COMMIT makes a transaction's changes permanent under the database's rules; ROLLBACK cancels uncommitted changes. ACID is not another command. It names properties a transaction system aims to provide. When several transactions run at once, also ask which changes each can see and what survives a failure.
Key terms
A transaction can finish with COMMIT or have its uncommitted work undone with ROLLBACK. ACID describes guarantees around that boundary.
| Term | Meaning |
|---|---|
COMMIT | Completes a transaction and makes its changes durable according to the database's transaction guarantees. |
ROLLBACK | Undoes uncommitted changes made by a transaction, or reverts to a savepoint where supported. It does not undo an already committed transaction. |
SAVEPOINT and CHECKPOINT | A savepoint marks a position for partial rollback within a transaction. A database checkpoint is a separate recovery mechanism involving logs and data pages; it is not a savepoint. |
Procedure | A stored procedure is a callable program of database operations. Calling one does not necessarily define a transaction boundary by itself. |
Trigger | Database logic that runs in response to a specified event, such as an insert, update, or delete. |
Terms to distinguish
| Term | Meaning |
|---|---|
Event | Something that happens in a system. For a database trigger, it is the specified operation or condition that causes the trigger to run. |
Atomicity | A transaction's changes take effect as a unit: either the operation commits as specified or its uncommitted effects are undone. |
Consistency | A committed transaction preserves the database's declared integrity rules and constraints. Application correctness still depends on the rules the application defines. |
Isolation | Concurrent transactions interact according to the selected isolation level. It does not always mean each transaction waits for all others to finish. |
Durability | Once committed, changes survive failures to the extent promised by the database's durability configuration. |
Terms in code
| Term | Meaning |
|---|---|
CRUD | Create, Read, Update, and Delete: four common data operations. |
UNDO | Recovery information or work used to reverse changes. |
REDO | Recovery information or work used to reapply recorded changes. |
Concurrency control | Mechanisms that coordinate simultaneous transactions so they obey the chosen isolation and consistency rules. |
Reading a technical document
COMMITfinishes a successful transaction andROLLBACKundoes uncommitted work. ACID names the properties expected at that boundary.
If the terms blur together, separate the command, the property, and the recovery mechanism. A SAVEPOINT is inside a transaction; a CHECKPOINT serves database recovery and is a different concept.
Key takeaways
Read the transaction boundary, success or cancellation, and concurrent guarantees together.
- COMMIT — Completes the transaction and makes its changes durable under the database's rules.
- Consistency — Preserves declared integrity rules when a transaction commits.
- Concurrency control — Coordinates transactions so concurrent work follows the chosen rules.
