[calmcoconut]

Summary

Replaces obviously wrong or absurd MCQ distractors in Chapter 4 with more plausible technical alternatives, making questions harder to solve by elimination alone.

Problem

About 12 of the 18 MCQs had at least one distractor that was so clearly fabricated or off-topic that a test-taker could narrow down the correct answer without understanding the material. Examples: "holographic storage drive", "PNG compression on column data", "XML schemas for columnar storage", "tape drive backup for reverse ETL".

Changes (learning-app/ch04/app.js)

Question	Old (weak) distractor	New (plausible) distractor
SSTables vs append-only log	"fits in OS page memory cache"	"enables parallel reads across independent I/O streams"
Bloom filters	"pre-sorts keys in heap memory before memtable flush"	"caches recently read SSTable blocks to reduce disk seeks"
B-tree key abbreviation	"encrypts sensitive keys before cloud storage"	"allows leaf pages to store more sorted entries per disk block"
Covering index	"monitors foreign keys to prevent join latency"	"automatically kept synchronized with the primary index"
Lucene fuzzy search	"pre-computed hash map of all word-pair edit distances"	"trie BFS branching at each permitted edit"
ELT vs ETL (option C)	"ELT relies on NoSQL; reverse ETL replicates B-tree index files"	"ELT loads into staging area outside warehouse before ingestion"
ELT vs ETL (option D)	"real-time streaming protocol; backs up to tape drives"	"ELT and ETL are identical; distinction only matters for legacy Hadoop"
Columnar storage layout	"append-only XML schemas"	"columns co-located in same physical row group"
Bitmap encoding	"PNG compression on column data"	"dictionary encoding with variable-length integer codes"
OLAP data cube (option A)	"3D holographic storage drive"	"multi-dimensional index pre-sorting dimension key ranges"
OLAP data cube (option D)	"replicates to exactly six adjacent servers"	"distributed cache materializing per-partition partial aggregates"
B-trees and 2D spatial data (option A)	"B-trees can't sort floats"	"spatial coords must be flattened via space-filling curve"
B-trees and 2D spatial data (option C)	"B-trees only sort alphanumeric strings"	"B-trees must rebuild branching structure on coordinate updates"
B-tree latches (option D)	"links index pages across distributed cluster"	"guarantees transaction changes are durable before commit"
Copy-on-write B-trees (option A)	"Page-overlay B-tree configurations"	"Fractional cascading B-trees"

No logic changes

All correct index values, explanation text, write-in questions, flashcards, and all other app logic are unchanged.