Field notes from production MySQL work.
August 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.
Read moreMay 19, 2026
Seven rules we apply on schema audits: design for the query shape, respect the leftmost prefix and the clustered index, make hot queries covering, and prune with invisible indexes before dropping.
Read moreApril 14, 2026
How we actually read a query plan in a tuning engagement: the columns that carry signal, the traps in Extra, join-order reasoning, and a worked example that took p99 from 1.8s to 4ms.
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