Five weeks, 562 commits: Felix from 0.5.0 to 0.6.0
What we found, fixed and added between Felix 0.5.0 and 0.6.0: the bugs that shared one shape, the ways we found them, the features that apps asked for and why, and what building it taught us.
Fast, without losing messages
How Felix answers a fsynced publish in a third of a millisecond, writes at the disk's full rate under load, and slows publishers down instead of dropping their messages.
Acknowledged, then forgotten: a crash under periodic fsync
Under Felix's default periodic fsync, a crashed broker could come back missing records it had acknowledged while the cluster still counted it as caught up; this is how review and the TLA+ model found it on the follower and leader sides, and what the fix costs.
The follower that forgot
On an idle shard nothing ships, so a leader never learned that a follower had lost its disk; this is how a storage identity per data directory fixed that, and why it changes only when a directory may hold less than its peers were told.
Introducing Felix: one log for streams, caches and counters
What Felix is, how a publish travels from a client to disk to every subscriber, why it is built that way, and how to run it on your laptop in five minutes.