MySQL
3 engineering logs on MySQL. Newest first.
- ADD COLUMN is not always free, and the lock queue is what takes you down
Why a metadata-only migration still took the site offline for forty minutes, how a waiting ALTER blocks every query behind it, and why lock_timeout is the setting that turns a migration into a retry.
- Why your index is not being used, and why the planner is usually right
The index exists and EXPLAIN still says sequential scan. A field guide to sargability, stale statistics, the leftmost prefix rule, and the cost settings that make a planner reject an index it should have chosen.
- Why UUID Primary Keys Quietly Destroy Database Performance
How random UUID primary keys break clustered indexes, cause page splits and buffer pool churn, and what to use instead for mechanically sympathetic database design.