## Problem You are given a Python snippet that implements a user session cache. Identify all bugs, performance issues, and design problems. Be prepared to explain the impact of each issue and propose fixes. ```python sessions = {} def get_session(user_id): if user_id not in sessions: sessions[user_id] = {"created": time.time(), "data": load_from_db(user_id)} return sessions[user_id] def invalidate_session(user_id): del sessions[user_id] def cleanup_old_sessions(): for uid, session in sessions.items(): if time.time() - session["created"] > 3600: del sessions[uid] ``` **Your task:** List every issue you can find in 10 minutes. Rewrite the module addressing all concerns. ## Follow-ups 1. `cleanup_old_sessions` modifies a dict while iterating — what error does this cause and how do you fix it? 2. The global dict is not thread-safe. How would you make this safe for a multi-threaded web server? 3. If this service runs across 10 instances, what breaks and how do you fix it? 4. How would you add an LRU eviction policy when memory usage exceeds a threshold?

InterviewDB Experience

Code Review: Identify Bugs, Performance Issues, and Design Flaws in a Given Code Snippet

Onsite

Interview Experience

Problem You are given a Python snippet that implements a user session cache. Identify all bugs, performance issues, and design problems. Be prepared to explain the impact of each issue and propose fixes. Your task: List every issue you can find in 10 minutes. Rewrite the module addressing all concerns. Follow-ups cleanup_old_sessions modifies a dict while iterating — what error does this cause and how do you fix it? The global dict is not thread-safe. How would you make this safe for a multi-thr…

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This is a candidate experience report from a abnormal security interview during the onsite round.

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