ADBMS: LOCK BASED

lock

A _____ in DBMS controls concurrent access, allowing only one

transaction to use a data item at a time. This ensures data integrity

and prevents issues like lost updates or dirty reads during

simultaneous transactions.

Lock Based Protocol

________ in DBMS ensure that a

transaction cannot read or write data until it gets the

necessary lock

Shared Lock

is also known as Read-only lock

Shared Lock

As the name suggests it can be shared between transactions because while holding this lock the transaction does not have the permission to update data on the data item

lock-S instruction.

lock S is requested using ____

Exclusive Lock

Data item can be both read as well as written. This is Exclusive and cannot be held simultaneously on the same data item.

lock-X instruction

X-lock is requested using ____

True

True / False

If a Transaction has a Read lock on a data item, it can read the item but not update it.

False

True/False

If a transaction has a Read lock on the data item, other transaction can obtain Read Lock on the data item including Write Locks.

True

True/False

If a transaction has a write Lock on a data item, it can both read and update the data item.

False

True/False

If a transaction has a write Lock on the data item, then other transactions can obtain either a Read lock or write lock on the data item.

Exclusive Lock

the Write Lock is also known as

Shared Lock

Read lock is also known as

shared locks

Multiple transactions can hold _____ on the same data item simultaneously

exclusive lock

If a transaction holds an _____ on a data item, no other transaction can hold any type of lock on that item.

Concurrency Control Protocol

are the methods used to manage

multiple transactions happening at the same time. They ensure that

transactions are executed safely without interfering with each other,

maintaining the accuracy and consistency of the database.

data conflicts, lost updates or inconsistent data

These protocols prevent issues like _____, _____ or _____by controlling how transactions access and modify data.

Simplistic Lock Protocol

Pre Claiming Lock Protocol

Two Phase Locking Protocol

Strict Two Phase Locking Protocol

Types of Lock-Based Protocols

Simplistic Locking Protocol

It is the simplest method for locking data during a transaction

Simplistic Lock Protocol / Simple Lock Based Protocol

enable all transactions to obtain a lock on the data before inserting,

deleting, or updating it. It will unlock the data item once the transaction is

completed.

Pre Claiming Lock Protocol

avoids deadlocks by requiring a

transaction to request all needed locks before it starts. It runs only if all

locks are granted; otherwise, it waits or rolls back.

Two Phase Locking Protocol

A transaction is said to follow the Two-Phase Locking protocol if Locking

and Unlocking can be done in two phases: Growing Phase and Shrinking Phase

Growing Phase

New locks on data items may be acquired but none can be released.

Shrinking Phase

Existing locks may be released but no new locks can be acquired.

Strict Two-Phase Locking

_____ requires that in addition to the 2-PL all

Exclusive(X) locks held by the transaction be released until after the

Transaction Commits.

Deadlock

both transactions are waiting for resources held by the

other, preventing either from proceeding with their execution.

Starvation

_____ is also possible if concurrency control manager is badly designed. For example: A transaction may be waiting for an X-lock on an item, while a sequence of other transactions request and are granted an S-lock on the same item. This may be avoided if the concurrency control manager is properly designed.