Clock skew

Machine clocks drift apart by milliseconds or more, so timestamps from different servers cannot be trusted to order events. Last-write-wins based on wall clocks silently loses data.

Where it shows up in real systems

  • Unique ID generator

    Snowflake-style IDs pack a timestamp, a machine number and a sequence into 64 bits, so every server can generate them independently. UUIDv7 offers the same ordering in 128 bits.

    In production: Twitter Snowflake, UUIDv7, ULID, Sonyflake

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