Replace plain dict cache in analytics_service with cachetools TTLCache

Problem

app/services/analytics_service.py uses a plain _cache = {} dict with manual preloading (_preload_medicines(), _preload_doctors()) to avoid N+1 queries. This cache has no TTL, no eviction policy, and no thread safety guarantees — stale data will accumulate for the lifetime of the process.

Location

app/services/analytics_service.py lines ~34–45

Fix

Option A (quick): Replace with cachetools.TTLCache:

from cachetools import TTLCache
_cache = TTLCache(maxsize=128, ttl=300)  # 5-minute TTL

Option B (correct): Remove the manual cache entirely and use SQLAlchemy eager loading (selectinload / joinedload) on the queries that cause N+1.

Option B is preferred long-term. Option A is a safe immediate improvement.

References

• https://cachetools.readthedocs.io/
• https://docs.sqlalchemy.org/en/20/orm/queryguide/relationships.html

Effort

Low–Medium (1–2h)