Database Transaction Management: Validation, Serializability, and Recovery Strategies
Database Transaction Management
Validation Phase
The validation phase ensures that transactions maintain database consistency and serializability. Checks are performed to prevent serialization violations and ensure data integrity.
Read-Only Validation
For read-only transactions, validation verifies that the read values are current, preventing interference. If inconsistencies are detected, the transaction is rolled back and restarted.
Update Validation
For update transactions, validation determines if the database remains in a consistent state after applying updates. If not, the transaction is rolled back and restarted.
Transaction Scheduling
Transactions are assigned unique integer numbers (t(i)) to ensure serializability. The following conditions must hold for proper scheduling:
- Ti completes its write phase before Tj starts its read phase.
- Ti’s write set doesn’t intersect with Tj’s read set, and Ti completes its write phase before Tj starts its write phase.
- Ti’s write set doesn’t intersect with Tj’s read or write set, and Ti completes its read phase before Tj completes its read phase.
Back and Restore Strategy
Developing a backup and restore strategy involves considering factors such as database access hours, update frequency, and data distribution. Here are some recommendations:
- Schedule full backups during off-peak periods.
- Consider differential backups between full backups for frequent changes.
- Schedule frequent log backups under the full recovery model.
- Utilize partial or file backups for large databases with concentrated changes.
Example: Relational Algebra and SQL Query
Scenario: Retrieve project details for projects located in ‘Stafford’.
Relational Algebra:
πPNUMBER, DNUM, LNAME, ADDRESS, BDATE (((σPLOCATION='STAFFORD'(PROJECT)) ⋈ mgrssn=SSN (employee)) ⋈ dnumber=DNUMBER (department))
SQL Query:
SELECT P.NUMBER, P.DNUM, E.LNAME, E.ADDRESS, E.BDATE FROM PROJECT AS P, DEPARTMENT AS D, EMPLOYEE AS E WHERE P.DNUM=D.DNUMBER AND D.MGRSSN=E.SSN AND P.PLOCATION='STAFFORD';
PL/SQL: Control Flow, Procedures, and Triggers
This section covers PL/SQL concepts like control flow statements (IF…ELSE, CASE), procedures, triggers, and error handling.
Control Flow Statements
Examples demonstrate the use of IF…ELSE statements for conditional execution and CASE expressions for value replacement based on comparisons.
Procedures
Examples illustrate creating and executing stored procedures with and without parameters, as well as dropping procedures.
Triggers
An example showcases creating a trigger on the EMP table to insert records into EMP2 based on income conditions.
Error Handling
Examples demonstrate using TRY…CATCH blocks for exception handling within transactions.
MySQL Events and Backup/Restore
This section covers creating and scheduling MySQL events and performing backup and restore operations in SQL Server.
MySQL Events
Examples demonstrate creating one-time and recurring events to insert messages into a table.
Backup and Restore
Examples illustrate backing up a database to a disk device and restoring a full database backup followed by a differential backup.