# booblik

> A broker that fits in one head and one process: topics into partitions, partitions into segments, offsets the consumer keeps. No ZooKeeper, no quorum.

Page: https://kotlin.website/booblik

## Why it exists

The niche is not "a Kafka replacement". It is a broker that fits in one head and one process —
no ZooKeeper, no KRaft quorum, no group coordinator. Everything that makes Kafka operable as a
cluster is deliberately absent; everything that makes a log fast is reproduced and **measured**.

## What you get

- **Segments** with a sparse offset index, two write paths (`FileChannel` and an FFM memory
  mapping), rolling, retention by size and age, and recovery from a torn write.
- **A per-partition writer actor with no timer.** It groups whatever is already in its mailbox
  into one barrier, so the batch size *is* the load, measured at the instant before the write.
  No configured window means no latency floor to retune.
- **Zero-copy FETCH** straight from the page cache to the socket with `transferTo`.
- **Long FETCH** — a caught-up consumer waits on the broker instead of polling, and a write
  during the wait wakes it immediately.
- A client library: pipelined connections matched by correlation id, an accumulating producer,
  key-based routing, and subscriptions as `Flow<RecordBatch>`.

## What is deliberately missing

**TLS and compression.** Both require transforming the bytes, and transforming them means
copying them — they are incompatible with the zero-copy path by construction, not merely
unimplemented. Per-record CRC32C is verified on every read that touches the bytes, which the
zero-copy path by definition does not; saying so is more useful than a footnote claiming
end-to-end verification.

Runtime topic creation is out for the same kind of reason: the partition set is fixed at
startup, and that is what removes the coordinator.

## Measured, not asserted

Numbers come from a rented Linux machine with nothing else running and, for end-to-end
figures, two such machines with a 7.85 Gbit/s link — the broker in its own process, the load
generator on the other host. Methodology and full tables are in `docs/benchmarking.md`.