Fix AttributeError In Events Compaction With DatabaseSession

Experiencing the dreaded AttributeError during events compaction with DatabaseSessionService can be a real headache. This article breaks down the issue, offering a comprehensive look at the root cause, reproduction steps, and potential solutions. We'll explore the intricacies of the bug, its impact, and how to address it effectively.

Understanding the Problem

The core of the issue lies in the serialization and deserialization of compaction event objects. When using EventsCompactionConfig alongside DatabaseSessionService, particularly with SQLite, the application might intermittently crash with the infamous AttributeError: 'dict' object has no attribute 'start_timestamp' within the _process_compaction_events() function. This error arises because the compaction event objects, initially stored as objects with accessible attributes, are being retrieved from the database as simple dictionaries. The code, however, expects these objects to retain their original attribute structure, leading to the crash.

Key Takeaway: The AttributeError occurs due to a mismatch between the expected object type (with attributes) and the actual object type (dictionary) after deserialization from the database.

Reproducing the Error

To truly grasp the problem, let's walk through the steps to reproduce it. This will give you a hands-on understanding and allow you to verify the fix once implemented.

1. Environment Setup: Ensure you have the necessary environment configured, including google-adk, google-genai, Python, and a SQLite database.
2. Enable Events Compaction: Configure your application with EventsCompactionConfig enabled. This is the trigger for the compaction process that eventually leads to the error.
3. Use DatabaseSessionService: Utilize DatabaseSessionService with a SQLite backend. This is where the serialization and deserialization discrepancies come into play.
4. Run Multiple Conversation Turns: Execute several conversation turns within your application. This will generate enough data to trigger the compaction process based on the defined compaction_interval.
5. Observe the Crash: The error typically manifests on subsequent runs after compaction data has been stored in the database from a previous execution.

Code Snippet:

import os
import asyncio
from google.adk.agents import LlmAgent
from google.adk.apps.app import App, EventsCompactionConfig
from google.adk.models.google_llm import Gemini
from google.adk.sessions import DatabaseSessionService
from google.adk.runners import Runner
from google.genai import types

# Configure API key
os.environ["GOOGLE_API_KEY"] = "blahblahblah"
os.environ["GOOGLE_GENAI_USE_VERTEXAI"] = "FALSE"

# Create agent with compaction
agent = LlmAgent(
    model=Gemini(model="gemini-2.5-flash-lite"),
    name="test_agent",
    description="Day 2 Section 3 compaction bug"
)

# Create app with compaction enabled
app = App(
    name="compaction_bug_test",
    root_agent=agent,
    events_compaction_config=EventsCompactionConfig(
        compaction_interval=3,
        overlap_size=1,
    ),
)

# Use database session service (this is where the bug manifests)
session_service = DatabaseSessionService(db_url="sqlite:///test_compaction.db")
runner = Runner(app=app, session_service=session_service)

async def test():
    session = await session_service.create_session(
        app_name="compaction_bug_test",
        user_id="test_user",
        session_id="test_session"
    )

    # First run works just fine, but...
    for i in range(4):
        query = types.Content(role="user", parts=[types.Part(text=f"Message {i+1}")])
        async for event in runner.run_async(
            user_id="test_user",
            session_id=session.id,
            new_message=query
        ):
            pass

    print("Survived first run - run again to trigger the bug")

asyncio.run(test())

Running this code snippet, especially on the second execution, should trigger the AttributeError if the environment is correctly set up.

Analyzing the Root Cause

Delving deeper into the code, the issue resides in the _process_compaction_events() function within /google/adk/flows/llm_flows/contents.py. Specifically, line 265 attempts to access compaction.start_timestamp under the assumption that compaction is an object with attributes. However, after retrieval from the DatabaseSessionService, compaction is a dictionary, hence the AttributeError. This points to a crucial serialization/deserialization problem within the session storage layer.

Code Snippet (Faulty Line):

compaction.start_timestamp is not None  # Line 265

The root cause boils down to the fact that the code expects an object with attribute access, but it receives a dictionary. This highlights the need for consistent object handling throughout the compaction process, especially when persistence is involved.

Potential Solutions

Now that we understand the problem and its cause, let's explore potential solutions to rectify this AttributeError and ensure smooth operation of events compaction with DatabaseSessionService.

1. Dictionary Access: Modify the code to use dictionary access methods instead of attribute access. This involves replacing compaction.start_timestamp with compaction.get('start_timestamp') or compaction['start_timestamp']. This approach adapts the code to work with the dictionary format.

   compaction.get('start_timestamp') is not None
   

   or

   compaction['start_timestamp'] is not None
   

2. Proper Deserialization: Ensure that compaction events are properly deserialized into the expected object type after retrieval from the database. This might involve custom deserialization logic or adjusting the session storage layer to maintain object integrity.

   This approach would require modifying how DatabaseSessionService retrieves and deserializes the data, ensuring it's converted back into the original object structure before being passed to _process_compaction_events().

3. Hybrid Approach: Combine both dictionary access and proper deserialization to create a robust solution. Use dictionary access as a fallback mechanism in case deserialization fails, ensuring the code doesn't crash even if the object isn't fully restored.

   timestamp = getattr(compaction, 'start_timestamp', compaction.get('start_timestamp'))
   if timestamp is not None:
       # ...
   

Recommendation: The best approach would likely be a combination of both. Proper deserialization ensures the code works as originally intended, while dictionary access provides a safety net for unexpected scenarios.

Impact of the Bug

The consequences of this bug can be significant, especially in production environments. The primary impact is the complete disruption of the persistence feature when using events compaction. This can lead to:

• Loss of Session Data: The application might fail to maintain session state correctly, leading to a poor user experience.
• Unpredictable Behavior: The application's behavior can become unpredictable due to the inability to properly compact and manage events.
• Increased Error Rates: The AttributeError can flood logs and monitoring systems, making it harder to identify other issues.

Critical Consideration: This bug affects any production use case that relies on persistent sessions with compaction. It's essential to address it promptly to avoid potential data loss and application instability.

Additional Context and Considerations

• Predictable Nature: The error is predictable as it only occurs when compaction data already exists in the database from a previous run.
• Serialization Mismatch: The root cause points to a serialization/deserialization mismatch in the session storage layer.
• Fresh Runs: Fresh database runs work fine on the first execution, highlighting the persistence aspect of the issue.

Debugging Tip: When debugging, focus on the data flow between the database and the _process_compaction_events() function. Inspect the type of the compaction variable at line 265 to confirm whether it's an object or a dictionary.

Requested Fix and Resolution

To effectively resolve this issue, it's crucial to ensure that compaction event objects are properly serialized and deserialized when using DatabaseSessionService. This maintains attribute access compatibility and prevents the AttributeError. Alternatively, update all access patterns to handle dictionary objects consistently.

Proposed Steps:

1. Implement Deserialization: Modify DatabaseSessionService to ensure that compaction events are deserialized into objects with attribute access.
2. Add Dictionary Access: As a fallback, use dictionary access methods in _process_compaction_events() to handle cases where deserialization might fail.
3. Thorough Testing: Conduct extensive testing to verify that the fix resolves the issue and doesn't introduce any new problems.

Conclusion

The AttributeError in events compaction with DatabaseSessionService is a nuanced issue stemming from serialization and deserialization inconsistencies. By understanding the problem, reproducing the error, analyzing the root cause, and implementing appropriate solutions, you can effectively address this bug and ensure the stability and reliability of your application. Remember to prioritize proper deserialization while providing a fallback mechanism for unexpected scenarios.

For more information on the google-adk library and its components, refer to the official google-adk documentation.