Pessimistic concurrency control protocols in real-time database

Pessimistic concurrency control protocols in real-time database, real-time database versions of 2PL protocols

Pessimistic Concurrency Control Protocols (Lock based protocols)

In conventional database systems, Two Phase Locking (famously known as 2PL) protocol is the popular protocol to handle concurrent execution of transactions using locks (shared locks for reading, and exclusive locks for writing).

In real-time database, the transactions have to be handled in a timely manner. But in conventional database the things like other executing transactions, the mode in which we access a data item, the availability of CPU or I/O, etc. makes it hard to realize the deadlines.

Hence, we need changes in the conventional 2PL to incorporate priorities. In a real-time database, it is undesirable for a higher priority transaction to be blocked by lower priority transactions. This is called priority inversion, and it has to be overcome. Here, we shall discuss about various such protocols extended from 2PL as proposed by researchers.

They are;

• 2PL Wait-Promote (2PL-WP)

• 2PL High-Priority (2PL-HP)

• Priority Ceiling Protocol (PCP)

• Conditional Priority Inheritance (CPI)

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