Design a prioritized log manager with eviction

Q: Design a prioritized log manager with eviction

This question evaluates system design and algorithmic competencies in bounded storage management, specifically prioritized eviction, recency-aware ordering, per-file and global capacity accounting, and choosing data structures that meet stated complexity targets.

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This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at Google.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Google during technical interviews.

Question

Design a Log Store with Priority- and Recency-Aware Eviction

Context

You are designing an in-memory (or on-disk) log storage component. Each inserted log belongs to a file (fileId) and has a priority and a timestamp. Storage is bounded by a global capacity and optional per-file capacities. When capacity is exceeded, the system must automatically evict the "least important" logs first. Importance is defined by priority (higher = more important) and recency (newer = more important).

Requirements

Global capacity: The total number of stored log records across all files must not exceed total_max .
Automatic eviction: addLog(fileId, record, priority, timestamp) must automatically evict when limits are exceeded.
Eviction policy: When eviction is required, delete the least important records first. Importance considers:
- Priority (higher is more important), and
- Recency (newer is more important).
Limits: Support both per-file limits (optional limit[fileId] = X ) and a global limit total_max .
APIs and complexity targets:
- Provide APIs to add logs, query by file, and observe capacities.
- Target complexities: O(1) (or amortized O(1)) to identify a deletion candidate and O(log n) or better per insertion/eviction.

Deliverable

Describe your data model, data structures, eviction policy, algorithms, and trade-offs that meet the above requirements and complexities.

Design a prioritized log manager with eviction

Quick Overview

Design a Log Store with Priority- and Recency-Aware Eviction

Context

Requirements

Deliverable

Solution

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