From 086268da1ca43a85eccc63228aec6b81f6bee74d Mon Sep 17 00:00:00 2001
From: hjh79gw <hjh79gw@gmail.com>
Date: Mon, 18 May 2026 10:49:57 +0900
Subject: [PATCH] feat(w03): stage1 schema and session code

---
 .../src/main/resources/Stage1Manual.sql       | 108 ++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 topics/03-lock/members/jaehoon/src/main/resources/Stage1Manual.sql

diff --git a/topics/03-lock/members/jaehoon/src/main/resources/Stage1Manual.sql b/topics/03-lock/members/jaehoon/src/main/resources/Stage1Manual.sql
new file mode 100644
index 0000000..bfa484b
--- /dev/null
+++ b/topics/03-lock/members/jaehoon/src/main/resources/Stage1Manual.sql
@@ -0,0 +1,108 @@
+-- 3주차 stage 1 환전
+
+--셋팅
+docker exec -it csstudy-postgres psql -U csstudy -d csstudy
+SELECT pg_backend_pid();
+
+-- 테이블
+CREATE TABLE IF NOT EXISTS wallet03 (
+    user_id  BIGINT NOT NULL,
+    currency VARCHAR(3) NOT NULL,
+    balance  BIGINT NOT NULL,
+    version  BIGINT NOT NULL DEFAULT 0,
+    PRIMARY KEY (user_id, currency)
+);
+INSERT INTO wallet03 (user_id, currency, balance) VALUES (1, 'KRW', 1000000), (1, 'USD', 1000)
+ON CONFLICT (user_id, currency) DO UPDATE SET balance = EXCLUDED.balance, version = 0;
+
+
+
+
+-- 1-1 SELECT FOR UPDATE
+-- FOR UPDATE가 다른 세션을 어떻게 막는 지
+
+-- 세션 A
+BEGIN;
+SELECT * FROM wallet03 WHERE user_id = 1 AND currency = 'KRW' FOR UPDATE;
+-- A가 KRW row에 X-lock 획득. 여기서 멈추고 세션 B로 이동.
+
+-- 세션 B
+-- 1. SELECT (MVCC lock-free라 안 막힘)
+SELECT * FROM wallet03 WHERE user_id = 1 AND currency = 'KRW';
+
+-- 2. UPDATE (X-lock 대기)
+UPDATE wallet03 SET balance = 50000 WHERE user_id = 1 AND currency = 'KRW';
+
+-- 3. FOR UPDATE (X-lock 대기)
+SELECT * FROM wallet03 WHERE user_id = 1 AND currency = 'KRW' FOR UPDATE;
+
+-- 4. FOR SHARE (S-lock 차단)
+SELECT * FROM wallet03 WHERE user_id = 1 AND currency = 'KRW' FOR SHARE;
+
+-- 세션 A
+COMMIT;
+
+
+
+
+-- 1-2. 데드락
+
+-- 두 row를 다른 순서로 잡음
+UPDATE wallet03 SET balance = 1000000, version = 0 WHERE user_id = 1 AND currency = 'KRW';
+UPDATE wallet03 SET balance = 1000, version = 0 WHERE user_id = 1 AND currency = 'USD';
+
+-- 세션 A (KRW 먼저 잡기)
+BEGIN;
+UPDATE wallet03 SET balance = balance - 1000 WHERE user_id = 1 AND currency = 'KRW';
+
+
+-- 세션 B (USD 먼저 잡기)
+BEGIN;
+UPDATE wallet03 SET balance = balance - 1 WHERE user_id = 1 AND currency = 'USD';
+-- USD row에 X-lock 획득. 여기서 멈추고 세션 A로 이동.
+
+-- 세션 A (USD lock 시도 - B가 잡고 있어서 대기)
+UPDATE wallet03 SET balance = balance + 1 WHERE user_id = 1 AND currency = 'USD';
+
+-- 세션 B (KRW lock 시도 - A가 잡고 있어서 대기 - 순환 대기 - 데드락)
+UPDATE wallet03 SET balance = balance + 1000 WHERE user_id = 1 AND currency = 'KRW';
+
+-- Coffman 4조건
+-- 1. 상호 배제: row X-lock은 한 tx만 보유 가능
+-- 2. 점유 대기: A가 KRW lock 잡은 채로 USD lock 기다림
+-- 3. 비선점: B의 USD lock을 A가 강제로 뺏을 수 없음
+-- 4. 순환 대기: A->B(USD 기다림)->A(KRW 기다림) 순환
+
+
+COMMIT;
+ROLLBACK;
+
+
+-- 1-3. Redis 분산락
+docker exec -it csstudy-redis redis-cli
+
+-- 창 A: 잠금 시도
+SET lock:wallet03:1:exchange "session-A" NX EX 10
+
+-- 창 B: 같은 키 잠금 시도
+SET lock:wallet03:1:exchange "session-B" NX EX 10
+
+-- 창 A: 해제
+DEL lock:wallet03:1:exchange
+
+-- 창 B: 재시도
+SET lock:wallet03:1:exchange "session-B" NX EX 10
+
+
+-- 1-4. 현재 락 상태 확인
+
+SELECT
+    pid,
+    locktype,
+    relation::regclass AS table_name,
+    mode,
+    granted
+FROM pg_locks
+WHERE relation IS NOT NULL
+  AND relation::regclass::text = 'wallet03'
+ORDER BY pid;