SQLite Transactions and Atomicity Fundamentals Quiz Quiz

Explore the core principles of transactions and atomicity in SQLite, including commit and rollback operations, isolation, and the behavior of transaction statements. Ideal for learners seeking clarity on how SQLite handles reliable data changes and ensures database consistency.

1. Transaction Begin Statement

   Which command starts a new transaction in SQLite to ensure subsequent changes are atomic?

   1. START TRANSACT;
   2. OPEN TRANSACTION;
   3. INITIATE TRANSACTION;
   4. BEGIN TRANSACTION;

   Explanation: The correct statement to start a new transaction is BEGIN TRANSACTION;. This command signals SQLite to treat the following operations as a single atomic block. The options START TRANSACT;, OPEN TRANSACTION;, and INITIATE TRANSACTION; are not valid in SQLite and may be confused with terms from other systems or are simply not recognized.

2. Ensuring Atomicity

   What does atomicity in the context of an SQLite transaction guarantee for a set of database operations?

   1. All changes are made completely or none at all.
   2. Operations are distributed across multiple servers.
   3. Transactions are logged to external files.
   4. Each operation is performed at maximum speed.

   Explanation: Atomicity ensures that either all operations within a transaction are fully completed or, if an error occurs, none are applied. The option about speed is unrelated to atomicity, while logging and distribution reference different database concepts. Only the first option captures the essence of atomicity.

3. Purpose of ROLLBACK

   If a critical error occurs before committing a transaction, which SQL command should you use in SQLite to undo all operations since the transaction began?

   1. REVERSE;
   2. CANCEL TRANSACTION;
   3. CONFIRM;
   4. ROLLBACK;

   Explanation: The correct command to undo operations in a transaction is ROLLBACK;. CONFIRM; and CANCEL TRANSACTION; are not valid SQL commands, and REVERSE; does not exist in SQLite. ROLLBACK; ensures all interim changes are discarded if an error happens before committing.

4. Committing a Transaction

   After executing several changes in a transaction, which command will make the changes permanent in SQLite?

   1. CONFIRM TRANSACTION;
   2. SAVE;
   3. APPLY CHANGES;
   4. COMMIT;

   Explanation: COMMIT; finalizes a transaction and makes all changes permanent. SAVE;, APPLY CHANGES;, and CONFIRM TRANSACTION; may sound logical, but they are not valid SQLite commands for this purpose. COMMIT; uniquely applies the intended functionality.

5. Default Transaction Behavior

   What is SQLite’s default behavior if you execute an update without explicitly beginning a transaction?

   1. The change is not saved until a manual commit.
   2. It will refuse to run the update.
   3. It automatically wraps the statement in its own transaction.
   4. The database will become locked until COMMIT is issued.

   Explanation: If no explicit transaction is started, SQLite automatically wraps each statement in its own transaction to ensure atomicity. It does not refuse the update, nor does it lock the database unnecessarily or require a manual commit in this scenario. Only the first option accurately describes the automatic handling.

6. Concurrent Transactions

   In SQLite, what happens if two transactions try to write to the same database at the same time?

   1. One transaction will wait for the other to finish.
   2. Both transactions will merge their changes automatically.
   3. The database allows simultaneous writes by default.
   4. One transaction is immediately rolled back.

   Explanation: When two transactions attempt simultaneous writes, SQLite lets one transaction proceed while the other waits for the lock to be released, ensuring data consistency. Automatic merging and simultaneous writes can cause corruption, so SQLite prevents this. Immediate rollback does not occur unless a serious error is detected.

7. Savepoints in Transactions

   How does a SAVEPOINT in SQLite help during complex transactions with multiple stages?

   1. It ends the transaction and starts a new one.
   2. It locks the table for exclusive access.
   3. It allows partial rollback to a specific point within the transaction.
   4. It immediately commits part of the transaction.

   Explanation: A SAVEPOINT lets you roll back part of a transaction to a designated point, which is useful in multi-step processes. Committing, ending transactions, or locking tables are not the purposes of savepoints. Savepoints provide fine-grained control over transaction changes.

8. Transaction Isolation

   What does transaction isolation in SQLite primarily prevent?

   1. Conflicting reads and writes from other transactions.
   2. Deleting records by mistake.
   3. Creating duplicate table names.
   4. System crashes during an update.

   Explanation: Transaction isolation aims to prevent the adverse effects of one transaction on another, particularly from simultaneous reads or writes. Mistaken deletions, system crashes, and table naming are unrelated to the concept of isolation in transactions.

9. Autocommit Mode

   When is autocommit mode active in SQLite?

   1. During the execution of the COMMIT command.
   2. Only after issuing a BEGIN command.
   3. When there is no active transaction.
   4. While using exclusive locks.

   Explanation: Autocommit mode is enabled when there is no explicit transaction in progress. It is suspended after BEGIN and is unrelated to exclusive locks or the brief moment during COMMIT execution. The first option accurately reflects this setting.

10. Effects of COMMIT on Savepoints

    What happens to created SAVEPOINTs when a transaction is committed in SQLite?

    1. An error is thrown unless each is released.
    2. They persist for future transactions.
    3. All SAVEPOINTs are released automatically.
    4. They must be manually deleted before COMMIT.

    Explanation: Once a transaction is committed, all nested SAVEPOINTs are automatically released by SQLite. There is no need to delete them manually, they do not persist between transactions, and committing does not generate an error if SAVEPOINTs still exist.