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fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows #4730

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fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows #4730

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4b1e803
fix(sessions): skip unnecessary FOR UPDATE lock on app/user state rows
giulio-leone Feb 28, 2026
4f2feba
refactor: simplify state delta extraction to conditional expression
giulio-leone Feb 28, 2026
8db8a51
fix: address Gemini review feedback
giulio-leone Mar 6, 2026
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20 changes: 14 additions & 6 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 @@ -536,11 +536,7 @@ async def append_event(self, session: Session, event: Event) -> Event:
is_sqlite = self.db_engine.dialect.name == _SQLITE_DIALECT
use_row_level_locking = self._supports_row_level_locking()

state_delta = (
event.actions.state_delta
if event.actions and event.actions.state_delta
else {}
)
state_delta = event.actions.state_delta if event.actions.state_delta else {}
state_deltas = _session_util.extract_state_delta(state_delta)
has_app_delta = bool(state_deltas["app"])
has_user_delta = bool(state_deltas["user"])
Expand All @@ -564,6 +560,18 @@ 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.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,
Expand Down Expand Up @@ -622,7 +630,7 @@ async def append_event(self, session: Session, event: Event) -> Event:
storage_user_state.state = (
storage_user_state.state | state_deltas["user"]
)
if state_deltas["session"]:
if state_deltas and state_deltas["session"]:
storage_session.state = (
storage_session.state | state_deltas["session"]
)
Expand Down