Crate rhei_oltp_rusqlite 

Rusqlite-backed OLTP engine for the Rhei HTAP database.

Position in the HTAP pipeline

rhei-oltp-rusqlite is the transactional layer of Rhei. It sits between application clients and a local SQLite database file, and acts as a CDC source for the rhei-sync crate’s CdcSyncEngine, which replicates mutations into the OLAP backend (DuckDB or DataFusion).

Client SQL
   │
   ▼
RusqliteEngine  (implements rhei_core::OltpEngine)
   ├── write connection  ─ all INSERT / UPDATE / DELETE / DDL
   ├── read pool (N connections, round-robin) ─ SELECT
   └── CDC connection  ─ polls _rhei_cdc_log
          │
          ▼
       RusqliteCdcProducer  (implements rhei_core::CdcConsumer)
          │
          ▼
       CdcSyncEngine  ──▶  OlapBackend

Threading model

rusqlite::Connection is not Send, so every connection is pinned to its own dedicated OS thread (via rhei_tokio_rusqlite). Async callers dispatch closures through a crossbeam_channel and receive results on a tokio::sync::oneshot channel — no unsafe code required.

RusqliteEngine opens connections with the following SQLite pragmas:

• journal_mode=WAL — readers never block the writer.
• synchronous=NORMAL — durable on most workloads without full fsync.
• busy_timeout=5000 — retry for up to 5 s when the database is locked.

Trigger-based CDC

When cdc_setup::setup_cdc is called for a table, three SQLite triggers are installed (AFTER INSERT, AFTER UPDATE, AFTER DELETE). Each trigger appends one row to the _rhei_cdc_log table.

Row data is serialised as a json_array() expression rather than json_object() because the array form skips key serialisation, yielding roughly a 10 % reduction in trigger write overhead. RusqliteCdcProducer reconstructs the keyed JSON object at poll time by fetching the column order from PRAGMA table_info — this also handles schema evolution correctly, since column names are never stored in the log itself.

Key public types

Type	Role
RusqliteEngine	OLTP engine: write connection + read pool
RusqliteCdcProducer	CDC consumer: polls _rhei_cdc_log
RusqliteOltpError	Unified error type for this crate

Re-exports

pub use cdc_producer::RusqliteCdcProducer;

pub use engine::RusqliteEngine;

pub use error::RusqliteOltpError;

Modules

cdc_producer

CDC event consumer backed by the _rhei_cdc_log SQLite table.

cdc_setup

CDC trigger installation and teardown for SQLite tables.

engine

RusqliteEngine: the async SQLite OLTP engine.

error

Error types for the rhei-oltp-rusqlite crate.