DatabaseSessionService.get_session returns all events when num_recent_events=0

🔴 Required Information

Describe the Bug:

DatabaseSessionService.get_session(..., config=GetSessionConfig(num_recent_events=0)) is documented to return no events (see GetSessionConfig docstring in src/google/adk/sessions/base_session_service.py: "if 0, no events are returned").

However, when num_recent_events=0 is passed, all events of the session are returned instead of an empty list.

This appears to be caused by a truthy check on num_recent_events in src/google/adk/sessions/database_session_service.py (around line 523):

if config and config.num_recent_events:          # ← `0` is falsy, so this branch is skipped
    stmt = stmt.limit(config.num_recent_events)

Because 0 is falsy in Python, the LIMIT clause is never appended when num_recent_events=0, and the query returns every event for the session.

The other in-tree implementations appear to handle 0 correctly:

InMemorySessionService (src/google/adk/sessions/in_memory_session_service.py:204-211): uses is not None and explicitly assigns events = [] when num_recent_events == 0.
SqliteSessionService (src/google/adk/sessions/sqlite_session_service.py:264-271): uses is not None for the LIMIT clause, plus an explicit early return for == 0.

So this issue appears to be specific to DatabaseSessionService (SQLAlchemy backend).

Steps to Reproduce:

Install google-adk (reproduced on 1.33.0 / current main) and aiosqlite.
Run the following script (uses SQLite in-memory, no external DB needed):

import asyncio
from google.genai import types
from google.adk.events.event import Event
from google.adk.sessions.base_session_service import GetSessionConfig
from google.adk.sessions.database_session_service import DatabaseSessionService

async def main():
    svc = DatabaseSessionService(db_url="sqlite+aiosqlite:///:memory:")
    app, user, sid = "app", "user_1", "session_1"

    session = await svc.create_session(app_name=app, user_id=user, session_id=sid)

    for i in range(5):
        ev = Event(
            invocation_id=f"inv_{i}",
            author="user" if i % 2 == 0 else "agent",
            content=types.Content(
                role="user" if i % 2 == 0 else "model",
                parts=[types.Part(text=f"event #{i}")],
            ),
        )
        await svc.append_event(session=session, event=ev)

    got = await svc.get_session(
        app_name=app,
        user_id=user,
        session_id=sid,
        config=GetSessionConfig(num_recent_events=0),
    )

    print("num_recent_events=0 -> events len =", len(got.events))

asyncio.run(main())

Expected Behavior:

num_recent_events=0 -> events len = 0

This matches the behavior of InMemorySessionService for the equivalent call.

Observed Behavior:

num_recent_events=0 -> events len = 5

All 5 events are returned.

Testing across multiple num_recent_events values suggests that 0 is the only problematic case:

num_recent_events= None -> events len = 5   # OK (no filter)
num_recent_events=    0 -> events len = 5   # Incorrect behavior (should be 0)
num_recent_events=    2 -> events len = 2   # OK
num_recent_events=    5 -> events len = 5   # OK

The issue is reproducible regardless of the underlying database, because the affected branch is in Python (the LIMIT clause is simply never appended to the SQLAlchemy statement).

SQLite is used here only for convenience; PostgreSQL, MySQL, and MariaDB appear to be affected in the same way.

Environment Details:

ADK Library Version (pip show google-adk): 1.33.0
Desktop OS: Linux (WSL2, Ubuntu)
Python Version (python -V): Python 3.12.3

Model Information:

Are you using LiteLLM: No
Which model is being used: gemini-3.1-flash-lite)

Thanks for taking a look.

fix(sessions): respect num_recent_events=0 in DatabaseSessionService

@tiino

@tiino the falsy check on num_recent_events at line 523 is exactly the problem, and swapping it to is not None paired with an explicit == 0 early return (the same pattern SqliteSessionService already uses) is the right fix.

Since you've already got PR #5731 open, could you verify it covers both parts of that change and run your repro script across num_recent_events=0, 2, and None to confirm the behavior holds end-to-end?
Thorough testing across those three cases would really help move the PR forward for review!

@surajksharma07

Thanks for the review, @surajksharma07!

Pushed a follow-up commit (edce3f54) that adds the early return you suggested. The structure now mirrors SqliteSessionService.get_session directly:

if config and config.num_recent_events is not None:
    stmt = stmt.limit(config.num_recent_events)

if config and config.num_recent_events == 0:
    storage_events = []
else:
    result = await sql_session.execute(stmt)
    storage_events = result.scalars().all()

The LIMIT 0 path alone would already return zero rows on any major SQL backend, but skipping the execute() call entirely avoids an unnecessary round-trip — same reasoning as SqliteSessionService (skips execute_fetchall) and VertexAiSessionService (skips the events.list API call). That matters more in this service's typical remote-DB deployments (PostgreSQL / MySQL).

On testing, I extended test_get_session_with_config to cover num_recent_events=2. The parametrized test now runs None, 0, 2, and 3 against all four session backends (InMemorySessionService, InMemorySessionService with light-copy, DatabaseSessionService, SqliteSessionService).

I also ran the end-to-end repro across the three values you called out, using SQLite in-memory backing the DatabaseSessionService:

import asyncio
from google.adk.events.event import Event
from google.adk.sessions.base_session_service import GetSessionConfig
from google.adk.sessions.database_session_service import DatabaseSessionService
from google.genai import types

async def main():
    svc = DatabaseSessionService(db_url="sqlite+aiosqlite:///:memory:")
    app, user, sid = "app", "user_1", "session_1"
    session = await svc.create_session(app_name=app, user_id=user, session_id=sid)
    for i in range(5):
        await svc.append_event(
            session=session,
            event=Event(
                invocation_id=f"inv_{i}",
                author="user" if i % 2 == 0 else "agent",
                content=types.Content(
                    role="user" if i % 2 == 0 else "model",
                    parts=[types.Part(text=f"event #{i}")],
                ),
            ),
        )
    for value in [None, 0, 2]:
        cfg = None if value is None else GetSessionConfig(num_recent_events=value)
        got = await svc.get_session(app_name=app, user_id=user, session_id=sid, config=cfg)
        print(f"num_recent_events={value!r:>5} -> events len = {len(got.events)}")

asyncio.run(main())

Output on current main (before fix):

num_recent_events= None -> events len = 5
num_recent_events=    0 -> events len = 5   # BUG
num_recent_events=    2 -> events len = 2

Output on this branch (after fix + early return):

num_recent_events= None -> events len = 5
num_recent_events=    0 -> events len = 0
num_recent_events=    2 -> events len = 2

@tiino

Thanks for the thorough follow-up @tiino — the two-block structure (is not None for the LIMIT + == 0 early return to skip execute()) is exactly right and mirrors SqliteSessionService line-for-line.

The reasoning around avoiding the unnecessary DB round-trip is especially valid for the typical remote PostgreSQL/MySQL deployment scenario.

One thing worth noting: there are now two PRs open for the same issue (#5731 yours and #5736 from @mangod12), so it's worth taking a quick look at the other to see if the approaches differ meaningfully — maintainers will likely need to pick one or ask for a consolidation.

The parametrized test coverage across all four backends (None, 0, 2, 3) is exactly what reviewers will want to see, and the before/after repro output makes the fix straightforward to validate end-to-end.

Team is looking more into it.

Fixed on main in commit d9a672e (via #5965, also #5731): get_session now uses an is-not-None check, so num_recent_events=0 returns zero events instead of the full history. Thanks for the report and the fix. Closing as landed.

Navigation Menu

Repository navigation

`DatabaseSessionService.get_session` returns all events when `num_recent_events=0` #5730

🔴 Required Information

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

DatabaseSessionService.get_session returns all events when num_recent_events=0 #5730

Description

🔴 Required Information

Activity

surajksharma07 commented on May 18, 2026

tiino commented on May 19, 2026

surajksharma07 commented on May 25, 2026

GWeale commented on Jun 17, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

`DatabaseSessionService.get_session` returns all events when `num_recent_events=0` #5730