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Google·Software Engineer·Onsite - System Design / Architecture·Senior

Senior
May 2026

Summary

Google system design round for a software engineer role. The question was a classic resource-management problem dressed up as log storage, and the O(1) deletion constraint is what made it actually interesting.

Questions Asked (1)

Q1

Design a log management system that enforces a maximum log count, automatically evicts the least important or oldest logs when capacity is exceeded, and can locate the log to delete in O(1) time.

System DesignAlgorithms & Data StructuresTechnical Trade-offs
Author's notes

The capacity enforcement part felt straightforward at first but the O(1) deletion requirement is where it gets tricky.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a data structure that supports O(1) deletion and eviction, such as a combination of a hash map and a doubly linked list. Discuss trade-offs between eviction policies (e.g., oldest vs. least important) and how to handle concurrency and persistence.

Pro tip: Demonstrate awareness of real-world log management systems by mentioning that importance can be modeled as a priority score, and that a heap or multiple lists can handle priority-based eviction while maintaining O(1) deletion via a hash map.

1. Clarify Requirements

Ask questions to understand scale, log importance criteria, eviction policy (oldest vs. least important), and performance needs (O(1) deletion, insertion, eviction).

2. Propose Data Structures

Suggest a hash map for O(1) access to log entries and a doubly linked list for maintaining order or priority, enabling O(1) deletion and eviction.

3. Design Eviction Policy

Explain how to evict the least important or oldest logs: use a min-heap or multiple linked lists based on priority, and update structures on insertion/deletion.

4. Address Concurrency and Persistence

Discuss thread-safety (e.g., locks, concurrent data structures) and durability (e.g., write-ahead logging, periodic snapshots) for a production system.

5. Analyze Trade-offs

Compare approaches: e.g., strict LRU vs. priority-based eviction, memory overhead, and complexity of maintaining multiple indexes.

Key Points to Mention

  • Use a hash map for O(1) lookup and deletion by log ID.
  • Use a doubly linked list to maintain order (for oldest) or multiple lists for priority levels.
  • For least important eviction, assign importance scores and use a min-heap or bucket lists.
  • Ensure O(1) eviction by keeping a pointer to the least important/oldest log.
  • Consider concurrency with read-write locks or lock-free data structures.
  • Discuss persistence and recovery mechanisms for logs.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.