الفهرس 
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Abstract
Concurrency control in database management systems
has been a major focus of research in the past years.
Concurrency control is applied to permit concurrent
transaction-processing while still assuring
database
consistency. The basic approaches to concurrency control
are Two-Phase Locking (2PL). Timestamp Ordering (T/O).
and Certification (or Commit-Time Validation (CTV».
Numerous
variations of these algorithms have
been
proposed and algorithm correctness work has achieved a
degree of mathematical maturity. Due to the complexity of
the issues affecting the performance of concurrency
control algorithms. simulation is often resorted to as
the means for performance evaluation. Several attempts.
however. have been made to make use of analytical methods
for this purpose.
Most existing performance studies of concurrency
control algorithms use different approaches and make
assumptions. However. a successful attempt
a unified approach has been carried out by Y.C.
Tay’s analytic approach is based on a flow diagram
a set of equations derived using only the steady