Database / SQLite Interview questions

Explain the lifecycle of a SQLite transaction from BEGIN to COMMIT?

Calling BEGIN starts an explicit transaction, and every statement afterward operates within it until either COMMIT makes the changes permanent or ROLLBACK discards them.

flowchart TD
    A[BEGIN] --> B[Statements execute, journal/WAL records original or new page state]
    B --> C{COMMIT or ROLLBACK?}
    C -->|COMMIT| D[Changes finalized; journal deleted or WAL checkpointed]
    C -->|ROLLBACK| E[Journal used to restore original data; changes discarded]

Under the hood, in rollback journal mode, SQLite copies each page's original content into the journal file before modifying it in the main database, so a ROLLBACK simply restores those original pages. On COMMIT, the journal file is deleted (its job done) and the modified pages remain in place. In WAL mode, the mechanics differ (new pages go to the WAL rather than the journal), but the guarantee is the same: until COMMIT actually completes, an interrupted transaction (a crash, a ROLLBACK) leaves the database exactly as it was beforehand.

Take quiz

What does SQLite do with each page's original content before modifying it, in rollback journal mode? Discards it immediately

✗ Not quite. Try again.

Copies it into the journal file first, so ROLLBACK can restore it

✓ Correct! Well done.

Sends it to a remote backup server

✗ Not quite. Try again.

What guarantee holds if a crash occurs before COMMIT completes? The database is left in a corrupted, unpredictable state

✗ Not quite. Try again.

The database is left exactly as it was before the transaction started

✓ Correct! Well done.

Only half of the changes are applied

✗ Not quite. Try again.

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Database / SQLite Interview questions

Explain the lifecycle of a SQLite transaction from BEGIN to COMMIT?

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