System Design: Searchable Short-Form Status Updates with Nearby Search

Context

Design a microblogging service where users post short text updates (think: "statuses"). Users must be able to search:

• Full-text across historical posts (e.g., keyword search, filters by time/language).
• Geolocation-based "nearby" results (e.g., find posts within a radius from a location, sorted by distance and/or recency).

Assume internet-scale usage with high read and write throughput and global users.

Requirements

1. Functional
   • Users can create, edit, and delete short text posts (e.g., up to 280 characters), optionally with a location (lat, lon).
   • Public search: keyword queries across all public posts; filters for time range, language, and presence of geolocation.
   • Nearby search: given (lat, lon) and radius, return relevant posts near that location, supporting sort by distance and/or recency.
   • Respect privacy/visibility (e.g., public vs restricted); search should only show authorized content.
2. Non-Functional
   • Low latency: p50 < 200 ms, p95 < 500 ms for typical searches; writes < 150 ms.
   • Freshness: new posts searchable within seconds (near real-time indexing).
   • High availability and horizontal scalability; multi-region read latency optimization.
   • Cost-effective historical search (tiered storage for older data).

What to Design

• High-level architecture (write path, index pipeline, search path).
• Data model and storage choices for posts and indexes.
• Full-text indexing and query processing (tokenization, ranking, pagination).
• Geolocation indexing and query execution for nearby search.
• Scaling/sharding strategies, caching, and consistency/freshness trade-offs.
• Handling edits/deletes, privacy filtering, and operational considerations (monitoring, reindexing).