Choose the description that is incorrect regarding the differences between in-memory...
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Choose the description that is incorrect regarding the differences between in-memory databases and traditional databases like MySQL or PostgreSQL.
Show answer & explanation
Option B is fundamentally incorrect. In-memory databases store data in RAM, which is volatile—data is lost when power is cut or the system crashes. They are actually less resilient to physical failure compared to disk-based databases like MySQL/PostgreSQL, which persist data to stable storage. Options A, C, and D are all correct: in-memory DBs are faster (A), they rely on sufficient RAM capacity and often use eviction policies like LRU (C), and Redis/Memcached are standard examples (D).
Step-by-step Derivation:
Evaluate each statement:
- A: TRUE—RAM access (nanoseconds) is orders of magnitude faster than disk I/O (milliseconds).
- B: FALSE—RAM is volatile. Power loss or crashes cause immediate data loss. Disk-based DBs survive hardware failures better because data persists to non-volatile storage.
- C: TRUE—In-memory DBs need enough RAM to hold all active data. When capacity is exceeded, they employ eviction policies (LRU, LFU, TTL) to free memory, not just delete infrequently used rows.
- D: TRUE—Redis and Memcached are canonical in-memory database/cache examples.
The question asks for the incorrect statement, so the answer is B.