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fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows #4656

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fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows #4656

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72694a7
fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows
giulio-leone Feb 28, 2026
2abcbdf
refactor: simplify state delta extraction to conditional expression
giulio-leone Feb 28, 2026
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23 changes: 16 additions & 7 deletions src/google/adk/sessions/database_session_service.py
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Original file line number Diff line number Diff line change
Expand Up @@ -550,11 +550,23 @@ async def append_event(self, session: Session, event: Event) -> Event:
if storage_session is None:
raise ValueError(f"Session {session.id} not found.")

# Pre-analyze state deltas to determine which scopes actually need
# write locks. Most events carry only session-scoped state (or no
# state at all), so acquiring FOR UPDATE on app_states / user_states
# unnecessarily serializes all concurrent append_event calls.
state_deltas = (
_session_util.extract_state_delta(event.actions.state_delta)
if event.actions and event.actions.state_delta
else None
)
has_app_delta = bool(state_deltas and state_deltas.get("app"))
has_user_delta = bool(state_deltas and state_deltas.get("user"))

storage_app_state = await _select_required_state(
sql_session=sql_session,
state_model=schema.StorageAppState,
predicates=(schema.StorageAppState.app_name == session.app_name,),
use_row_level_locking=use_row_level_locking,
use_row_level_locking=use_row_level_locking and has_app_delta,
missing_message=(
"App state missing for app_name="
f"{session.app_name!r}. Session state tables should be "
Expand All @@ -568,7 +580,7 @@ async def append_event(self, session: Session, event: Event) -> Event:
schema.StorageUserState.app_name == session.app_name,
schema.StorageUserState.user_id == session.user_id,
),
use_row_level_locking=use_row_level_locking,
use_row_level_locking=use_row_level_locking and has_user_delta,
missing_message=(
"User state missing for app_name="
f"{session.app_name!r}, user_id={session.user_id!r}. "
Expand Down Expand Up @@ -599,11 +611,8 @@ async def append_event(self, session: Session, event: Event) -> Event:
storage_events = [e async for e in result]
session.events = [e.to_event() for e in storage_events]

# Extract state delta
if event.actions and event.actions.state_delta:
state_deltas = _session_util.extract_state_delta(
event.actions.state_delta
)
# Apply state deltas (already extracted above for lock scoping)
if state_deltas is not None:
app_state_delta = state_deltas["app"]
user_state_delta = state_deltas["user"]
session_state_delta = state_deltas["session"]
Expand Down