Implement a sliding window log for API analytics
Last updated: August 6, 2025
Quick Overview
Build a data structure that efficiently tracks API request counts and latencies over sliding time windows (last 1 minute, 5 minutes, 1 hour). Support high-throughput concurrent writes and low-latency reads.
Affirm
August 6, 202512
9
4,523 solved
Build a data structure that efficiently tracks API request counts and latencies over sliding time windows (last 1 minute, 5 minutes, 1 hour). Support high-throughput concurrent writes and low-latency reads.
API observability is critical at Affirm for monitoring payment system health. This problem tests your ability to design efficient data structures for real-time analytics, a common need in high-throughput financial systems.
What the Interviewer Expects
- Choose an appropriate data structure for time-windowed aggregation
- Implement efficient insertion and query operations
- Handle concurrent access safely
- Optimize memory usage by pruning old entries
- Support multiple aggregation windows without duplicating data
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you add percentile latency calculations (p50, p95, p99)?
- How would you aggregate across multiple server instances?
- What is the memory upper bound of your solution?
- How would you support custom time ranges for ad-hoc queries?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem at hand requires tracking API request counts and latencies efficiently over multiple sliding time windows: 1 minute, 5 minutes, and 1 hour. This is a classic use case for a **sliding windo...
Approach
To implement the sliding window log, we will use a data structure that maintains a queue for each time window (1 minute, 5 minutes, 1 hour) to track the timestamps and latencies of API requests. The a...
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