Overview
This lecture discusses practical examples of when to use database transactions, explains their core properties (ACID), and helps distinguish scenarios requiring transactions from those that do not.
Database Transactions & ACID Properties
- Database transactions ensure multiple related operations succeed or fail as a unit.
- ACID stands for Atomicity, Consistency, Isolation, and Durability, the four key properties of database transactions.
- Atomicity means either all transaction operations succeed or none do.
- Consistency ensures all database rules and constraints remain valid after a transaction.
- Isolation prevents concurrent transactions from affecting each other's outcomes.
- Durability guarantees that once a transaction is committed, changes are permanent.
When Not to Use Transactions
- Transactions are unnecessary for simple read operations such as SELECT queries, even if executed by many users.
- Single, harmless inserts (e.g., user sign-up) don’t typically require transactions, as a failed operation can simply be retried.
- Updates or deletes also may not require transactions if they do not impact other users or important data integrity.
- However, even single operations may need transactions if they involve isolation issues—e.g., concurrent admin and user updates on the same record.
When to Use Transactions
- Use transactions when multiple queries (insert, update, delete) must all succeed together to maintain data integrity.
- Example: Purchasing a course requires updating user points, enrolling in the course, and recording the transaction in a ledger—these should occur within one transaction.
- If any step fails, all related operations must be rolled back to avoid inconsistent or incorrect data.
- Frameworks allow you to begin a transaction, execute queries, then commit if successful or roll back on failure.
Practical Flow of a Transaction
- Begin the transaction.
- Perform all necessary SQL queries.
- If all succeed, commit the transaction; if any fail, roll back all changes.
Key Terms & Definitions
- Database Transaction — A sequence of operations treated as a single logical unit of work.
- Atomicity — Ensures all operations within a transaction complete successfully or none do.
- Consistency — Maintains database rules and constraints after a transaction.
- Isolation — Keeps transactions separate to avoid interference.
- Durability — Makes committed transaction changes permanent.
Action Items / Next Steps
- Review implementation of transactions in your chosen programming language.
- Analyze your application scenarios to decide where transactions are necessary.
- Practice writing transaction flows with commit and rollback logic.