Describe a serial validation, optimistic concurrency control that uses backward validation and in addition uses timestamps to distinguish the order in which conflicting read and write operations occur. The validation condition in that case need not be conservative, and only conflicts that would violate commit order cause aborts.

Question

What will be an ideal response?

Answer 1

The concurrency control assigns a unique timestamp to each transaction, T, w hen it
enters its validation phase. Then when T writes an item during its write phase, the
value of T’s timestamp is stored with that item in the database and also stored with
the information the concurrency control maintains about T’s write set to perform
validation of other transactions. The validation is then performed as follows: When a
transaction, T1, reads an item during its read phase, the control remembers the value
of that item’s timestamp. Later when T1 enters its validation phase, the control checks
if any other transaction, T2, that committed during T1’s read phase wrote any item
that T1 read. If so, it checks the timestamp of that item to see if T2 changed the value
of that item after T1 read it. If the item’s timestamp had been changed, T1 is aborted.
If there is no such item for which the timestamp has been changed, T1 is allowed to
commit.