What is ACID transactions?

ACID transactions are a fundamental concept in database systems, ensuring data integrity and consistency. The acronym stands for Atomicity, Consistency, Isolation, and Durability. These principles guarantee that all database transactions are processed reliably, even in the event of system failures, making them crucial for robust and secure data management


Jatin Solanki

Updated on

June 15, 2024

What is ACID Transaction?

ACID is not about chemistry or science experiments—it stands for Atomicity, Consistency, Isolation, and Durability. These four principles are like the superheroes of data management, working together to ensure that data is handled carefully and reliably in databases. They act as a shield that protects our valuable information from getting lost, damaged, or corrupted.

But why are ACID transactions important? Imagine you have an important project saved on your computer, and suddenly, the power goes out. With ACID transactions, your project might get better, and all your hard work could be recovered. ACID transactions come to the rescue, making sure that even if something unexpected happens, your project remains safe and intact.

In today’s blog, let us dive deeper into each ACID principle to understand how they work their magic to keep our data secure and reliable. 

Understanding the ACID Principles:

Now that we know ACID stands for Atomicity, Consistency, Isolation, and Durability, let's take a closer look at each of these.

Atomicity: In ACID transactions, atomicity ensures that all the actions or changes we make to the data happen as a complete unit. If any part of the transaction fails, the whole thing is undone. This helps keep our data consistent and avoids any partial or incomplete changes.

Consistency: When we perform a transaction, it has to follow rules and constraints set by the database. If a transaction violates any rules, it's like breaking the team's code of conduct, and the transaction is not allowed. Consistency makes sure our data is always accurate and dependable.

Isolation: In ACID transactions, isolation ensures that different transactions happening at the same time don't mess up each other's data. Isolation helps prevent conflicts and ensures that the transactions are independent of one another. This way, each transaction can focus on its task without causing problems for others.

Durability: Durability guarantees that once a transaction is done, the changes made to the data are permanent and won't get lost, no matter what happens. It's like creating an unbreakable shield around our data. Even if there's a power outage or a computer crash, the changes made during a transaction are saved and can be recovered. Durability ensures the long-term safety and availability of our data.

By combining these four superpowers, ACID transactions provide a solid foundation for data management. They ensure that our data is protected, consistent, isolated, and durable. Whether it is a simple task like adding a friend's name to a contact list or a complex operation like processing thousands of online orders, ACID transactions ensure that our data remains safe and reliable.

Now that we've explored the basics of ACID transactions, let's delve deeper into each principle and discover how they work in real-life scenarios. 

Exploring Atomicity in ACID Transactions:

Imagine you're transferring money from your savings account to your piggy bank. This transaction involves two actions: subtracting the money from your savings account and adding it to your piggy bank. With atomicity, both actions occur together. If, for some reason, one action fails, like if the piggy bank is full, the entire transaction is rolled back, and the money remains in your savings account. It's as if the transfer never happened, and you don't lose any money.

Atomicity ensures that we don't end up with a half-finished or partially updated state. To achieve atomicity, ACID transactions use various techniques, such as 

-transactional units

Transactional units divide complex operations into smaller, manageable steps, ensuring that each step is completed successfully before moving to the next.


If any step fails, the transaction can be rolled back, undoing the changes made so far. 

-recovery mechanisms. 

Recovery mechanisms, like logging and undo/redo logs, help track and restore the state of the transaction in case of failures.

Maintaining Consistency with ACID Transactions:

In ACID transactions, consistency ensures that our data stays in a good and reliable state. It is like having a team working together to maintain order and prevent any chaos. Let's understand how consistency works using a relatable example.

Imagine you have a list of friends' names, and you want to add a new name to the list. However, there's a rule that says no two names can be the same. Consistency steps in to enforce this rule. When you add a new name, consistency checks if it violates any rules or constraints. If the new name is already on the list, consistency blocks the transaction, just like a superhero stopping a villain from breaking the rules. This ensures that our data remains consistent and follows the predefined guidelines.

Consistency also plays a vital role in handling complex operations involving multiple actions. Let's say you're booking a flight ticket online. The transaction involves deducting money from your account, reserving a seat, and sending you a confirmation email. Consistency ensures that all these actions happen correctly and in the right order. If any step fails, consistency rolls back the entire transaction, like rewinding time, ensuring that no half-completed or inconsistent changes are made.

To maintain consistency, ACID transactions use techniques like 

- data validation

Data validation checks, if the data is entered or modified, and meets specific criteria or rules.

- constraint enforcement. 

Constraint enforcement sets rules and restrictions on the data, preventing any violations. For example, a constraint might enforce that a date cannot be in the future or that a field cannot be left blank.

By upholding consistency, ACID transactions ensure that our data remains accurate, reliable, and trustworthy. 

Achieving Isolation in ACID Transactions:

In ACID transactions, isolation ensures that different transactions happening at the same time don't mess up each other's data. It's like carrying out individual activities without getting in each other's way.

Imagine two individuals wanting to buy something from a store. You go to the store together, but you each handle your transaction independently. Isolation ensures that while you are selecting your purchase and making the payment, the other individual’s transaction is completely separate and doesn't affect yours.

Isolation prevents data conflicts that can arise when multiple transactions try to access or modify the same data simultaneously. It ensures that each transaction behaves as if it's the only one running, even though there may be many others happening at the same time. This way, we avoid situations where one transaction interferes with or alters the data of another transaction.

To achieve isolation, ACID transactions use techniques like 

- locking 

Locking is like having a special key that allows only one transaction to access a particular piece of data at a time.  If one transaction holds a lock on a piece of data, other transactions have to wait their turn. This prevents conflicts and ensures that each transaction can work on the data without any interference.

- concurrency control.

Concurrency control techniques manage how transactions interact with each other. They ensure that transactions don't step on each other's toes and that changes made by one transaction become visible to others only when they're ready.

By achieving isolation, ACID transactions provide a safe and secure environment for our data. Each transaction can perform its tasks independently, without worrying about conflicts or disruptions caused by other transactions. Isolation allows us to trust that our data remains consistent and accurate, even when many transactions are happening simultaneously.

Ensuring Durability in ACID Transactions:

In ACID transactions, durability ensures that once a transaction is committed and completed, its changes are permanent and can withstand any unexpected events or failures.

Imagine an artist drawing a beautiful picture. Once done, he wants to make sure that the artwork is preserved forever. Durability ensures that even if something happens to the original drawing like it gets accidentally smudged or torn, you have a backup copy or a way to restore it.

Durability is achieved through various techniques and mechanisms. One such technique is 

- write-ahead logging.

It's like keeping a detailed record of every change made during a transaction in a special logbook. This logbook acts as a safety net, allowing us to recover the data in case of any failures or crashes. If something goes wrong, we can refer to the logbook and restore the data to its last known good state.

Another technique used for durability is 

- data replication. 

Data replication ensures that the changes made during a transaction are replicated or duplicated in multiple locations, providing redundancy and safeguarding against data loss.

Durability is a critical aspect of ACID transactions because it ensures that our data remains resilient and recoverable.

ACID vs. Non-ACID Transactions:

In the world of data management, there are two types of transactions: ACID and non-ACID. ACID transactions are like superheroes with incredible powers, while non-ACID transactions are more like regular individuals without any extraordinary abilities. Let's explore the differences between them and understand why ACID transactions reign supreme.

  1. Reliability: ACID transactions are known for their reliability and robustness. They guarantee that the data will remain consistent and recoverable even if something goes wrong during a transaction, like a system crash or a power outage. On the other hand, non-ACID transactions lack this level of reliability and may leave the data in an inconsistent or incomplete state if a failure occurs.
  2. Consistency: ACID transactions ensure data consistency by enforcing rules and constraints. They make sure that the data remains in a valid and predictable state throughout the transaction. Non-ACID transactions, however, may not have mechanisms in place to maintain consistency, which can lead to data integrity issues and conflicts.
  3. Isolation: ACID transactions provide isolation, which means that multiple transactions can run concurrently without interfering with each other. Each transaction is like a separate bubble, keeping its data isolated and protected from other transactions. Non-ACID transactions, on the other hand, lack isolation and may result in data conflicts or inconsistencies when multiple transactions access and modify the same data simultaneously.
  4. Durability: ACID transactions ensure durability by guaranteeing that once a transaction is committed, its changes are permanent and recoverable, even in the event of failures. Non-ACID transactions may not provide the same level of durability, which can lead to data loss or unrecoverable changes in case of system crashes or other unexpected incidents.

ACID transactions, with their superpowers of reliability, consistency, isolation, and durability, offer a solid foundation for managing critical data and ensuring its integrity. They act as superheroes that protect our data and maintain order in the complex world of database management.

Non-ACID transactions, although lacking in these superheroic abilities, can still be useful in certain scenarios where strict data consistency or durability is not a primary concern. They may provide performance advantages in certain situations where speed is prioritized over data integrity.

Embracing the Superpowers of ACID Transactions for Reliable Data Management:

While non-ACID transactions may have their uses in specific scenarios where strict consistency or durability is not a priority, ACID transactions remain the go-to choice for ensuring the reliability and accuracy of our data.

By understanding the principles and powers of ACID transactions, we can make informed decisions when designing and implementing data management systems. ACID transactions provide us with the confidence that our data will remain consistent, secure, and recoverable, even in the face of challenges.

So, embrace the superheroic abilities of ACID transactions and let them empower your data management endeavors. With ACID transactions by your side, you can ensure the integrity and reliability of your valuable information.

External Links:

  1. Databricks: Learn about ACID transactions
  2. MongoDB:
  3. Devopedia
  4. Keboola
  5. Wikipedia
  6. Dremio
  7. Atomicity (database systems) - Wikipedia

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