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Jinwoo Hong
e9daf9b746
relay_control_connection_reservations was never deleted: 13.8M rows and 9.1 GB in production, 99.999% of them in state 'released' and ~400k more a day. Nothing reads a released row (every reader filters it out by state), but each placement still locks all of its host's rows, ~160 on average. A new director sweep step deletes released rows older than a day. It walks the heap in TID ranges of 16 pages, because without an index on released_at a `LIMIT n` delete plans as a sequential scan from page 0 that gets slower as the head of the heap empties (production EXPLAIN). Each statement selects its rows FOR UPDATE SKIP LOCKED, so a row a request holds is skipped rather than waited on, and deletes them by `ctid = ANY(ARRAY(...))` so the delete is always a TID scan. A tick stops at 400 rows, 128 pages or 250 ms, which drains the backlog over about three days at five directors.