X_DB_UNIQUE_VIOLATION
Means
a unique constraint rejected the row
Typical cause
SQLSTATE 23505 — two clicks racing a signup, or an insert where an upsert was meant. One of six driver failures that used to reach the caller as X_DB_UNAVAILABLE, whose fix reads "set DATABASE_URL to a reachable Postgres": a raced signup paged on-call for an outage that never happened. meta.constraint names the index the server refused on
Fix
upsertAll(rows, { onConflict: [...] }) over the columns the constraint cause names — or catch X_DB_UNIQUE_VIOLATION and answer 409, which is what a raced signup is