Field notes from production MySQL work.
September 11, 2026
Lock wait timeouts and deadlocks are not random. Here is how to read SHOW ENGINE INNODB STATUS and the Performance Schema lock tables, what gap locks and next-key locks actually do under REPEATABLE READ, and the four fixes that hold.
Read moreSeptember 10, 2026 · QueryKings
8.0 leaves premier support in April 2026, and 8.4 is the LTS that replaces it. The version model, the direct upgrade path, the defaults that change under you (authentication, semi-sync, parallel replication), and a cutover plan with a real rollback.
Read moreAugust 18, 2026
Five distinct causes of replica lag — single-threaded apply, giant transactions, missing primary keys, starved replicas, and semi-sync effects — each with a cheap, decisive test and its actual fix.
Read moreJuly 21, 2026
INSTANT DDL, native INPLACE, gh-ost, or pt-online-schema-change? A decision tree for zero-downtime schema changes — including the metadata-lock trap that makes "non-blocking" DDL block everything.
Read moreJune 23, 2026
No downgrade path, a changed default collation, new reserved words, auth-plugin mismatches, and optimizer regressions — the checklist we run before any 5.7-to-8.0 cutover, and the replica-based shape of a safe one.
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