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COMMIT and ROLLBACK at a glance
| Aspect | COMMIT |
ROLLBACK |
|---|---|---|
| Purpose | Accept and finalize the current transaction | Cancel uncommitted work in the current transaction |
| Data effect | Changes become durable under normal transactional semantics and become available to other sessions according to the database’s isolation rules | Changes made since the transaction began are discarded |
| Transaction state | Normally ends the current transaction | Normally ends the current transaction |
| Can it reverse an earlier commit? | No | No |
| Savepoints | Removes the transaction’s savepoints | Removes savepoints when the whole transaction is rolled back; ROLLBACK TO SAVEPOINT is used for partial recovery |
| Typical use | All required work succeeded and should be kept | An operation failed, validation rejected the result, or the user canceled |
Oracle documents the permanence, savepoint, and lock effects of transaction control, while MySQL documents visibility and InnoDB lock release after COMMIT or ROLLBACK (Oracle; MySQL InnoDB).
What a SQL transaction is
A transaction is a logical unit of one or more SQL statements. The database treats the unit as a whole: the application either commits the required changes or rolls them back before they are finalized.
Example: an account transfer
BEGIN;
UPDATE accounts
SET balance = balance - 100
WHERE account_id = 1;
UPDATE accounts
SET balance = balance + 100
WHERE account_id = 2;
COMMIT;If the credit update fails, issue ROLLBACK instead of COMMIT. The debit then is not retained, provided both statements are in the same active, transactional context. PostgreSQL describes this all-or-nothing pattern and transaction visibility in its transaction tutorial.
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How COMMIT works
It ends the current unit of work
COMMIT tells the database that every required statement in the current transaction succeeded. Under normal transactional semantics, those changes survive a later connection close or process restart.
It changes visibility and resources
Other sessions can observe committed changes according to the database’s isolation behavior. Common engines also release transaction-held locks and other resources at commit; exact details are engine-specific. The transaction’s savepoints are removed.
It is not reversible with ROLLBACK
After a successful commit, ordinary rollback cannot undo the work. Reversal requires a new compensating transaction, a history or temporal mechanism, or recovery from a backup.
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How ROLLBACK works
Full rollback
BEGIN;
DELETE FROM orders
WHERE order_id = 1001;
ROLLBACK;The delete is canceled if it has not already been committed and the operation is supported by the database and storage engine. A full ROLLBACK ends the current transaction in ordinary modes and commonly releases its locks.
Rollback is limited to the current uncommitted transaction
ROLLBACK cannot undo an autocommitted statement, an earlier explicit commit, work in another session, or changes made by a separate system. It is not a general-purpose undo button.
Autocommit: why rollback may appear not to work
In autocommit mode, each successful statement is committed automatically as its own transaction. If you run an UPDATE and then type ROLLBACK, the update may remain because its transaction already ended.
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Use an explicit transaction before changing data
START TRANSACTION;
UPDATE inventory
SET quantity = quantity - 1
WHERE product_id = 10;
-- Inspect the result, then choose one:
COMMIT;
-- or ROLLBACK;BEGIN, START TRANSACTION, and BEGIN TRANSACTION are common forms, but the accepted syntax depends on the database. MySQL supports START TRANSACTION and BEGIN; its default autocommit behavior is documented in the transaction-control reference. PostgreSQL runs each successful statement in an implicit transaction when no explicit transaction block is open (PostgreSQL tutorial).
Partial rollback with SAVEPOINT
A savepoint lets you discard only the work performed after a named point while keeping earlier work in the transaction.
BEGIN;
UPDATE accounts
SET balance = balance - 100
WHERE account_id = 1;
SAVEPOINT after_debit;
UPDATE accounts
SET balance = balance + 100
WHERE account_id = 999; -- wrong account
ROLLBACK TO SAVEPOINT after_debit;
UPDATE accounts
SET balance = balance + 100
WHERE account_id = 2;
COMMIT;The debit remains, the incorrect credit is removed, and the corrected credit is committed. PostgreSQL’s ROLLBACK TO SAVEPOINT documentation explains that work after the savepoint is discarded while earlier work remains. A full ROLLBACK would discard both operations.
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What happens when a statement fails?
There is no single cross-database rule. Depending on the engine, error, and client library:
- Only the failed statement may be rolled back while the transaction remains active.
- The transaction may enter an error state and require a full rollback before more commands can run.
- The driver or framework may automatically roll back.
- The application may catch the error and accidentally commit other statements.
MySQL documents statement-level behavior for errors such as duplicate-key violations. PostgreSQL commonly requires ROLLBACK or ROLLBACK TO SAVEPOINT after a transaction has entered an error state. Check the product and driver documentation rather than assuming that an error always rolls back everything.
Database-specific differences
| Database | Important qualification |
|---|---|
| PostgreSQL | Without an explicit block, each successful statement has an implicit transaction; savepoints support partial rollback. See the transaction tutorial. |
| MySQL | Autocommit is enabled by default. Storage engine and implicit-commit rules matter, especially when using InnoDB. See transaction control and InnoDB behavior. |
| SQL Server | Autocommit is the normal mode. Nested transaction syntax does not provide independent nested commits; use savepoints for partial recovery. See Microsoft’s transaction guide. |
| Oracle Database | Transactions and savepoints are explicit concepts; COMMIT removes savepoints and releases locks. Oracle’s transaction-control documentation also recommends explicitly ending transactions in application code. |
| SQLite | Transactions can begin implicitly when a database-accessing command runs. Savepoints form a stack; releasing the outermost savepoint commits. See SQLite’s transaction and savepoint documentation. |
DDL and nontransactional operations
Do not assume that every SQL statement can be rolled back. INSERT, UPDATE, and DELETE are commonly transactional, but CREATE, ALTER, DROP, and administrative commands may cause an implicit commit, be prohibited inside an explicit transaction, or have product-specific rollback behavior. MySQL lists implicit-commit statements in its transaction-control documentation; SQL Server documents commands with special transaction restrictions in its transaction guide.
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MySQL rollback guarantees also depend on the table’s storage engine. InnoDB is transaction-oriented; nontransactional storage does not provide identical guarantees (MySQL InnoDB documentation).
Connection closing and application code
Closing a connection often rolls back uncommitted work, but this is implementation-specific. MySQL rolls back the final uncommitted transaction when a session ends with autocommit disabled, and Oracle describes rollback after abnormal termination. Both recommend explicitly committing or rolling back instead of relying on connection failure.
Client libraries may expose methods rather than SQL commands. The transaction owner should normally end the transaction on every success and failure path:
Quick Recap
begin transaction
try:
perform all related operations
commit
except error:
rollback
rethrow errorPractical rules that prevent data loss
- Start the transaction before the first related data change.
- Keep all statements that must succeed together in the same transaction.
- Validate results before committing.
- Commit only after the final required step succeeds.
- Roll back on failure, cancellation, or inconsistent intermediate results.
- Use savepoints when only an optional portion should be retried or discarded.
- Keep transactions focused; long transactions hold locks, consume log or undo resources, increase contention, and can make rollback more expensive.
- Verify autocommit, DDL rules, storage-engine support, and driver error behavior for the specific database.
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