Crate eventsdb_core 

An embedded, append-only event log.

eventsdb is an event store that lives in the process rather than behind a socket. It keeps the guarantees an event store exists for — immutable facts, per-stream ordering, decisions taken inside the write, schema evolution without rewriting stored bytes — and drops the ones that require a cluster.

The layers

Layer	What it answers
event	what a valid event is, and which fields the store owns
upcast	how a reader sees an old event’s current shape
store	one stream: append, decide-and-append, read, head
log	the database: read across streams, subscribe, checkpoint

This crate is the contract and the in-memory backend. A durable backend is a separate crate implementing the same two traits.

What single-writer buys

Two properties this design has are not available to a store that runs as a separate service, and both come from the same place — one writer, one transaction:

• Positions have no holes. The backend allocates a position::Position inside the transaction that commits it, so a reader never sees n + 1 while n is still uncommitted. Following the log is a range read, with no gap detection and no grace window.
• A projection can be exactly-once. When the read model lives in the same database as the log, applying an event and advancing the consumer’s checkpoint are one transaction. There is no dedupe table and no idempotence requirement on the projection author.

Distributing the store forfeits both.

Re-exports

pub use error::Error;

pub use error::Result;

pub use event::validate;

pub use event::CURRENT_SCHEMA_VERSION;

pub use log::EventLog;

pub use log::Filter;

pub use mem::MemEventStore;

pub use position::Committed;

pub use position::Position;

pub use position::Recorded;

pub use store::Decision;

pub use store::EventStore;

pub use store::Expected;

pub use transfer::ExportedEvent;

pub use transfer::ImportReport;

pub use upcast::Current;

pub use upcast::UpcastChain;

pub use upcast::Upcaster;

Modules

error

The error a store call can fail with.

event

The event envelope: what a caller may write, and what the store stamps.

log

The database-level SPI: one level above a stream.

mem

The in-memory backend.

position

Coordinates: where an event sits in its stream, and in the database.

store

The per-stream SPI.

transfer

Moving a log somewhere else, and getting the same log back.

upcast

Schema evolution: stored bytes are never rewritten, readers are moved forward instead.