Art of Codeartofcode
Lesson 15 of 16

10. Unique ID Generation

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The picture to keep in your head
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10.1 What makes a good ID?
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10.2 What's wrong with auto-increment?
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10.3 Why does auto-increment break across many servers?
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10.4 What are UUIDs, and which version should you use?
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10.5 How do Snowflake IDs work?
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10.6 What are ticket servers and ID ranges?
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10.7 Why does clock skew matter for time-based IDs?
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10.8 How do you make short IDs with base62?
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10.9 Should IDs be guessable or unguessable?
11
Memory card and where the analogy breaks
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Practice: five levels
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Interview questions
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Solutions
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Sources
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Code lab
10. Unique ID Generation

Sources

3 min read+10 XP

Source notes

  • UUID versions 4 and 7, bit layouts: RFC 9562, "Universally Unique IDentifiers (UUIDs)", May 2024 (replaces RFC 4122). Python's standard library added uuid.uuid7() in Python 3.14 (Python documentation).
  • Snowflake: Twitter Engineering, "Announcing Snowflake", June 2010, and the original open-source project (twitter-archive/snowflake on GitHub): 41-bit timestamp, 10-bit machine ID, 12-bit sequence; refuses to generate when the clock moves backwards.
  • Ticket servers with step and offset: Flickr Code blog, "Ticket Servers: Distributed Unique Primary Keys on the Cheap", February 2010.
  • Instagram's ID scheme (41 bits time, 13 bits shard, 10 bits sequence, generated in PostgreSQL): Instagram Engineering, "Sharding & IDs at Instagram", 2012.
  • Insecure direct object reference (IDOR): OWASP guidance on broken access control.
  • Birthday-bound collision figures for UUID v4 and all other arithmetic: computed 2026-10-08.
  • Level 3 and Level 4 code: tested 2026-10-08 (code/ch10_ids.py, all checks pass).