An index on (created_at, status) serving a query that filters on status and ranges on date, which uses the first column and stops. The rule is equality columns…
ALGORITHM=INPLACE does not mean lock-free, and the operation that needed a table rebuild took a metadata lock at the end anyway. Specifying LOCK=NONE turns an unpleasant surprise into…
Replication lag of eleven minutes on a replica with no load, caused by a single transaction on the primary that took eleven minutes. The instant drop is the…
Adding a nullable column is instant in 8.0; filling it for four million existing rows is not. Three steps instead of one — add nullable, backfill, tighten —…
Every page load unserialising four hundred kilobytes of a plugin’s cached API response, because it had been stored as an autoloaded option. Autoloaded options are read as one…