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).
Figure: Wait-die Scheme of Deadlock prevention