Remove Checkpoint.pending_sends

- Instead store sends in a Topic channel, removing the need to fetch sends as writes against the parent checkpoint
- Remove deprecated/unused functions in langgraph-checkpoint (will require bumping min range for langgraph-checkpoint in langgraph lib)
- Implement migration of old pending sends in langgraph-checkpoint-postgres
- Ensure parent config of `checkpoint_during=False` checkpoints always points to checkpoints that were also saved

libs/checkpoint-sqlite/README.md

@@ -12,7 +12,7 @@ read_config = {"configurable": {"thread_id": "1"}}
 
 with SqliteSaver.from_conn_string(":memory:") as checkpointer:
     checkpoint = {
-        "v": 2,
+        "v": 4,
         "ts": "2024-07-31T20:14:19.804150+00:00",
         "id": "1ef4f797-8335-6428-8001-8a1503f9b875",
         "channel_values": {
@@ -34,7 +34,6 @@ with SqliteSaver.from_conn_string(":memory:") as checkpointer:
                 "start:node": 2
             }
         },
-        "pending_sends": [],
     }
 
     # store checkpoint
@@ -54,7 +53,7 @@ from langgraph.checkpoint.sqlite.aio import AsyncSqliteSaver
 
 async with AsyncSqliteSaver.from_conn_string(":memory:") as checkpointer:
     checkpoint = {
-        "v": 2,
+        "v": 4,
         "ts": "2024-07-31T20:14:19.804150+00:00",
         "id": "1ef4f797-8335-6428-8001-8a1503f9b875",
         "channel_values": {
@@ -76,7 +75,6 @@ async with AsyncSqliteSaver.from_conn_string(":memory:") as checkpointer:
                 "start:node": 2
             }
         },
-        "pending_sends": [],
     }
 
     # store checkpoint

libs/checkpoint-sqlite/langgraph/checkpoint/sqlite/__init__.py

@@ -19,7 +19,6 @@ from langgraph.checkpoint.base import (
     get_checkpoint_metadata,
 )
 from langgraph.checkpoint.serde.jsonplus import JsonPlusSerializer
-from langgraph.checkpoint.serde.types import ChannelProtocol
 from langgraph.checkpoint.sqlite.utils import search_where
 
 _AIO_ERROR_MSG = (
@@ -535,14 +534,13 @@ class SqliteSaver(BaseCheckpointSaver[str]):
         """
         raise NotImplementedError(_AIO_ERROR_MSG)
 
-    def get_next_version(self, current: Optional[str], channel: ChannelProtocol) -> str:
+    def get_next_version(self, current: Optional[str]) -> str:
         """Generate the next version ID for a channel.
 
         This method creates a new version identifier for a channel based on its current version.
 
         Args:
             current (Optional[str]): The current version identifier of the channel.
-            channel (BaseChannel): The channel being versioned.
 
         Returns:
             str: The next version identifier, which is guaranteed to be monotonically increasing.

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

@@ -19,7 +19,6 @@ from langgraph.checkpoint.base import (
     get_checkpoint_metadata,
 )
 from langgraph.checkpoint.serde.jsonplus import JsonPlusSerializer
-from langgraph.checkpoint.serde.types import ChannelProtocol
 from langgraph.checkpoint.sqlite.utils import search_where
 
 T = TypeVar("T", bound=Callable)
@@ -590,14 +589,13 @@ class AsyncSqliteSaver(BaseCheckpointSaver[str]):
             )
             await self.conn.commit()
 
-    def get_next_version(self, current: Optional[str], channel: ChannelProtocol) -> str:
+    def get_next_version(self, current: Optional[str]) -> str:
         """Generate the next version ID for a channel.
 
         This method creates a new version identifier for a channel based on its current version.
 
         Args:
             current (Optional[str]): The current version identifier of the channel.
-            channel (BaseChannel): The channel being versioned.
 
         Returns:
             str: The next version identifier, which is guaranteed to be monotonically increasing.

libs/checkpoint-sqlite/tests/checkpoint_utils.py

@@ -0,0 +1,51 @@
+from collections.abc import Mapping
+from datetime import datetime, timezone
+from typing import Any, Optional, Protocol
+
+from langgraph.checkpoint.base import Checkpoint, EmptyChannelError
+from langgraph.checkpoint.base.id import uuid6
+
+
+class ChannelProtocol(Protocol):
+    def checkpoint(self) -> Optional[Any]: ...
+
+
+def empty_checkpoint() -> Checkpoint:
+    return Checkpoint(
+        v=1,
+        id=str(uuid6(clock_seq=-2)),
+        ts=datetime.now(timezone.utc).isoformat(),
+        channel_values={},
+        channel_versions={},
+        versions_seen={},
+    )
+
+
+def create_checkpoint(
+    checkpoint: Checkpoint,
+    channels: Optional[Mapping[str, ChannelProtocol]],
+    step: int,
+    *,
+    id: Optional[str] = None,
+) -> Checkpoint:
+    """Create a checkpoint for the given channels."""
+    ts = datetime.now(timezone.utc).isoformat()
+    if channels is None:
+        values = checkpoint["channel_values"]
+    else:
+        values = {}
+        for k, v in channels.items():
+            if k not in checkpoint["channel_versions"]:
+                continue
+            try:
+                values[k] = v.checkpoint()
+            except EmptyChannelError:
+                pass
+    return Checkpoint(
+        v=1,
+        ts=ts,
+        id=id or str(uuid6(clock_seq=step)),
+        channel_values=values,
+        channel_versions=checkpoint["channel_versions"],
+        versions_seen=checkpoint["versions_seen"],
+    )

libs/checkpoint-sqlite/tests/test_aiosqlite.py

@@ -6,10 +6,9 @@ from langchain_core.runnables import RunnableConfig
 from langgraph.checkpoint.base import (
     Checkpoint,
     CheckpointMetadata,
-    create_checkpoint,
-    empty_checkpoint,
 )
 from langgraph.checkpoint.sqlite.aio import AsyncSqliteSaver
+from tests.checkpoint_utils import create_checkpoint, empty_checkpoint
 
 
 class TestAsyncSqliteSaver:

libs/checkpoint-sqlite/tests/test_sqlite.py

@@ -6,11 +6,10 @@ from langchain_core.runnables import RunnableConfig
 from langgraph.checkpoint.base import (
     Checkpoint,
     CheckpointMetadata,
-    create_checkpoint,
-    empty_checkpoint,
 )
 from langgraph.checkpoint.sqlite import SqliteSaver
 from langgraph.checkpoint.sqlite.utils import _metadata_predicate, search_where
+from tests.checkpoint_utils import create_checkpoint, empty_checkpoint
 
 
 class TestSqliteSaver: