PostgreSQL refuses DROP DATABASE while any session is connected:
ERROR: database "picpeak_prod" is being accessed by other users
DETAIL: There are 6 other sessions using the database.
The backend's own knex pool holds 5-25 active connections to the
target DB. So even after closing the request that initiated the
restore, the pool keeps the DB busy and the DROP statement fails.
Three-layered cure, all in the restore service's PG branch:
1. Call `db.destroy()` first to close the in-process knex pool so
we don't fight ourselves. Knex will lazily re-open on the next
query via db.js's retry logic, so this is safe to do mid-restore.
2. SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE
datname=<target> AND pid<>pg_backend_pid() — evicts any sessions
from other processes (other server replicas, leftover idle
transactions, things our own pool destroy missed).
3. DROP DATABASE IF EXISTS "<target>" WITH (FORCE) — PG13+ kills
remaining connections atomically with the DROP. Falls back to
plain DROP on older Postgres where WITH (FORCE) is a syntax error.
Surfaced as the FIFTH latent bug in the restore path tonight: the
DROP DATABASE statement always assumed a quiescent destination, but
the live backend keeps the destination busy at all times. Every
previous PG install of picpeak that ever tried Restore would have
hit this — meaning the disaster-recovery feature has shipped broken
for a long time without anyone exercising it end-to-end.
Luca
a39def672e