get_session() event retrieval lacks pagination support

[ferponse]

Description

When calling get_session(), all events for a session are loaded into memory at once. While GetSessionConfig offers num_recent_events and after_timestamp for basic filtering, there is no proper pagination mechanism (offset/token-based) to retrieve events in manageable chunks.

For sessions with thousands of events (e.g. long-running agent conversations), this causes high memory usage and slow response times when fetching a session.

Impact

• Memory pressure: Loading 5k+ events into a single Session object is expensive, especially when the caller only needs a subset.
• Latency: In our deployment with PostgreSQL, get_session() for a session with ~3k events takes ~8 seconds due to deserializing all event data at once.
• No random access: There's no way to fetch events starting from a specific position (e.g. "give me events 100-120") without loading everything up to that point.

Current behavior

config = GetSessionConfig(num_recent_events=50)
session = await session_service.get_session(
    app_name="app", user_id="user", session_id="sid", config=config
)
# Gets last 50 events, but no way to get the *next* 50 before those

num_recent_events acts as a simple LIMIT from the tail — there's no continuation mechanism.

Proposed solution

Add an EventPagination class (similar to SessionPagination from #4873) to GetSessionConfig:

from google.adk.sessions.base_session_service import EventPagination

config = GetSessionConfig(
    event_pagination=EventPagination(page_size=50)
)
session = await session_service.get_session(
    app_name="app", user_id="user", session_id="sid", config=config
)

# Access paginated events
events = session.events  # up to 50 events
next_token = session.next_event_page_token  # token for next page

This would allow efficient retrieval of event history in chunks, which is essential for building features like scrollable conversation history in UIs.

Related

• list_sessions() performance degrades significantly with large session counts #4871 — pagination for list_sessions() (same pattern)
• DatabaseSessionService.list_sessions lacks pagination support #4621 — original report on list_sessions() performance

Environment

• google-adk version: 1.27.2
• Python: 3.11
• Database: PostgreSQL (async via asyncpg)

[sasha-gitg]

closing in favor of: #4621