Redis 8.12-rc1 folds a side project called redis-roaring into core. It gives bitmaps a second, opt-in internal representation based on Roaring Bitmaps, and a new command, BITRANGEINTARRAY , that reads the set-bit positions straight out of it. The release notes describe this as lowering memory use and speeding up bitmap operations. I wanted to know what that actually means for a bitmap that looks like something I'd really store, not a synthetic all-ones or all-zeros string.

There's no official Docker image for 8.12-rc1 yet, so I built it from the tagged source inside a throwaway container (the commands are in "Run it yourself" below).…