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BCA Cyber Security Database Management Systems — practice questions — page 2

Explore 56 free Database Management Systems questions in BCA Cyber Security Computer Science. Open each question or exercise to read its content, reference answers and available explanation.

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Database Management Systems questions and exercises with answers

Showing questions 31–56 of 56.

If T1 writes A, T2 reads that new A before T1 commits, and T1 then aborts, T2 has experiencedRead the answer and worked solution →From strictest to weakest, the correct hierarchy of schedules isRead the answer and worked solution →The DBMS detects a deadlock by findingRead the answer and worked solution →Thomas's Write Rule, applied to the case TS(T) < W-timestamp(Q), says toRead the answer and worked solution →Which is NOT a recovery-relevant failure type per the chapter?Read the answer and worked solution →Stable storage is implemented byRead the answer and worked solution →The write-ahead rule states thatRead the answer and worked solution →A complete log record for a write operation includesRead the answer and worked solution →After a crash, with checkpointing, the recovery system scans the logRead the answer and worked solution →Fuzzy checkpoints differ from naive checkpoints byRead the answer and worked solution →ARIES recovery is structured as exactlyRead the answer and worked solution →What is the purpose of a Compensation Log Record (CLR) in ARIES?Read the answer and worked solution →Degree or cardinalityRead the answer and worked solution →Primary or foreign keyRead the answer and worked solution →Type the database termRead the answer and worked solution →Say it the relational wayRead the answer and worked solution →Count the relationRead the answer and worked solution →Pop what a DBMS doesRead the answer and worked solution →One word is wrongRead the answer and worked solution →Order the case for a DBMSRead the answer and worked solution →Candidate or primary keyRead the answer and worked solution →Which one does not belongRead the answer and worked solution →Rows or columnsRead the answer and worked solution →Spot the false statementRead the answer and worked solution →Which ones belongRead the answer and worked solution →Database concepts bingoRead the answer and worked solution →

Worked practice questions

If T1 writes A, T2 reads that new A before T1 commits, and T1 then aborts, T2 has experienced

  1. a phantom read anomaly
  2. a dirty read of uncommitted data
  3. an unrepeatable read anomaly
  4. a lost update problem
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Correct answer: B. a dirty read of uncommitted data

Reading data written by an uncommitted transaction (which then rolls back) is the textbook dirty read. The value T2 saw was never officially in the database. Phantom involves new rows appearing unrepeatable read involves the same row changing across two reads in the same transaction lost update involves concurrent writes overwriting each other.

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From strictest to weakest, the correct hierarchy of schedules is

  1. recoverable > strict > cascadeless
  2. cascadeless > recoverable > strict
  3. strict > cascadeless > recoverable
  4. they are independent properties, no hierarchy exists
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Correct answer: C. strict > cascadeless > recoverable

Every strict schedule is cascadeless (no read of uncommitted data follows from no read OR write of uncommitted data). Every cascadeless schedule is recoverable. So strict implies cascadeless implies recoverable. The reverse implications do not hold recoverable is the weakest of the three, strict the strongest.

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The DBMS detects a deadlock by finding

  1. two transactions with the same start timestamp
  2. a chain of more than 3 waiting transactions
  3. a transaction that has aborted more than once
  4. a directed cycle in the wait-for graph
Show answer and solution

Correct answer: D. a directed cycle in the wait-for graph

A cycle in the wait-for graph means each transaction in the cycle is waiting for a lock held by the next one, and no one can move. Detection = periodically run a cycle-finding algorithm on the graph. Same timestamp, chain length and abort history are unrelated to deadlock detection.

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