cleanup

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

@@ -443,8 +443,7 @@ class PostgresSaver(BasePostgresSaver):
 
         One combined UNION ALL query (`SELECT_DELTA_COMBINED_SQL`) fetches rows
         from `checkpoints`, `checkpoint_writes`, and `checkpoint_blobs` in a
-        single roundtrip. Rationale + benchmark in
-        `notes/delta_channel_query_bench.md`.
+        single roundtrip; the ancestor walk runs in Python.
         """
         thread_id = config["configurable"]["thread_id"]
         checkpoint_ns = config["configurable"].get("checkpoint_ns", "")

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

@@ -404,9 +404,8 @@ class AsyncPostgresSaver(BasePostgresSaver):
 
         One combined UNION ALL query (`SELECT_DELTA_COMBINED_SQL`) fetches rows
         from `checkpoints`, `checkpoint_writes`, and `checkpoint_blobs` in a
-        single roundtrip; rows assembled by the shared pure helper on
-        `BasePostgresSaver`. Rationale + benchmark in
-        `notes/delta_channel_query_bench.md`.
+        single roundtrip; rows are assembled by the shared pure helper on
+        `BasePostgresSaver`.
         """
         thread_id = config["configurable"]["thread_id"]
         checkpoint_ns = config["configurable"].get("checkpoint_ns", "")

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

@@ -178,12 +178,9 @@ class _DeltaCombinedRow(TypedDict, total=False):
     version: str | None
 
 
-# DeltaChannel reconstruction: one combined CTE+UNION ALL query per channel.
-# Bench (notes/delta_channel_query_bench.md) showed the prior recursive CTE
-# carried a hidden O(ancestors x blobs_in_thread) join; plain SELECTs are
-# 3x-100x faster in the realistic depth range and the Python walk is O(n).
-# The three plain SELECTs are further collapsed into one UNION ALL query so
-# that only one roundtrip is needed per channel reconstruction.
+# DeltaChannel reconstruction: one UNION ALL query fetches checkpoints,
+# writes, and blobs for `channel` in one roundtrip; the ancestor walk runs
+# in Python in `_build_delta_channel_writes_history`.
 #
 # Parameter order: (channel, thread_id, checkpoint_ns,
 #                   thread_id, checkpoint_ns, channel,
@@ -301,8 +298,7 @@ class BasePostgresSaver(BaseCheckpointSaver[str]):
                     "tuple[str, bytes]", (r["type"], r["blob"])
                 )
 
-        # Sort writes within each checkpoint (task_id DESC, idx DESC) to match
-        # the prior CTE ordering — newest write first per ancestor.
+        # newest write first per ancestor (task_id DESC, idx DESC)
         for ws in writes_by_cid.values():
             ws.sort(key=lambda w: (w[2], w[3]), reverse=True)