After analysis on the slow query log on a high-end OLTP service, the table identified in the slow queries is: CREATE TABLE transactions ( User VARCHAR (255) NOT NULL, Amount DECIMAL (16,2) NOT NULL…

Question

Options

• AThe Date should be a TIMESTAMP field for better performance.
• BThe User field is too long for most names.
• CThe engine type is not appropriate to the application use.
• DUsing default values for DATETIME causes table scans.
• ENo indexes are defined.

• A
  11% (2)
• B
  63% (12)
• D
  5% (1)
• E
  21% (4)

Explanation

C is the strongest correct answer: MyISAM uses table-level locking rather than row-level locking, making it a poor fit for a high-concurrency OLTP workload - every write locks the entire table, serializing concurrent transactions and directly explaining slowness under load. B is correct because VARCHAR(255) is unnecessarily oversized for a user/name field; MySQL must account for the maximum declared length when building in-memory temporary tables during sorting and grouping operations, consuming excess memory and degrading query performance.

Why the distractors are wrong: A is incorrect - DATETIME and TIMESTAMP have minor storage differences (8 vs 4 bytes) but neither causes meaningful OLTP slowness. D is a fabrication - default values on DATETIME have no relationship to table scans. E is the trickiest distractor: while absent indexes would absolutely cause slowness, the question asks for the most likely causes given this specific output, meaning the structural design flaws (wrong engine, oversized column) are the root problems the schema itself reveals.

Note: In real-world analysis, C and E would both be flagged immediately; the question may have a debatable answer, but for exam purposes, focus on the MyISAM/OLTP mismatch as the definitive answer.

Memory tip: Think "OLTP = InnoDB" - MyISAM is for read-heavy, non-concurrent workloads (like analytics), while InnoDB's row-level locking is what keeps high-transaction systems fast. If you see MyISAM + OLTP together, that's always a red flag.

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