Understanding the Basics of ACID Principles in Database Management
Tags: database, architecture, performance, webdev
Published: 2023-03-20 16:26:49

During a recent interview, I was asked if I was familiar with the term "ACID" in the context of database administration or software development. While I had heard of the term before, I was uncertain of its meaning. I provided the interviewer with a brief explanation of my understanding, to which he replied “Hmm…alright”. In this article, we will delve into the ACID principle, its importance, real-world use cases, and why it is important.

Let's discuss transaction and its meaning before delving into the ACID principles and their significance.

## Transaction

In the context of a database, a "transaction” is a group of database read-and-write operations that only succeed if all the operations within them succeed. Let’s walk through a classic example to explain this concept. Imagine you made a transfer from a personal account to a work account. Two actions are to take place

1. Your account is debited (if you have enough funds to make that transfer) and your account balance is updated accordingly.
    
2. Your work account is credited with the transferred amount, and the account balance is updated accordingly.
    

These two operations have to happen, or neither will happen at all. To keep the system consistent, there cannot be an in-between state during this operation. In a basic sense, that is what a transaction is all about.

## A.C.I.D Properties of a transaction

ACID is an acronym that stands for **Atomicity**, **Consistency**, **Isolation**, and **Durability**. which refers to properties that define a transaction. These ACID properties ensure that a set of database operations leaves the database in a valid state even in the event of unexpected errors. ACID transactions guarantee that each read, write, or modification of a table has the following properties:

### Atomicity

Atomicity ensures that a transaction's operations are handled as an independent unit and will either succeed or fail together. This is important because we can be certain of the status of the database in the event of an unpredictable scenario, such as a crash or power outage. If any aspect of the transaction failed, it would have either been completed successfully or rolled back.

If we continue with the above example, if money is deducted from the account and the transaction fails, the changes are discarded and the transaction doesn't go through.

### Consistency

Consistency ensures that transactions only make predetermined, predictable modifications to tables. Transactional consistency makes sure that data corruption or mistakes don't have unintended effects on your table's integrity.

Let's go back to the earlier scenario and say you want to transfer money from your personal account to a work account once more, but your balance is negative. Even though you are aware that your account does not meet the requirements, you still attempt to make the transfer. You will be breaking the transaction's integrity, and the transaction will fail as a result.

### Isolation

Isolation is a critical property of a transactional system that manages single or multiple transactions simultaneously. To prevent interference with each other, an isolated environment is created for each transaction. A good example of this is when two transactions for a $150 withdrawal begin at the same time, with each operation being carried out independently. This ensures that when both operations are completed, the balance will be $0 rather than $150.

### Durability

Durability ensures that changes are maintained after a transaction completes and is written to the database. By doing this, it is guaranteed that data in the system will be saved even in the event of system breakdowns, power outages, etc.

## Why are ACID Principles important?

ACID principles are important because they ensure that the data remains consistent and trustworthy, even when unexpected errors occur. They provide a reliable way to manage database transactions and ensure that the data is always available and accessible to users. Without the ACID principles, the integrity and consistency of the data would be compromised, leading to a loss of trust in the system and potentially significant consequences for the organization. Therefore, it is essential to understand and implement the ACID principles in any database management or software development project.

## Conclusion

ACID principles are crucial for ensuring the integrity and consistency of data in any database management or software development project. By providing a reliable way to manage transactions, ACID principles ensure that data remains available and accessible to users, even in the event of unexpected errors or system failures. As such, organizations need to understand and implement ACID principles to maintain trustworthy and consistent data and avoid the potential consequences of compromised data integrity.

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