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The recovery subsystem of an experimental data management system is described and evaluated. The transactmn concept allows application programs to commit, abort, or partially undo their effects. The DO-UNDO-REDO protocol allows new recoverable types and operations to be added to the recovery system Apphcation programs can record data m the transaction log(More)
CONVOYS DESCRIBED When driving on a two-lane road with no passing one often encounters clusters of cars. This is because a fast-moving car will soon bump into a slow one. The equilibrium state of such a system is for everyone to be in a convoy behind the slowest car. In System R [Astrahan], transactions often bump into one another when contending for shared(More)
In the independent reference model of program behavior, King's formulas for the expected FIFO (" first-in-first-out ") and expected LRU (" least-recently-used ") miss ratios each contain an exponential number of terms (very roughly nCAP, where n is the number of pages and CAP is the capacity of main memory). Hence, under the straightforward algorithms,(More)
System R supports a high-level relational user language called SQL which may be used by ad hoc users at terminals or as an embedded data sublanguage in PL/I or COBOL. Host-language programs with embedded SQL statements are processed by the System R precompiler which replaces the SQL statements by calls to a machine-language access module. The precompilation(More)
Upper and lower bounds on processor utilization for the queueing model M/G/1/N are derived. The upper bound is equal to the utilization for constant service times and the lower bound is approached when the average number of operations per busy period approaches one. These bounds show that the form of the processing time distribution can have a substantial(More)
L L b c-We use the central server model to extend Buzen's results on balance and bottlenecks. We develop two measures which appear to be useful for evaluating and improving computer system performance. The first measure, called the balance index, is useful for balancing requests to the peripheral processors. The second quantity, called the sensitivity(More)
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