ReferenceIncidents
Era 3 · Series ASchema migration lock
A migration ran ALTER TABLE on the biggest table. It held the lock while it copied it, and every write queued behind it until it timed out.
What happens#
A migration ran ALTER TABLE on the biggest table. It held the lock while it copied it, and every write queued behind it until it timed out.
How to prevent it#
Online schema migrations change a big table without holding the lock.
The postmortem opens the first of these that you do not own yet: