회기 연속성과 멀티 케이스 계약을 영속화

infra/db/init/21_single_active_session.sql

@@ -0,0 +1,87 @@
+-- =============================================================================
+-- Vignette · migration 21 — learner-persona별 단일 활성 회기
+-- =============================================================================
+-- 기존 DB 적용 전 owner가 아래 읽기 전용 점검을 실행한다.
+-- 중복 또는 실패 후 남은 invalid index가 있으면 임의 종료·DROP 하지 말고
+-- 소유자가 보존·복구 방식을 결정해야 한다.
+--
+-- SELECT learner_id, persona_id, count(*)
+-- FROM app.sessions
+-- WHERE ended_at IS NULL AND persona_id IS NOT NULL
+-- GROUP BY learner_id, persona_id
+-- HAVING count(*) > 1;
+--
+-- CREATE INDEX CONCURRENTLY는 transaction block 안에서 실행할 수 없다.
+-- release agent가 online migration으로 owner psql에 전달한다.
+-- 이 파일의 전·후 condition은 IF NOT EXISTS가 invalid/wrong index를 조용히
+-- 건너뛰는 경우를 fail-closed로 막는다.
+
+DO $$
+DECLARE
+  target_index oid := to_regclass('app.uq_sessions_one_active_learner_persona');
+BEGIN
+  IF EXISTS (
+    SELECT 1
+    FROM app.sessions
+    WHERE ended_at IS NULL
+      AND persona_id IS NOT NULL
+    GROUP BY learner_id, persona_id
+    HAVING count(*) > 1
+  ) THEN
+    RAISE EXCEPTION
+      'migration 21 blocked: duplicate active learner-persona sessions exist';
+  END IF;
+
+  IF target_index IS NOT NULL AND NOT EXISTS (
+    SELECT 1
+    FROM pg_index AS index_meta
+    WHERE index_meta.indexrelid = target_index
+      AND index_meta.indrelid = 'app.sessions'::regclass
+      AND index_meta.indisvalid
+      AND index_meta.indisready
+      AND index_meta.indisunique
+      AND index_meta.indnkeyatts = 2
+      AND pg_get_indexdef(index_meta.indexrelid, 1, true) = 'learner_id'
+      AND pg_get_indexdef(index_meta.indexrelid, 2, true) = 'persona_id'
+      AND regexp_replace(
+        pg_get_expr(index_meta.indpred, index_meta.indrelid),
+        '[[:space:]()]',
+        '',
+        'g'
+      ) = 'ended_atISNULLANDpersona_idISNOTNULL'
+  ) THEN
+    RAISE EXCEPTION
+      'migration 21 blocked: target index exists but is invalid or has a different definition';
+  END IF;
+END
+$$;
+
+CREATE UNIQUE INDEX CONCURRENTLY IF NOT EXISTS uq_sessions_one_active_learner_persona
+  ON app.sessions (learner_id, persona_id)
+  WHERE ended_at IS NULL AND persona_id IS NOT NULL;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1
+    FROM pg_index AS index_meta
+    WHERE index_meta.indexrelid = 'app.uq_sessions_one_active_learner_persona'::regclass
+      AND index_meta.indrelid = 'app.sessions'::regclass
+      AND index_meta.indisvalid
+      AND index_meta.indisready
+      AND index_meta.indisunique
+      AND index_meta.indnkeyatts = 2
+      AND pg_get_indexdef(index_meta.indexrelid, 1, true) = 'learner_id'
+      AND pg_get_indexdef(index_meta.indexrelid, 2, true) = 'persona_id'
+      AND regexp_replace(
+        pg_get_expr(index_meta.indpred, index_meta.indrelid),
+        '[[:space:]()]',
+        '',
+        'g'
+      ) = 'ended_atISNULLANDpersona_idISNOTNULL'
+  ) THEN
+    RAISE EXCEPTION
+      'migration 21 failed: valid target unique index was not created';
+  END IF;
+END
+$$;