Cutaway — interactive explainers of systems internals

Interactive explainers of backend and systems internals — WALs, Raft, connection pooling, workflow engines — with the casing removed. Built for engineers who have been paged at 3 AM.

• cutaway/05 · 2026-06-11 · 13 min

  LSM trees: write fast now, pay later

  Your B-tree ingest tops out at 5k rows/s and the SSD is bored — random writes are the bottleneck, not bandwidth. An LSM tree fixes the write path by making reads do the work later. Pile up uncompacted files and watch read amplification climb into the danger zone.

• cutaway/03 · 2026-06-11 · 12 min

  What PgBouncer actually does to your connections

  A Postgres backend is a whole process, so a few hundred of them is a real ceiling. A pooler multiplexes thousands of clients onto a handful of server connections — and the mode you pick decides which of your queries silently break.

• cutaway/02 · 2026-06-11 · 11 min

  Raft leader election, but you control the network

  A primary on the wrong side of a partition is still taking writes. The fix is not a faster failover detector — it is a rule about who is allowed to win. Cut the links yourself and watch Raft refuse to elect two leaders.

• cutaway/04 · 2026-06-11 · 13 min

  How durable workflow engines replay history

  A worker is OOM-killed 40 minutes into an order workflow. It restarts and the order finishes as if nothing happened — nobody wrote recovery code. The trick is replaying recorded history through deterministic code. Crash the worker yourself and watch the local variables refill.

• cutaway/01 · 2026-06-11 · 11 min

  How a write-ahead log survives a crash

  COMMIT returned OK, then the box lost power. Whether that row is still there comes down to one fsync. Kill the database mid-write and watch recovery replay the log.