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Comment by random5634 | Hacker News Reader

How do you use 64 bits and only get scale to 180 years? For that bit count I’d expect 1000+

A Sonyflake ID is composed of

  39 bits for time in units of 10 msec
  8 bits for a sequence number
  16 bits for a machine id

Why do the bits add up to 63 rather than 64?

Presumably to make them work with languages that don't recognize unsigned integers? For example Java...

Just a guess without reading the code, the unused bit is probably to avoid complications from signed integers. If the sign bit is never set, signed and unsigned integers can store the same data.

Does this mean that using them in a multi-threaded context may produce duplicate ids?

Edit: To answer my own question. No, although it does seem to limit your application to a single process with at most 256 threads, if I'm reading it correctly.

> Sequence numbers are per-thread and worker numbers are chosen at startup via zookeeper (though that’s overridable via a config file). [0]

[0] https://blog.twitter.com/engineering/en_us/a/2010/announcing...

This proves my point. 39 bits for time in 10 msec is something like 17x years.

ULID runs through 10889 AD

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