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LeadTechInterview
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| # Lead Tech Interview :link: https://leadtechinterview.github.io | ||
| ### :page_facing_up: [16](https://leadtechinterview.github.io/tag.html) | ||
| ### :page_facing_up: [17](https://leadtechinterview.github.io/tag.html) | ||
| ### :speech_balloon: 0 | ||
| ### :hibiscus: 70422 | ||
| ### :alarm_clock: 2025-01-16 04:39:39 | ||
| ### :hibiscus: 73305 | ||
| ### :alarm_clock: 2025-01-16 09:02:37 | ||
| ### Powered by :heart: [Gmeek](https://github.com/Meekdai/Gmeek) |
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| # Requirements (5 mins): | ||
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| ## Functional Requirements | ||
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| > Identify core features (e.g., "Users should be able to post tweets"). Prioritize 2-3 key features. | ||
| 1. users can start/stop/pause their activity (runs/rides) | ||
| 2. users should be able to check the activity data (route, distance, time etc) when running /riding | ||
| 3. users should be able to check history records, including friends | ||
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| ## Non-Functional Requirements | ||
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| > Focus on system qualities like scalability, latency, and availability, consistency, security, durability, fault tolerance. Quantify where possible (e.g., "render feeds in under 200ms"). | ||
| 1. the system should be highly available | ||
| 2. the app should work offline when no Internet | ||
| 3. the stats should be accurate | ||
| 4. should support 10m concurrent users | ||
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| ## Capacity Estimation | ||
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| > Skip unnecessary calculations unless they directly impact the design (e.g., sharding in a TopK system). | ||
| route GPS data estimation: 100m DAU, 10m concurrent users, collect interval 5 secs, 30 min activity per day will generate 30 x 60 / 5 = 360 records, so around 36,000m records per day, each record we have around 40 Byte. | ||
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| Storage: 36,000m x 40 = 1440GB per day. 1500G x 360 = 180000x3G = 540000 GB = 540 TB | ||
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| QPS 3600m / 100k = 36k | ||
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| ## Core Entities (2 mins) | ||
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| > Identify key entities (e.g., User, Tweet, Follow) to define the system's foundation. | ||
| - user | ||
| - activity | ||
| - route | ||
| - friend | ||
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| # API/System Interface (5 mins) | ||
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| > Define the contract between the system and users. Prefer RESTful APIs unless GraphQL is necessary. | ||
| - POST /activity -> Activity, create an activity, body {type} | ||
| - PATCH /activity/id, change status, body { status}, start, stop, pause, complete | ||
| - POST /activity/id/route, update route geo tracking { geolocation} | ||
| - GET /activities/page?mode=user|friend&page= | ||
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| # [Optional] Data Flow (5 mins) | ||
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| > Describe high-level processes for data-heavy systems (e.g., web crawlers). | ||
| # High-Level Design (10-15 mins) | ||
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| > Draw the system architecture, focusing on core components (e.g., servers, databases). Keep it simple and iterate based on API endpoints. | ||
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| # Deep Dives (10 mins) | ||
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| > Address non-functional requirements, edge cases, and bottlenecks. Proactively improve the design (e.g., scaling, caching, database sharding). | ||
| ## No internet connection | ||
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| We can save data in local db and sync to server later | ||
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| ## Support 100 DAU, 10m concurrent users | ||
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| storage: 540TB/year | ||
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| - purge old storage of route date | ||
| - shard data by time | ||
| - use cold storage to save cost | ||
| - compress the date | ||
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| QPS: 40k | ||
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| - use nosql database, time series database more specific | ||
| - clients aggregate the data and use longer intervals if not in realtime view | ||
| - shard the data by user id, activity id to distribute the load across servers | ||
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