checkpoint-postgres: remove pipeline flag in cursor

libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py

@@ -1,5 +1,5 @@
 import asyncio
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, nullcontext
 from typing import Any, AsyncIterator, Iterator, Optional, Sequence, Union
 
 from langchain_core.runnables import RunnableConfig
@@ -264,28 +264,29 @@ class AsyncPostgresSaver(BasePostgresSaver):
             }
         }
 
-        async with self._cursor(pipeline=True) as cur:
-            await cur.executemany(
-                self.UPSERT_CHECKPOINT_BLOBS_SQL,
-                await asyncio.to_thread(
-                    self._dump_blobs,
-                    thread_id,
-                    checkpoint_ns,
-                    copy.pop("channel_values"),  # type: ignore[misc]
-                    new_versions,
-                ),
-            )
-            await cur.execute(
-                self.UPSERT_CHECKPOINTS_SQL,
-                (
-                    thread_id,
-                    checkpoint_ns,
-                    checkpoint["id"],
-                    checkpoint_id,
-                    Jsonb(self._dump_checkpoint(copy)),
-                    self._dump_metadata(metadata),
-                ),
-            )
+        async with self._cursor() as cur:
+            async with cur.connection.transaction() if self.pipe is None else nullcontext():
+                await cur.executemany(
+                    self.UPSERT_CHECKPOINT_BLOBS_SQL,
+                    await asyncio.to_thread(
+                        self._dump_blobs,
+                        thread_id,
+                        checkpoint_ns,
+                        copy.pop("channel_values"),  # type: ignore[misc]
+                        new_versions,
+                    ),
+                )
+                await cur.execute(
+                    self.UPSERT_CHECKPOINTS_SQL,
+                    (
+                        thread_id,
+                        checkpoint_ns,
+                        checkpoint["id"],
+                        checkpoint_id,
+                        Jsonb(self._dump_checkpoint(copy)),
+                        self._dump_metadata(metadata),
+                    ),
+                )
         return next_config
 
     async def aput_writes(
@@ -316,13 +317,11 @@ class AsyncPostgresSaver(BasePostgresSaver):
             task_id,
             writes,
         )
-        async with self._cursor(pipeline=True) as cur:
+        async with self._cursor() as cur:
             await cur.executemany(query, params)
 
     @asynccontextmanager
-    async def _cursor(
-        self, *, pipeline: bool = False
-    ) -> AsyncIterator[AsyncCursor[DictRow]]:
+    async def _cursor(self) -> AsyncIterator[AsyncCursor[DictRow]]:
         async with _get_connection(self.conn) as conn:
             if self.pipe:
                 # a connection in pipeline mode can be used concurrently
@@ -332,15 +331,7 @@ class AsyncPostgresSaver(BasePostgresSaver):
                     async with conn.cursor(binary=True, row_factory=dict_row) as cur:
                         yield cur
                 finally:
-                    if pipeline:
-                        await self.pipe.sync()
-            elif pipeline:
-                # a connection not in pipeline mode can only be used by one
-                # thread/coroutine at a time, so we acquire a lock
-                async with self.lock, conn.pipeline(), conn.cursor(
-                    binary=True, row_factory=dict_row
-                ) as cur:
-                    yield cur
+                    await self.pipe.sync()
             else:
                 async with self.lock, conn.cursor(
                     binary=True, row_factory=dict_row