Because then you run into an issue when you 'n' changes. Plus, where are you increasing it on? This will require a single fault-tolerant ticker (some do that btw).
Once you encode shard number into ID, you got:
- instantly* know which shard to query
- each shard has its own ticker
* programatically, maybe visually as well depending on implementation
I had IDs that encode: entity type (IIRC 4 bit?), timestamp, shard, sequence per shard. We even had a admin page wher you can paste ID and it will decode it.
id % n is fine for cache because you can just throw whole thing away and repopulate or when 'n' never changes, but it usually does.
