Monday, 4 April 2016

Types of failures that causes a transaction to fail

Types of failures that causes a transaction to fail, Reasons for transaction failures, List the reasons for transaction failure in dbms, transaction failure

Types of failures that causes a transaction to fail

A transaction may fail due to one or more following reasons;

  • Computer failure (System crash) – A hardware, software, or network error may cause a computer to fail or hang during an ongoing transaction.
  • Transaction error – This error happens when user aborts the transaction, or logical programming error, or some operations like division by zero, etc.
  • External causes, exception conditions – A transaction may be failed if necessary data not found, or an exception condition met. For example, customer A tries to purchase an item online. Assume that only two such items are available when A starts his transaction and both of them purchased by other customers. When A reaches end of the transaction, the items are not available hence the transaction is cancelled or failed.
  • Concurrency control enforcement – If a transaction causes deadlock or violates serializability, then concurrency control schemes will force the transaction to abort.
  • Disk failure - Some disk blocks may lose their data because of a read or write malfunction or because of a disk read/write head crash. This may happen during a read or a write operation of the transaction.

The failures that are caused because of computer failure, transaction error, external causes, or concurrency control enforcement can be recovered if sufficient data is maintained (for example, transaction logs in log based recovery). These failures are some of the reasons that states the need of recovery subsystem in DBMS.
The failure that is caused by disk failure can be handled differently. For example, if we maintain a backup disk, the data can be restored.


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