···171718181919research bitcask
2020+2121+2222+2323+fetch: take current pack, remove dead objects/holes, filter objects
2424+out, record offsets and adjust ofs_deltas since they always go
2525+backwards, write the pack back; then stream written pack to client.
2626+two-step necessary because pack header includes object count; could
2727+have a custom new protocol that doesn't do so.