Database Management & Security Flashcards
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Read the first 7 Database Management & Security flashcards as text
Which transaction isolation level prevents dirty reads but still allows non-repeatable reads?
Answer: Read Committed
Read Committed only lets a transaction see committed data, but a row can change between two reads.
Under the ANSI SQL standard, which isolation level is the only one guaranteed to prevent phantom reads?
Answer: Serializable
Serializable makes transactions behave as if run one after another, which eliminates phantoms.
A table is in 2NF but a non-key column depends on another non-key column. Which normal form does it violate?
Answer: 3NF
3NF removes transitive dependencies between non-key attributes.
What is the main purpose of write-ahead logging (WAL) in a DBMS?
Answer: Ensure changes are logged before data pages are written so the database can recover
Logging changes first lets the DBMS redo or undo work after a crash, which supports atomicity and durability.
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?
Answer: Deadlock
A deadlock is a circular wait in which each transaction holds a lock the other one needs.
What does the two-phase commit (2PC) protocol guarantee?
Answer: All participating nodes in a distributed transaction either commit or roll back together
2PC uses a prepare phase and a commit phase so a distributed transaction stays atomic.
What is the most common reason to denormalize a database schema?
Answer: To improve read and query performance
Denormalization adds controlled redundancy to cut down on joins and speed up reads.
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