loss of precision in multistamps, which may in turn lead to more fetch stalls. When that multistamp arrives at C, C may block while waiting for invalidation information from S even though S has no invalidations for it. To handle such a situation, the timestamp in the invalidation response will be the value of the server's current clock. This situation is extremely unlikely, since it occurs only if clocks are out of synch.
Every message sent to the client contains a piggybacked invalidation message.
This timestamp allows the clients to avoid stalls.