In a database, the precise and secure management of data is essential, particularly when numerous users or systems access and alter data concurrently. Lacking appropriate oversight, simultaneous reads, writes, or modifications can result in mistakes and disputes. This is where transactions become indispensable. A transaction within a DBMS guarantees that a series of operations is performed entirely or not at all, maintaining data integrity. This ensures dependable outcomes even when multiple operations transpire at once. In this article, you will discover what transactions are in a DBMS, their functioning, the various operations and states involved, and the categories of transaction schedules.

Table of Contents:

• What is a Transaction in DBMS?
• Properties of Transactions in DBMS
• Operations in a Transaction in DBMS
• Transaction Management in DBMS
• Transaction States in DBMS
• Transaction Schedules in DBMS
• Common Transaction Problems in DBMS
• Practical Applications of Transaction in DBMS
• Conclusion

What is a Transaction in DBMS?

When utilizing a Database Management System (DBMS), it is vital to handle data with precision and security. Even minor errors can lead to significant issues such as incorrect balances, absent data, or data loss. To address this concern, the notion of a transaction is employed. A transaction is an assemblage of one or more operations—like reading, updating, or deleting data—that are regarded as a unified logical entity. The primary objective of a transaction is to maintain the consistency and accuracy of the database, even during unforeseen events like power outages or system failures. If all operations within a transaction succeed, the transaction is committed, meaning the alterations are permanently saved. Conversely, if any operation encounters a problem, the transaction is rolled back to reverse all changes and safeguard the database from inaccuracies.

For instance:

When you transfer funds from your bank account to your friend’s account, the involved actions would comprise:

• Subtracting money from your bank account.
• Adding money to your friend’s account.

All these actions must occur as a unified transaction. Should any action fail, then the entire transaction must be rolled back.

Properties of Transactions in DBMS

Transactions in a Database Management System (DBMS) are defined by rules that facilitate integrity, accuracy, and data security within the database, even amid failures and when transactions are processed concurrently by various users.

These rules are known as ACID properties, which represent:

• A: Atomicity
• C: Consistency
• I: Isolation
• D: Durability

Let’s delve into each property with an example:

1. Atomicity

Atomicity refers to a transaction’s quality of functioning as a single, indivisible unit. All operations must be executed, or none at all.

Essential concept: No partial updates permitted.

Example: Imagine you are transferring funds from your account to your friend’s account.

• The bank deducts Rs 500 from your account.
• The bank credits Rs 500 to your friend’s account.

If Rs 500 is deducted from your account but the second step fails, the entire transaction must be reversed. This illustrates atomicity: either both steps are successful, or neither is.

2. Consistency

Consistency guarantees that all established rules, constraints, and data integrity conditions are upheld before and after a transaction occurs in the database. It ensures that the database transitions from one valid state to another.

Essential concept: A transaction must transition the database from one consistent state to another.

Example: Suppose there is a rule that the price of a car in inventory cannot be less than Rs 1 Lakh. If a transaction alters the price of a car to Rs 80,000, the rule is violated, rendering the database inconsistent.

3. Isolation

Isolation guarantees that concurrent transactions do not interfere with one another. Each transaction operates as if it were executing in isolation. This prevents complications like dirty reads and non-repeatable reads.

Essential concept: One transaction should not affect another transaction running concurrently.

Example: Two individuals are attempting to purchase the last car available at the same time.

• Transaction A checks the inventory (1 car available).
• Transaction B also checks the inventory (1 car available).

If both transactions are permitted to proceed, they could exceed the available stock. Isolation ensures that only one transaction is executed, while the other either waits or fails, thus preventing concurrency issues.

4. Durability

Durability signifies that once a transaction is completed successfully and committed, its outcome is permanently retained in the system, even if there is a crash.

Key point: Once successful, changes cannot be lost.

Example: Following a successful car sale, the database updates the inventory and commits. If the car selling application unexpectedly stops, upon restarting the system after shutdown, the stock updates should still be intact.

Operations in a Transaction in DBMS

In a DBMS, a transaction comprises a series of actions that are designed to execute collectively, for instance, to facilitate a money transfer. Every operation within the transaction must be conducted in a regulated manner to ensure consistency.

Generally, four actions can be found in most transactions.

To illustrate these operations, we will create a table called Cars that will serve as an example.

-- Creating the table
CREATE TABLE Cars (
  car_id INT PRIMARY KEY,
  car_model VARCHAR(50),
  price INT,
  stock INT
);
-- Inserting data
INSERT INTO Cars (car_id, car_model, price, stock) VALUES
(101, 'Honda City', 1200000, 5),
(102, 'Hyundai Creta', 1500000, 3),
(103, 'Tata Nexon', 1100000, 4);
-- Displaying the result
SELECT * FROM Cars;

Output:

This illustrates what the table looks like after its creation and data insertion.

1. Read(X) Operation in DBMS Transaction

This action fetches the current value of a data item X from the database and stores it in main memory (buffer) temporarily. The database remains unchanged with this read action.

Example: Check the price and stock of the Honda City.

SELECT price, stock FROM Cars WHERE car_model = 'Honda City';

Output:

Explanation: The query pulls all information regarding the Honda City car model.

2. Write(X) Operation in DBMS Transaction

This function alters the value of a data item X in the database. The adjusted value is saved in the main memory and then written back to the database, becoming the new value for that data item. This function is often referred to as the update operation.

Example: One unit of Tata Nexon is sold, and we need to adjust the stock by decrementing it by 1.

-- The stock of Nexon before one unit was sold
SELECT stock FROM Cars WHERE car_model = 'Tata Nexon';
-- Update the stock after the sale
UPDATE Cars SET stock = stock - 1 WHERE car_model = 'Tata Nexon';
-- The stock of Nexon after one unit is sold
SELECT stock FROM Cars WHERE car_model = 'Tata Nexon';

Output:

Explanation: This query checks the stock of the Tata Nexon prior to and following the sale of one unit.

3. Commit Operation in DBMS Transaction

The commit operation signifies the moment when the outcomes of all actions on the database become permanent. Once a transaction is finalized and committed, it cannot be reversed by rolling it back. This indicates the successful conclusion of the transaction.

Example: COMMIT is utilized to permanently save changes if the stock was updated successfully.

-- Use to make changes permanent
COMMIT;
-- Displaying the result
SELECT * FROM Cars;

Output:

Explanation: This query is implemented to ensure the changes are permanent.

4. Rollback Operation in DBMS Transaction

The ROLLBACK operation reverses modifications made during a transaction that has yet to be committed.

To effectively apply ROLLBACK, you must:

• Explicitly initiate a transaction.
• Then carry out your update within the transaction.
• And finally, ROLLBACK if required.

Example: Accidentally decreasing the stock of the Hyundai Creta.

-- Start the transaction
START TRANSACTION;
-- Mistaken update
UPDATE Cars SET stock = stock - 1 WHERE car_model = 'Hyundai Creta';
-- Realize the mistake and undo it
ROLLBACK;
-- Display the result
SELECT* FROM Cars;

Output:

Explanation: Here, the ROLLBACK operation is applied to negate the changes made by error.

Transaction Management in DBMS

Transaction management in DBMS incorporates a sequence of actions (a transaction) performed to maintain database accuracy and security. A transaction can be perceived as a singular operation. For instance, in transferring money between bank accounts, there are two fundamental actions: you deduct funds from one account and then credit them to another.

Benefits of Transaction Management in DBMS

Let’s examine how transaction management aids in ensuring database operations are dependable, consistent, and secure.

1. Data Consistency: Database management systems (DBMS) ensure that the database transitions between correct states, irrespective of simultaneous operations or concurrent users.
2. Error Recovery & Handling: A DBMS can restore the database state if a transaction encounters a failure, allowing for the retraction of any incomplete alterations if the system crashes. This error management ensures the integrity of the database remains unblemished.
3. Concurrency Control: A DBMS provides concurrency management, allowing multiple users to work simultaneously while safeguarding their transactions.
4. Simplified Application Logic: The DBMS permits developers to “group” actions for treating them as a unit of work, thus making the code more understandable, maintainable, and manageable.
5. Secure and Reliable Operations: A DBMS safeguards the data from incomplete updates, unintended alterations, or unauthorized access, ensuring that…
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6. you can verify that the details are accurate and trustworthy.

States of Transactions in DBMS

In database management systems, a transaction represents a logical unit of work consisting of one or several database operations such as insertions, updates, or deletions. It ensures that all operations are completed successfully or none at all (atomicity). Transactions guarantee that data remains stable, even during failures or crashes. Transactions adhere to ACID principles: Atomicity, Consistency, Isolation, and Durability.

State	Description
Active	This active state indicates that the transaction has been initiated and is currently executing its operations.
Partially Committed	The partially committed state signifies that all operations have been performed and are prepared to be saved (committed).
Committed	The committed state denotes that the changes have been permanently recorded in the database.
Failed	This failed state signifies that an issue has arisen, preventing the transaction from proceeding.
Aborted	The aborted state indicates that the transaction has been halted and reverted to its initial state.

Transaction Schedules in DBMS

A Database Management System (DBMS) can facilitate simultaneous operations, involving the execution of multiple transactions at the same time. This concurrent execution follows a specific order, referred to as a schedule. A transaction schedule is utilized to govern the concurrent execution of transactions, ensuring both efficiency and data accuracy.

Importance of Transaction Schedules:

• To oversee the concurrent execution of transactions.
• To minimize conflicts such as lost updates or dirty reads.
• To guarantee that the database’s final state is legitimate.
• To uphold data consistency and isolation.

Let’s examine the different types of schedules utilized in DBMS.

1. Serial Schedule

• Transactions are executed one after another.
• No interleaving of operations is allowed.
• Clear and secure. No interactions occur between transactions.
• Always ensures data consistency.

2. Non-Serial Schedule

• Interleaved operations of multiple transactions.
• Enhances system efficiency, increases resource utilization.
• May lead to inconsistencies if not managed properly.
• Additional checks must be implemented to ensure accuracy.

3. Serializable Schedule

• A serializable schedule is a non-serial schedule that produces results equivalent to a serial schedule.
• It permits concurrent execution while ensuring the database remains valid.
• Serializable schedules are crucial in multi-user settings to guarantee accurate and consistent results when transactions execute simultaneously.

Common Transaction Issues in DBMS

Transaction issues refer to the complications that arise in a DBMS when numerous transactions are conducted simultaneously. These issues stem from improper management of concurrent transactions, potentially leading to data inconsistencies. Common transaction issues include lost updates, dirty reads, and non-repeatable reads.

1. Dirty Read: A dirty read occurs when one transaction accesses data that is being modified by another transaction that hasn’t been committed yet. If the other transaction rolls back, the read data becomes invalid.

2. Lost Update: A lost update transpires when two transactions read the same data, and both subsequently update it. One of the updates is lost when it gets overwritten.

3. Uncommitted Dependency: Uncommitted dependency occurs when a transaction is allowed to read data from another transaction that has not yet been committed.

4. Inconsistent Retrievals: Inconsistent retrieval happens when a transaction reads related data from different locations, but another transaction updates part of the referenced data between queries, resulting in inconsistencies.

Practical Uses of Transactions in DBMS

1. Online Banking

An illustration of a transaction in an online banking service is when a user transfers money from their checking account to the recipient’s account.

Steps involved:

• Check the balance of the sender’s account.
• Deduct the amount the user intends to send from the sender’s account.
• Add the transferred amount to the recipient’s account.
• All modifications are saved (Commit).

2. E-commerce Order Processing

When a customer places an order on an e-commerce platform, multiple actions such as verifying inventory, processing payment, and updating the order status must be performed as a single transaction to maintain data accuracy.

Steps involved:

• Verify if the product is available.
• Reduce the quantity of items in the inventory.
• Store the order details.
• Process the payment.
• Confirm the order with the customer.

Conclusion

In a DBMS, transactions ensure that database operations are executed safely and completely. By treating multiple actions as a single unit, transactions maintain the accuracy, consistency, and reliability of data. The DBMS oversees transaction phases, rules, actions, and sequences to ensure everything operates correctly. When transaction mechanisms conform to ACID principles, the DBMS can securely manage your data, even amid unexpected failures or when multiple users modify data concurrently.

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Transactions in DBMS – FAQs

The article Transaction in DBMS was first published on Intellipaat Blog.

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