B0.3 · dive 3 of 3
The stack and the floor.
The shape of what the course builds: the volatile runtime tiers above — echo_data, echo_mq, echo_store — over the durable floor that makes state survive.
The idea
the stack · the floorThe course builds a stack, and the stack has a shape worth seeing before the chapters fill it in. At the top are your systems, written against BCS. Beneath them, echo_data provides the branded id, the property stores, and the CHAMP forest. Beneath that, echo_mq is the Valkey-native bus that moves work between systems. Then echo_store is the declared near-cache, holding hot state close to the systems that read it.
Those tiers are fast because they are volatile, and a system of record cannot be only volatile. The durable floor — Echo Persistence — sits beneath them: an ETS head, the Valkey bus and its L2, a durable local page tier on CubDB or Fjall, and a remote tier on Tigris. State lives somewhere fast and is made durable beneath, on a dial the system sets.
The line between the volatile tiers and the durable floor is the one the persistence chapter draws with care. Part I says state lives somewhere; Part II shows where in the heap; the floor chapter says where it lives when the heap is gone. Reading the stack top to bottom is reading the course in order.
The doors
the sibling coursesEchoMQ — the protocol, in depth
The bus B3 narrates, taught rung by rung: the keyspace, the Lua inventory, and the 3.0 Stream Tier — XADD, XREADGROUP, XACK — with conformance on Valkey.
Redis Patterns Applied
The substrate patterns under the bus: sorted sets, atomic Lua moves, locks, and streams — the judgement layer.
/echo-persistenceEcho Persistence — the durable floor
Beneath the volatile tiers: the Graft page engine built twice, the commit-LSN loop, and the stream archive on Tigris. Where Part I says state lives somewhere, this says where it lives durably.
References
sources · relatedSources
- lucaong — CubDBthe durable local page tier in the floor
- Tigris — Object conditionalsthe create-only fence on the remote tier
- Valkey — Streamsthe Valkey-native bus echo_mq is built on
Related
- BCS — the course homethe law, the id anatomy, the chapter map
- Echo Persistencethe durable floor beneath the bus