What are the possible reasons why a database transaction is not rolled back?

Possible reasons why a database transaction is not rolled back include:

1. Explicit Commit Instead of Rollback: If the application or code explicitly issues a COMMIT statement instead of a ROLLBACK, the transaction will be finalized, and changes will persist.

   • Example: A developer mistakenly writes COMMIT; after an error occurs instead of ROLLBACK;.

2. Transaction Already Committed: If the transaction was successfully committed before the error was detected, rolling back becomes impossible.

   • Example: A long-running transaction completes successfully, but a subsequent unrelated error leads to an incorrect assumption that a rollback is needed.

3. Database Connection Lost Before Rollback: If the database connection is terminated before a ROLLBACK is executed, the database may automatically commit the transaction (depending on the isolation level and configuration).

   • Example: A network failure disconnects the application from the database before the rollback logic is reached.

4. No Error Handling in Code: If the application lacks proper error-handling mechanisms, exceptions may bypass the rollback logic.

   • Example: A try-catch block omits the ROLLBACK statement, allowing the transaction to remain active.

5. Database-Specific Behavior: Some databases may automatically commit transactions under certain conditions, such as when a DDL (Data Definition Language) statement is executed.

   • Example: In some databases, running CREATE TABLE within a transaction forces an implicit commit.

6. Deadlocks or Timeouts: If a transaction is terminated due to a deadlock or timeout, the database may automatically resolve it by committing or rolling back, depending on the configuration.

   • Example: A transaction is killed by the database due to a deadlock, and the system defaults to committing the changes.

To ensure reliable transaction management, use cloud databases like TencentDB for MySQL or TencentDB for PostgreSQL, which provide automated backup, failover, and transaction monitoring to minimize such issues.