feat(memory): SQL-backed DatabaseMemoryService with scratchpad for durable agent memory

[Raman369AI]

Summary

The ADK currently ships only InMemoryMemoryService (volatile, keyword-only, test-only) and cloud-specific Vertex AI services. There is no durable, self-hosted memory option for production deployments that do not use Vertex AI.

Problem

Developers running ADK agents on-premise or against non-Google cloud providers have no way to persist agent memory across process restarts without writing their own implementation from scratch.

Proposed Solution

Add DatabaseMemoryService — a BaseMemoryService implementation backed by any SQLAlchemy-supported async database (SQLite, PostgreSQL, MySQL, MariaDB, Spanner via the existing SQLAlchemy adapter).

Core features

• Durable memory — events and direct MemoryEntry writes are stored in a SQL table (adk_memory_entries) that survives process restarts
• Idempotent session ingest — add_session_to_memory is safe to call multiple times (DELETE + re-INSERT)
• Delta ingest — add_events_to_memory skips already-stored event_ids
• Pluggable search — MemorySearchBackend ABC allows swapping in FTS or vector-embedding backends; ships with KeywordSearchBackend (LIKE/ILIKE, AND-first → OR-fallback)
• Scratchpad — a KV store (adk_scratchpad_kv) and append-only log (adk_scratchpad_log) for intermediate working memory during task execution, exposed as four BaseTool subclasses agents can call directly

Zero-config for SQLite

from google.adk.memory import DatabaseMemoryService

svc = DatabaseMemoryService("sqlite+aiosqlite:///:memory:")  # tests / local dev
svc = DatabaseMemoryService("postgresql+asyncpg://user:pass@host/db")  # production

New public API surface

Symbol	Module
DatabaseMemoryService	google.adk.memory
MemorySearchBackend	google.adk.memory
KeywordSearchBackend	google.adk.memory
scratchpad_get_tool	google.adk.tools.scratchpad_tool
scratchpad_set_tool	google.adk.tools.scratchpad_tool
scratchpad_append_log_tool	google.adk.tools.scratchpad_tool
scratchpad_get_log_tool	google.adk.tools.scratchpad_tool

Test coverage

38 unit tests using sqlite+aiosqlite:///:memory: (no external DB required):

• All BaseMemoryService methods
• Scratchpad KV and log operations
• All 4 tool happy-paths and wrong-service error paths
• Multi-user isolation and session scoping

Files changed

src/google/adk/memory/schemas/__init__.py          (new)
src/google/adk/memory/schemas/memory_schema.py     (new)
src/google/adk/memory/memory_search_backend.py     (new)
src/google/adk/memory/database_memory_service.py   (new)
src/google/adk/tools/scratchpad_tool.py            (new)
src/google/adk/memory/__init__.py                  (modified — adds exports)
tests/unittests/memory/test_database_memory_service.py (new)

Related

Complements the existing DatabaseSessionService which follows the same SQLAlchemy async pattern.