Choose the statement that is INCORRECT regarding in-memory databases (e.g., Redis,...
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Choose the statement that is INCORRECT regarding in-memory databases (e.g., Redis, Memcached) compared to traditional disk-based RDBMS (e.g., PostgreSQL):
Show answer & explanation
Option B is factually incorrect. Traditional disk-based RDBMS systems (PostgreSQL, MySQL, Oracle) are specifically designed to support full ACID transactions and guarantees. In-memory databases supplement these capabilities with speed, not replace them. Options A, C, and D are all correct: in-memory databases do leverage RAM for speed, they use snapshots/AOF for durability, and RAM is indeed more expensive per gigabyte than disk storage.
Step-by-step Derivation:
The question asks for the INCORRECT statement. Evaluate each:
Option A (TRUE): RAM access is nanoseconds vs. disk I/O which is milliseconds. In-memory databases exploit this fundamental hardware advantage for low latency.
Option B (FALSE/INCORRECT): Traditional disk-based RDBMS like PostgreSQL and MySQL provide full ACID compliance through write-ahead logging (WAL), locking mechanisms, and crash recovery. This is a core feature, not a limitation.
Option C (TRUE): Redis uses RDB snapshots (point-in-time) and AOF (append-only file) for persistence. Memcached typically lacks durability by design.
Option D (TRUE): 1 GB of DRAM costs approximately $2-5, while 1 GB of SSD storage costs $0.05-0.20. This cost differential drives architectural choices.
The answer is B because it makes a false claim about traditional RDBMS capabilities.