In PostgreSQL, We can apply different lock mode on the table.
This is also one of the important topics because PostgreSQL has a default MVCC architecture.

What is Multi Version Concurrency Control (MVCC)

Because of MVCC architecture, all other sessions can access table new data or an old version of the data.
Sometimes Isolation Level like Repeatable Read, Serializable might not help us.

When we require explicitly lock on the table, we can use PostgreSQL different types of lock mode like:
ACCESS SHARE, ROW SHARE, ROW EXCLUSIVE, SHARE UPDATE EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, ACCESS EXCLUSIVE.
For highly secure tables, we require lock mode like ACCESS EXCLUSIVE MODE.

Example of ACCESS EXCLUSIVE MODE:

Create a sample table:

CREATE TABLE tbl_Employee
(
	EmpID INTEGER
	,EmpName VARCHAR(50)
);

INSERT INTO tbl_Employee
VALUES 
(1,'Anvesh'),(2,'Neevan')
,(3,'Roy'),(4,'Martin');

Apply ACCESS EXCLUSIVE MODE on tbl_Employee:

BEGIN TRANSACTION;
LOCK TABLE tbl_Employee IN ACCESS EXCLUSIVE MODE;

Open another session and,try to SELECT tbl_Employee data:
You can not access this table because ACCESS EXCLUSIVE MODE on tbl_Employee.

Now execute COMMIT to release the ACCESS EXCLUSIVE MODE and now you can access tbl_Employee in another session.

COMMIT TRANSACTION;

Note: You can apply LOCK MODE on a table only in transaction block like between BEGIN…COMMIT.

Today morning, one of our Associate DB Developer working with Transactions and PostgreSQL is also new for him.
The COMMIT, ROLLBACK and SAVEPOINT are very common for all RDBMS.

In this post, I am sharing one basic demonstration on COMMIT, ROLLBACK and SAVEPOINT of PostgreSQL which helps to Associate level DB Developer.

Create a table with Sample Data:

CREATE TABLE tbl_Employees
(
	EmpID INT
	,EmpName CHARACTER VARYING
);

INSERT INTO tbl_Employees
VALUES	
(1,'Anvesh'),(2,'Loother'),(3,'Roy'),(4,'Martin')
,(5,'Jenny'),(6,'Monika'),(7,'Rajesh'),(8,'Eric');

Commit: We can use COMMIT to end our all transactions and make It as permanent changes.

Commit the Transaction:

BEGIN;
	UPDATE tbl_Employees
	SET EmpName = 'Nivu'
	WHERE EmpID = 3;
COMMIT;

Rollback: Using ROLLBACK, we can jump to the previous last committed state of the Transaction.
Rollback the Transaction:

BEGIN;
	UPDATE tbl_Employees
	SET EmpName = 'Vinay'
	WHERE EmpID = 2;
ROLLBACK;

Savepoint: Using SAVEPOINT, we can jump to the particular point which defines by the SAVEPOINT.

Rollback changes to the Save Point:

BEGIN;
	UPDATE tbl_Employees
	SET EmpName = 'Grace'
	WHERE EmpID = 4;
	
SAVEPOINT EmpSave;

	UPDATE tbl_Employees
	SET EmpName = 'Kunal'
	WHERE EmpID = 5;
	
ROLLBACK TO EmpSave;

The Result:

SELECT * FROM tbl_Employees ORDER BY 1 ;

EmpID    EmpName
--------------------
  1      Anvesh
  2      Loother
  3      Nivu
  4      Grace
  5      Jenny
  6      Monika
  7      Rajesh
  8      Eric