[BLCCoreStudio]

Summary

Upgrades database/mysql from a compact schema-v1 overview into a schema-v3 deep technical reference centered on MySQL's real server/storage boundary and InnoDB operational model.

Changes

• explain the SQL layer, pluggable storage-engine interface, and InnoDB architecture
• cover clustered/secondary indexes, buffer-pool behavior, redo/undo, MVCC, isolation, next-key locking, deadlocks, and transaction retries
• document optimizer statistics, histograms, EXPLAIN, composite-index trade-offs, online/atomic DDL caveats, and metadata locking
• add binary-log semantics, GTIDs, source/replica replication, Group Replication, and InnoDB Cluster boundaries
• add backup, PITR, restore testing, durability-vs-replication distinctions, and HA failure semantics
• cover accounts, roles, TLS, definer-context objects, Performance Schema, capacity planning, incident triage, and common production failure modes
• upgrade metadata to schema v3 with GPL Community Edition licensing, deployment facets, Technology Universe coverage, and typed alternatives to PostgreSQL and SQLite
• expand the curated source set using official MySQL documentation and the canonical server repository

Quality bar

The module treats MySQL as a layered SQL server plus InnoDB transaction/storage system, not as a feature list. It makes redo/undo/binlog boundaries, clustered-index consequences, MVCC/locking behavior, replication lag, backup recovery, HA routing, and operational failure diagnosis explicit enough to reason about production systems.