[calmcoconut]

Summary

Audit and improvement of Chapter 7 (Sharding) multiple choice question distractors. Several wrong answer options were too obviously absurd or off-topic, making the correct answer easy to identify without domain knowledge. This PR replaces them with plausible alternatives that require genuine understanding to eliminate.

Questions Changed

Question	Issue	Fix
Q2 — Single-machine per-core sharding DBs	Options C/D named completely unrelated DB categories (cluster DBs, cloud warehouses)	Replaced with high-performance analytical DBs (Elasticsearch/ClickHouse/ScyllaDB, TimescaleDB/InfluxDB/QuestDB) that a learner might plausibly confuse
Q9 — Why language hash functions are unsuitable	Option C claimed hash functions "only work on integers" — obviously false to anyone who has used hashCode() on a String	Replaced with a plausible performance-based wrong answer about computational slowness
Q12 — Fixed shard count trade-offs	Options C/D described impossible system behaviors (SSD/HDD forced by shard count; node-count ceilings of 2 or 10)	Replaced with realistic operational concerns: coordinator failover overhead and difficulty achieving fine-grained load balancing
Q17 — Risk of automated rebalancing	Options C/D described nonsensical behaviors (permanent boundary locks; DNS blocking)	Replaced with real failure modes: shard-split storms and routing tier lag during rebalancing
Q18 — Routing tier strategy	Option D described client-side RAM caching, which is not a routing strategy at all	Replaced with a push-notification shard-aware driver description that blends options A and C
Q23 — DBs that use local secondary indexes	Option C listed BigQuery/Snowflake/Delta Lake (cloud warehouses with no row-level sharding)	Replaced with CockroachDB/YugabyteDB/TiDB (distributed SQL DBs that actually use global indexes, making this a genuine knowledge test); updated option A accordingly
Q28 — DynamoDB GSI write propagation	Option D claimed weekly maintenance window updates — an obvious joke	Replaced with a 2PC-based distractor that requires knowing DynamoDB specifically avoided this approach for performance reasons

What Was Not Changed

All correct answers, explanations, write-response questions, flashcards, and MISCONCEPTION_EXPLANATIONS are unchanged. Only the wrong-answer distractor text was modified.