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Interview prep for xAI
author June Park <parkjune1995@gmail.com>
date Mon, 15 Dec 2025 19:55:17 -0800
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1 # Distributed Cache (Focus: Hashing & System Logic)
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3 - Question: Implement a Cache Router
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5 Level 1 (Easy - Modulo Hashing): Write a function that maps a key (string) to one of N servers.
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7 Task: Implement getServerIndex(key, serverCount).
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9 Expected Logic: Simple hash modulo: hash(key) % serverCount.
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11 Critique: The interviewer will ask, "What happens to the existing keys if we add one server (change N to N+1)?" (Answer: Almost all keys get remapped, causing a massive cache miss storm).
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13 Level 2 (Medium - Consistent Hashing): Solve the remapping problem. Implement a ConsistentHash class.
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15 Task: Map servers to points on a circle (0 to 360 degrees or a large integer range). Map keys to the same circle. A key belongs to the first server it encounters moving clockwise.
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17 Goal: Prove that adding a server only requires remapping the keys that fall between the new server and its predecessor.
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19 Level 3 (Hard - Virtual Nodes): The servers have uneven capacity, or the data distribution is skewed (some segments of the ring have way more keys).
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21 Task: Modify the class so that each physical server exists at multiple points on the ring (e.g., "Server A" is at positions 10, 150, and 290).
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23 Goal: Distribute load more evenly and handle "hot spots" better.
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25 ---
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27 Questions:
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29 - Async
30 - Threads
31 - DB
32 - Cache
33 - KV
34 - Distribution
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37 ---
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39 FE
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41 - Fetching URL
42 - Storing it as useMemo and what not.
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