fix(runtime): avoid postgres aggregate row lock (#2962)

backend/packages/harness/deerflow/runtime/events/store/db.py

@@ -11,7 +11,7 @@ import logging
 from datetime import UTC, datetime
 from typing import Any
 
-from sqlalchemy import delete, func, select
+from sqlalchemy import delete, func, select, text
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 
 from deerflow.persistence.models.run_event import RunEventRow
@@ -86,6 +86,28 @@ class DbRunEventStore(RunEventStore):
         user = get_current_user()
         return str(user.id) if user is not None else None
 
+    @staticmethod
+    async def _max_seq_for_thread(session: AsyncSession, thread_id: str) -> int | None:
+        """Return the current max seq while serializing writers per thread.
+
+        PostgreSQL rejects ``SELECT max(...) FOR UPDATE`` because aggregate
+        results are not lockable rows. As a release-safe workaround, take a
+        transaction-level advisory lock keyed by thread_id before reading the
+        aggregate. Other dialects keep the existing row-locking statement.
+        """
+        stmt = select(func.max(RunEventRow.seq)).where(RunEventRow.thread_id == thread_id)
+        bind = session.get_bind()
+        dialect_name = bind.dialect.name if bind is not None else ""
+
+        if dialect_name == "postgresql":
+            await session.execute(
+                text("SELECT pg_advisory_xact_lock(hashtext(CAST(:thread_id AS text))::bigint)"),
+                {"thread_id": thread_id},
+            )
+            return await session.scalar(stmt)
+
+        return await session.scalar(stmt.with_for_update())
+
     async def put(self, *, thread_id, run_id, event_type, category, content="", metadata=None, created_at=None):  # noqa: D401
         """Write a single event — low-frequency path only.
 
@@ -100,10 +122,7 @@ class DbRunEventStore(RunEventStore):
         user_id = self._user_id_from_context()
         async with self._sf() as session:
             async with session.begin():
-                # Use FOR UPDATE to serialize seq assignment within a thread.
-                # NOTE: with_for_update() on aggregates is a no-op on SQLite;
-                # the UNIQUE(thread_id, seq) constraint catches races there.
-                max_seq = await session.scalar(select(func.max(RunEventRow.seq)).where(RunEventRow.thread_id == thread_id).with_for_update())
+                max_seq = await self._max_seq_for_thread(session, thread_id)
                 seq = (max_seq or 0) + 1
                 row = RunEventRow(
                     thread_id=thread_id,
@@ -126,10 +145,8 @@ class DbRunEventStore(RunEventStore):
         async with self._sf() as session:
             async with session.begin():
                 # Get max seq for the thread (assume all events in batch belong to same thread).
-                # NOTE: with_for_update() on aggregates is a no-op on SQLite;
-                # the UNIQUE(thread_id, seq) constraint catches races there.
                 thread_id = events[0]["thread_id"]
-                max_seq = await session.scalar(select(func.max(RunEventRow.seq)).where(RunEventRow.thread_id == thread_id).with_for_update())
+                max_seq = await self._max_seq_for_thread(session, thread_id)
                 seq = max_seq or 0
                 rows = []
                 for e in events: