Module redb 

redb-backed kv backend (M4.D — DS-14-storage Audit 4, ACID transactions).

RedbBackend wraps a redb::Database as a StorageBackend. Each write() / delete() opens its own write transaction and commits — ACID guarantees per call. read() / list() use read transactions (concurrent with any write). flush() is a no-op (writes are durable on commit). Space reclamation is managed internally by redb; flush() is a no-op since each write() commits its own transaction.

All keys live in a single "graphrefly" table (D162 — tiers already namespace via key prefixes; a single table matches the flat-kv model of [MemoryBackend] / [FileBackend]).

Thread safety

redb::Database is Send + Sync. begin_write() serializes concurrent writers by design (MVCC — one writer at a time, concurrent readers). No additional synchronization needed on RedbBackend. This structurally closes the F3 deferred concern (concurrent flush race on append-log) — see porting-deferred.md.

Crash safety

redb is crash-safe by default — committed transactions survive process crashes. Unlike [FileBackend]’s per-file atomic-rename, redb provides cross-key atomicity within a single transaction. The per-write-call transaction granularity (D163) means each StorageBackend::write() is individually atomic; cross-key atomicity (e.g., flushing multiple append-log buckets) would require holding one transaction across multiple calls, which isn’t supported by the current StorageBackend trait. Cross-key atomicity at the tier level is a M4.E concern (Graph::attach_storage batched flush).

Cargo feature: gated behind redb-store (default-on).

Structs

RedbBackend

redb-backed StorageBackend.

Functions

redb_append_log

Append-log tier over a redb backend at path.

redb_append_log_default

Append-log tier over a redb backend with default options (JsonCodec).

redb_backend

Open or create a redb database at path, returning an Arc<RedbBackend>.

redb_kv

KV tier over a redb backend at path.

redb_kv_default

KV tier over a redb backend with default options (JsonCodec).

redb_snapshot

Snapshot tier over a redb backend at path.

redb_snapshot_default

Snapshot tier over a redb backend with default options (JsonCodec).