이코에코(Eco²) Agent Skills: Checkpointer Reference

Chat Agent Persistence Skill.md 하위 Reference
Cache Aside 패턴 및 LangGraph 멀티턴 대화 컨텍스트 영속화 명시

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                    Cache-Aside Pattern                           │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│  조회 (aget_tuple)                                               │
│  ─────────────────                                               │
│  LangGraph → Redis (L1, ~1ms)                                    │
│                 │                                                │
│                 ├── Hit → Return                                 │
│                 │                                                │
│                 └── Miss → PostgreSQL (L2)                       │
│                               │                                  │
│                               └── Redis 캐싱 (warm-up)           │
│                                       │                          │
│                                       └── Return                 │
│                                                                  │
│  저장 (aput)                                                     │
│  ───────────                                                     │
│  LangGraph → PostgreSQL (영구) + Redis (캐시)                     │
│              Write-Through                                       │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

Components

Class	Purpose	Layer
CachedPostgresSaver	L1 Redis + L2 PostgreSQL	Adapter
AsyncPostgresSaver	LangGraph PostgreSQL 체크포인터	External (langgraph)
MemorySaver	In-memory fallback	External (langgraph)

Current Issue

Error

[WARNING] CachedPostgresSaver failed, falling back to Redis only:
object _AsyncGeneratorContextManager can't be used in 'await' expression

Root Cause

checkpointer.py:228:

# BUG: from_conn_string()은 async context manager 반환
postgres_saver = await AsyncPostgresSaver.from_conn_string(conn_string)  # WRONG!

LangGraph API Signature

# langgraph-checkpoint-postgres
class AsyncPostgresSaver:
    @classmethod
    @asynccontextmanager
    async def from_conn_string(cls, conn_string: str) -> AsyncIterator["AsyncPostgresSaver"]:
        """Async context manager - await 아님!"""
        ...

Fallback Chain

CachedPostgresSaver (PostgreSQL + Redis)
       │
       │ Exception
       ▼
create_redis_checkpointer()
       │
       │ (Redis checkpointer도 lifecycle 이슈)
       ▼
MemorySaver (In-memory only)

Fix Options

Option A: Context Manager 수동 관리

class CachedPostgresSaver(BaseCheckpointSaver):
    _postgres_cm: AsyncContextManager | None = None

    @classmethod
    async def create(cls, conn_string: str, redis: "Redis") -> "CachedPostgresSaver":
        from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver

        cm = AsyncPostgresSaver.from_conn_string(conn_string)
        postgres_saver = await cm.__aenter__()

        instance = cls(postgres_saver=postgres_saver, redis=redis)
        instance._postgres_cm = cm
        return instance

    async def close(self) -> None:
        if self._postgres_cm:
            await self._postgres_cm.__aexit__(None, None, None)

Option B: Connection Pool 직접 생성 (권장)

from psycopg_pool import AsyncConnectionPool

async def create_cached_postgres_checkpointer(
    conn_string: str,
    redis: "Redis",
) -> CachedPostgresSaver:
    from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver

    # Pool 직접 생성
    pool = AsyncConnectionPool(conninfo=conn_string)
    await pool.open()

    postgres_saver = AsyncPostgresSaver(pool)
    await postgres_saver.setup()  # 테이블 생성

    return CachedPostgresSaver(
        postgres_saver=postgres_saver,
        redis=redis,
        pool=pool,  # cleanup 위해 보관
    )

Verification

# 1. Worker 로그에서 성공 메시지 확인
kubectl logs -n chat deploy/chat-worker --tail=50 | grep -E "CachedPostgresSaver (created|initialized)"

# 2. PostgreSQL 체크포인트 테이블 확인
kubectl exec -n postgres deploy/postgresql -- psql -U sesacthon -d ecoeco -c \
  "SELECT COUNT(*) FROM checkpoints;"

# 3. 멀티턴 대화 테스트
# 첫 번째 메시지: "내 이름은 철수야"
# 두 번째 메시지: "내 이름이 뭐라고 했지?" → 철수 기억하면 성공

Configuration

Variable	Value	Description
POSTGRES_URL	postgresql+asyncpg://...	PostgreSQL 연결 문자열
REDIS_URL	redis://rfr-pubsub-redis-0...	Redis 캐시 URL
Cache TTL	86400 (24h)	체크포인트 캐시 TTL

Related Files

File	Description
checkpointer.py	CachedPostgresSaver 구현
dependencies.py:641-678	get_checkpointer() 함수
factory.py	Graph 생성 시 checkpointer 주입