🔐 What Are ACID Properties?
ACID is an acronym for the four key properties that guarantee reliable processing of database transactions in a Relational Database Management System (RDBMS). These properties ensure data integrity, consistency, and reliability, even in the face of system failures or concurrent access.
🧩 ACID Breakdown
| Property | Description |
|---|---|
| A — Atomicity | A transaction is all or nothing. If one part fails, the entire transaction fails and no changes are applied. |
| C — Consistency | A transaction must bring the database from one valid state to another, maintaining all defined rules, constraints, and invariants. |
| I — Isolation | Transactions must be executed independently. Intermediate states are invisible to other transactions. |
| D — Durability | Once a transaction is committed, its changes are permanent, even if the system crashes immediately after. |
🔧 Example: Money Transfer Between Accounts
Say you’re transferring ₹1000 from Account A to B.
Transaction steps:
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Debit ₹1000 from Account A
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Credit ₹1000 to Account B
Here’s how ACID applies:
| Property | Impact on Transaction |
|---|---|
| Atomicity | If step 2 fails (e.g., app crash), step 1 is rolled back — money isn’t lost. |
| Consistency | After the transfer, the total money across both accounts remains the same. |
| Isolation | If two transfers happen at the same time, they don’t interfere with each other’s calculations. |
| Durability | Once committed, the transfer is guaranteed to persist, even after a power failure. |
⚠️ Why ACID Matters
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Critical in banking, e-commerce, and booking systems.
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Prevents issues like double-spending, dirty reads, lost updates, etc.
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RDBMS like PostgreSQL, MySQL, Oracle implement strong ACID guarantees.
🆚 ACID vs BASE (NoSQL)
| Feature | ACID (RDBMS) | BASE (NoSQL, often) |
|---|---|---|
| Model | Strict, consistent | Relaxed, eventually consistent |
| Focus | Accuracy, reliability | Scalability, availability |
| Use Case | Financial systems, transactions | Big data, real-time analytics |
Summary:
ACID = Trustworthy Transactions.
If you need strict accuracy, no data loss, and controlled concurrency, ACID is non-negotiable. If you’re building highly scalable but less sensitive systems, you might trade off some ACID for performance.