Timestamp-Based Conc. Control (cont)

Rules for preserving serial order using timestamps:

a) Perform the operation X if X=READ and t>=tw or if X=WRITE, t >= tr, and t >= tw.  X=READ: set read-time to t if t > tr. X=WRITE: set write-time to t if t > tw.

b) Do nothing if X=WRITE and tr <= t < tw.

c) Abort transaction if X=READ and t < tw or X=WRITEand t < tr.

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