What is meant by database recovery services?
True or False: An event-oriented log in database auditing and system security usually contains sequential records describing system events, application events, or user events.
A.True
B.False
Explain the concept of Database Recovery Services and state their primary objective.
While recovering database data after a sudden system crash or failure, which of the following files does a recovery manager examine first to identify transaction states?
A.A system file
B.Log file
C.Data dictionary
D.Metadata
Under multi-user database concurrency rules, which of the following statements correctly distinguishes between a Shared Lock (S) and an Exclusive Lock (X) during transaction execution?
💻 sql Snippet
-- Transaction A requests a Shared Lock (S):
SELECT * FROM Patients WITH (HOLDLOCK) WHERE PatientID = 105;
A.Multiple transactions can hold a Shared Lock on the same data resource simultaneously for reading, but an Exclusive Lock blocks all other locks to allow writing.
B.An Exclusive Lock allows multiple transactions to write data simultaneously, whereas a Shared Lock blocks all transactions.
C.Shared Locks are used exclusively for deleting rows, while Exclusive Locks are applied only during CREATE TABLE operations.
D.A Shared Lock is a DDL command that prevents table alterations, whereas an Exclusive Lock is a DML command used for updates.
Under multi-user database transaction management, the Two-Phase Locking (2PL) protocol is used to guarantee serializability. Which of the following is correct regarding the Growing and Shrinking phases of the 2PL protocol?
💻 text Snippet
-- Transaction structure under Two-Phase Locking (2PL):
-- Phase 1 (Growing): Acquire Lock S(A), Acquire Lock X(B)
-- Operation: Read(A), Write(B)
-- Phase 2 (Shrinking): Release Lock S(A), Release Lock X(B)
A.During the Growing Phase, a transaction can acquire locks but cannot release any. During the Shrinking Phase, a transaction can release locks but cannot acquire new ones.
B.During the Growing Phase, a transaction can only release locks. During the Shrinking Phase, it can only acquire locks.
C.A transaction is allowed to acquire and release locks freely in both phases as long as the total number of locks remains constant.
D.Locks can only be acquired during the growing phase, and locks can only be released after the entire transaction commits.
Under multi-user transaction concurrency control rules, which of the following is correct regarding the operational compatibility of Shared (S) and Exclusive (X) lock modes?
💻 sql Snippet
-- Transaction A: Read-only (S Lock)
SELECT * FROM Accounts WITH (HOLDLOCK) WHERE AccID = 101;
A.A Shared lock (S) is compatible with another Shared lock (S) on the same data item, but an Exclusive lock (X) is incompatible with any other Shared (S) or Exclusive (X) lock.
B.An Exclusive lock (X) is compatible with other Shared locks (S) to allow concurrent dirty reads but prevents concurrent writes.
C.A Shared lock (S) is incompatible with another Shared lock (S) on the same data item to prevent inconsistent analysis errors.
D.Both lock modes are fully compatible with each other on the same data item, as conflict resolution is managed entirely by check-pointing.
While recovering database data after a sudden system crash or power failure, which of the following files does the DBMS recovery manager examine first to identify transaction states?
A.A system file
B.Log file
C.Data dictionary
D.Metadata
In database systems, what is meant by database recovery services and what is their primary objective during system or hardware failures?
💻 text Snippet
-- Recovery Manager sequence:
-- 1. Identify most recent checkpoint.
-- 2. Scan log forward:
-- - REDO committed transactions (forward list).
-- - UNDO active/aborted transactions (backward list).
What is meant by database recovery services, and how does the Recovery Manager perform database crash recovery under the Incremental Log with Deferred Updates approach?
💻 text Snippet
-- Conceptual layout of Deferred Updates Logging:
-- [Transaction Writes] ---> [Log Buffer in RAM] ---> (Commit) ---> [Physical Log Disk] ---> [Database Files on Disk]
