Wait-die scheme -deadlock prevention, Database Management System

Wait-die" scheme: The idea is based on non-preventive method. It is based on a simple rule:

                                If Ti requests a database resource that is held by Tj

                                then if Ti has a smaller timestamp than that of Tj

                                 it is permitted to wait;

                else Ti aborts.

A timestamp may loosely be described as the system generated sequence number that is unique for every transaction. Therefore, a smaller timestamp means an older transaction. For example, suppose that 3 transactions T1, T2 and T3 were generated in that series, then if T1requests for a data item which is presently held by transaction T2, it is permitted to wait as it has a smaller time stamping than that of T1. Though, if T3 requests for a data item which is presently held by transaction T2, then T3 is rolled back (die).

                                       1541_Wait-die scheme -Deadlock prevention.png

                                                            Figure: Wait-die Scheme of Deadlock prevention

Posted Date: 3/12/2013 3:10:06 AM | Location : United States

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