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Adaptive Concurrency Control Scheme for Transaction Processing

IP.com Disclosure Number: IPCOM000119558D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 99K

Publishing Venue

IBM

Related People

Franaszek, PA: AUTHOR [+3]

Abstract

Disclosed is an adaptive two-phase concurrency control method based on processor utilization (UCPU) which maximizes system throughput at a given degree of concurrency. At low UCPU the system runs in optimistic mode. It switches to running priority (in the first phase) when UCPU approaches one. Similarly the system switches to more and more conservative methods as the processors become saturated for the previous method.

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This is the abbreviated version, containing approximately 52% of the total text.

Adaptive Concurrency Control Scheme for Transaction Processing

      Disclosed is an adaptive two-phase concurrency control
method based on processor utilization (UCPU) which maximizes system
throughput at a given degree of concurrency.  At low UCPU the system
runs in optimistic mode.  It switches to running priority (in the
first phase) when UCPU approaches one.  Similarly the system switches
to more and more conservative methods as the processors become
saturated for the previous method.

      A family of two-phase processing methods has been described
(1), to reduce lock contention.  Since the processing in the first
phase is considered to be wasted in (1), the percentage of wasted
processing is quite high when all transactions have to be executed
twice.  An obvious improvement over this method is to use an
optimistic method in the first phase.  The optimistic method becomes
undesirable however when the system processors become saturated,
since wasted work is carried out at the expense of potential useful
work.  It is beneficial therefore to switch to a more "conservative"
method.

      A more conservative method is a modification of the Running
Priority (RP) method (2).  Experimentation has shown that this method
results in a reduction in wasted processing and improved performance
with respect to the two-phase optimistic method (higher attainable
throughput) under certain conditions (high degree of concurrent
transaction processing and slow processors).  However, the wasted CPU
processing can be unacceptably high such that more conservative
methods (as described here) become beneficial.

      In order to attain the maximum throughput for a given degree of
concurrency, we use a family of two-phase methods, which depend on
processor utilization.  Starting at low processor utilizations up to
the point of CPU saturation the two-phase optimistic method is used.
For an increasing transaction arrival rate and an increased degree of
concurrency (denoted by D), causing processors to reach 100%
utilization, the system switches to the two-phase RP method. As the
number of transactions in the system (D) increases further, the
system switches to more conservative methods which are variations of
the RP method as follows:  restart a transaction only if it blocks b
transactions, such that the value of b is a function of system load
(D).

      The system initially runs at a low system load (unsaturated
processors) according to a two-phase optimistic method (b equals zero
at this point).  As the...