[justicezyx]

I dont remember the size, is it 128bits?

It was chosen for future expansion. Kinesis was envisioned to be a much larger-scale Kafka + Storm (storm was the streaming programming framework popular in 2012, it was since falls out of favor).

[ryanworl]

128bit might be accurate, I meant more along the lines of they are non-contiguous and don't seem to be correlated with the amount of records actually being written to a stream.

[crgwbr]

I always assumed they were sequential per-region rather than per-stream, but that’s just a guess.

[justicezyx]

I recall it was sequential per-shard, but no ordering among the shards of the same stream. But I literally haven't touch Kinesis after 2013.