Technology Certifications Database Management & Security 2

Question 1

Which transaction isolation level prevents dirty reads but still allows non-repeatable reads?

Accepted Answer

Read Committed

Answer

Read Committed only lets a transaction see committed data, but a row can change between two reads.

Question 2

Under the ANSI SQL standard, which isolation level is the only one guaranteed to prevent phantom reads?

Accepted Answer

Serializable

Answer

Serializable makes transactions behave as if run one after another, which eliminates phantoms.

Question 3

A table is in 2NF but a non-key column depends on another non-key column. Which normal form does it violate?

Accepted Answer

3NF

Answer

3NF removes transitive dependencies between non-key attributes.

Question 4

What is the main purpose of write-ahead logging (WAL) in a DBMS?

Accepted Answer

Ensure changes are logged before data pages are written so the database can recover

Answer

Logging changes first lets the DBMS redo or undo work after a crash, which supports atomicity and durability.

Question 5

Transaction A holds a lock on row 1 and waits for row 2, while Transaction B holds row 2 and waits for row 1. What is this?

Accepted Answer

Deadlock

Answer

A deadlock is a circular wait in which each transaction holds a lock the other one needs.

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