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Aborting Transacions

COMP207 Lectures

Reasons For Transaction Abortions

Errors while executing transactions:

  • Violation of integrity constraints, other run-time errors.
    • Multiple people in a seat that should only relates to one customer.

Deadlocks:

  • Concurrency control requests to abort transactions.
    • When using two-phase locking.

Explicit Request:

  • User says ROLLBACK; after they START TRANSACTION;.

Reasons Beyond the DBMS’s Control

Media Failure:

  • The medium holding the database becomes partially or completely unreadable.

Can be guarded against by using archives and controlled redundancy with RAID.

Catastrophic Events:

  • The medium holding the database is destroyed.

Can be guarded against by having archives at safe, different locations.

System Failures:

  • Information about the active transaction’s state is lost.
    • Could be due to power failures or software errors.