Federation Engines

A source type says where data lives. A federation engine is the runtime Provisa compiles that data's queries into — the thing that holds the connectors, executes the plan, and owns the materialization store. The two are separate registries: SourceType in provisa/core/models.py lists what you can register, _ENGINE_BUILDERS in provisa/federation/engine.py lists what can run it. trino and several warehouses appear in both, meaning Provisa can read a Trino cluster as a source, run on one as an engine, or do both at once against different clusters.

Provisa ships 32 engine keys. [tool-verified: provisa/federation/engine.py _ENGINE_BUILDERS]

Federating engines

These reach sources in place through connectors, so a cross-source JOIN can run without landing every input first.

Key	Engine	Notes
trino	Trino (embedded MPP)	Provisa-managed Trino cluster; JVM heap and cluster config are editable in Admin and regenerate on restart
trino-byo	Trino (bring your own)	External coordinator — same runtime, connection only, no cluster tuning
pg	PostgreSQL	BYO or embedded; federates via FDWs or pg_duckdb
duckdb	DuckDB (in-process)	Native partial federator; the desktop and demo default
clickhouse	ClickHouse (embedded chdb)	OLAP federator (REQ-909); the only engine with a Hudi path (REQ-1178)
clickhouse-server	ClickHouse (server or cloud)	Same runtime as above, URL-driven

Warehouse engines

Partial federators: the warehouse executes, and sources it cannot reach natively land into it first. Each reads Arrow-natively where the vendor's client supports it.

Key	Engine	Notes
snowflake	Snowflake	Self-only MPP warehouse, Arrow-native (REQ-988)
databricks	Databricks	Partial federator, Arrow-native (REQ-987)
bigquery	BigQuery	Partial federator; GCS external links
fabric	Microsoft Fabric Warehouse	T-SQL; OneLake OPENROWSET links
synapse	Azure Synapse serverless SQL	T-SQL; ADLS OPENROWSET links

SQLAlchemy engines

One runtime with zero federation connectors: every source LANDs into the target store and is then federated with plain SQL. sqlalchemy takes any URL from $PROVISA_ENGINE_URL; the 20 keys below are the same runtime pre-named per database so a picker can name the product rather than the library (REQ-905, REQ-1421). [tool-verified: provisa/federation/engine.py _RDB_KINDS, build_sqlalchemy_engine]

Key	Engine
sqlalchemy	Any SQLAlchemy URL
mysql, mariadb, tidb, singlestore	MySQL and its wire-compatible relatives
greenplum, cockroachdb, yugabytedb, opengauss	PostgreSQL-wire relatives
oracle, mssql, db2, teradata	Enterprise RDBMS
saphana, sapase, sqlanywhere	SAP
redshift, vertica, exasol, monetdb	Analytic stores
firebird	Firebird

File-embedded stores are absent on purpose: the engine's store must be reachable over the network from wherever Provisa runs, which a local file on someone else's disk is not.

Two narrower lists

The 32 keys are the complete set, but two other places name a subset on purpose, and they are not the same list:

• The install wizard offers 5 options — duckdb, pg_duckdb, postgres_fdw, trino, sqlalchemy. These are provisioning choices, not builder keys: pg_duckdb and postgres_fdw are two ways to provision the one pg engine. A wizard option must declare its platforms, provisioning route and startup cost, and the demo preset may only use bundled instant ones. [tool-verified: config/capabilities.yaml roles.federation_engine.options]
• The Admin engine picker renders the selectable-engine registry, which pairs each key with the config fields that engine needs. A selection persists to the platform config and binds on the next service restart, because the engine is chosen once at boot (REQ-916). [tool-verified: provisa/federation/engine.py, the registry following _ENGINE_BUILDERS]

What an engine changes

Engine choice decides which sources are reachable in place versus landed as a replica. Ask the running system rather than inferring it: reachable_source_types(engine_key) returns what an engine can federate, and live_source_types(engine_key) returns the subset it queries without materializing. [tool-verified: provisa/federation/engine.py:1215, :1234]