FAILURE CLASSIFICATION
Failure classification in a Database Management System (DBMS) is essential for understanding the different types of failures that can occur and designing appropriate recovery mechanisms.
1. Transaction Failures
Transaction failures occur when a transaction cannot complete successfully. This can happen for various reasons:
- Logical Errors: These are errors within the transaction's logic, such as division by zero, trying to insert a duplicate key in a unique column, etc.
- System Errors: These occur when the database system detects a problem with the transaction, such as deadlock detection and aborting one of the transactions to resolve the deadlock.
2. System Failures
System failures, also known as soft failures, happen when the database system crashes or shuts down unexpectedly due to reasons such as:
- Hardware Failures: These include issues like CPU failures, power outages, or memory failures.
- Software Failures: These involve bugs in the DBMS software, operating system crashes, or unexpected reboots.
System failures affect the DBMS but do not damage the database stored on disk. The database can typically be recovered from a system failure using transaction logs and checkpoints.
3. Media Failures
Media failures, also known as hard failures, occur when the storage media holding the database becomes damaged or corrupted. Examples include:
- Disk Crashes: Physical damage to the disk that stores the database.
- File System Corruption: Issues with the file system that lead to the loss or corruption of database files.
Media failures can result in the loss of data unless proper backup and recovery mechanisms are in place.
4. Application Failures
Application failures occur due to errors in the application programs that interact with the database. These errors can be due to:
- Application Logic Errors: Bugs or flaws in the application code that lead to incorrect database operations.
- Misuse of Database APIs: Incorrect usage of the database's application programming interfaces (APIs), leading to unintended results or failures.
5. Concurrency Control Failures
Concurrency control failures happen when multiple transactions interfere with each other, leading to problems such as:
- Deadlocks: Two or more transactions waiting indefinitely for resources held by each other.
- Lost Updates: When two transactions simultaneously update the same data, leading to one update being lost.
- Inconsistent Retrievals: When a transaction reads data that is being modified by another transaction, leading to inconsistent or incorrect data retrieval.