hyungi_document_server/migrations/117_queue_active_unique.sql

-- Step 1: stale duplicate 삭제 (processing 10분+ 방치 + 같은 doc/stage에 pending 존재)
DELETE FROM processing_queue a
USING processing_queue b
WHERE a.document_id = b.document_id
  AND a.stage = b.stage
  AND a.status = 'processing'
  AND a.started_at < NOW() - INTERVAL '10 minutes'
  AND b.status = 'pending';

-- Step 2: 기존 constraint 제거
ALTER TABLE processing_queue
    DROP CONSTRAINT processing_queue_document_id_stage_status_key;

-- Step 3: partial unique index (활성 행은 (document_id, stage)당 최대 1개)
-- 활성 중복이 남아있으면 여기서 자연스럽게 실패 → 수동 정리 후 재시도
CREATE UNIQUE INDEX uq_queue_active
    ON processing_queue (document_id, stage)
    WHERE status IN ('pending', 'processing');