ACID stands for Atomicity, Consistency, Isolation, and Durability—four key properties that ensure reliable processing of database transactions. These properties help maintain data integrity and prevent data corruption in case of failures.

1. Atomicity (All or Nothing)

• Ensures that a transaction is either fully completed or fully rolled back.
• If one part of a transaction fails, the entire transaction is undone (rolled back).
• Example:
  • Transferring money from Account A to Account B should either debit A and credit B completely or not happen at all.

Implementation in ADO.NET:

transaction.Rollback(); // Undo changes if an error occurs

2. Consistency (Valid State)

• Ensures that the database moves from one valid state to another.
• Prevents invalid or corrupted data from being stored.
• Example:
  • If a banking transaction deducts money from an account, the corresponding account should reflect the deducted amount correctly.

Implementation in ADO.NET:

• Use constraints (Primary Key, Foreign Key, Unique, Not Null, etc.) and triggers to enforce consistency.

3. Isolation (Concurrent Transactions Don't Interfere)

• Ensures that concurrent transactions don't interfere with each other.
• Prevents dirty reads, non-repeatable reads, and phantom reads.
• Example:
  • Two users withdrawing money from the same account simultaneously should not cause incorrect balance calculations.

Implementation in ADO.NET:

• Use different isolation levels such as:

transaction = conn.BeginTransaction(IsolationLevel.Serializable);

Isolation Levels in SQL Server:

4. Durability (Permanent Changes)

• Ensures that committed transactions are permanently stored in the database, even in case of system crashes.
• Example:
  • After a successful online purchase, the order remains stored even if the server crashes.

Implementation in ADO.NET:

transaction.Commit(); // Save changes permanently

• Databases ensure durability using logs, checkpoints, and backups.

Summary Table

These properties are crucial for databases like SQL Server, PostgreSQL, MySQL, and Oracle to ensure reliability and data integrity.