[boyd]

So a bitmap index requires a bit per unique value IIRC (plus the key and some amount of overhead). So for ~32 unique values you're already at 4 bytes, 40 bytes per key-value pair for 320 values, etc.

In comparison, a B-field will let you store 32 distinct values at ~3.4 bytes (27 bits) per key-value pair at a 0.1% FP rate.

[foota]

Yes, I'm not claiming that they're going to perform as well, just that they're sort of similar in the space of problems.

There's different techniques used for compressing them, mostly around sorting the keys and e.g., run length encoding the values.