Meridian PostgreSQL/PostGIS Adapter

meridian-storage-postgresql is the Meridian V1 adapter for PostgreSQL and PostGIS. It implements the released Core Adapter SPI and Query translation contract while keeping SQL, topology, credentials, connection pools, and PostgreSQL-specific settings behind the adapter boundary.

The V1 package provides:

• relational, JSON document, authoritative key/value, and evidence-table storage using one physical table per logical Resource;
• tenant and scope injection into every read, write, primary key, and applicable index;
• conditional mutations, atomic claims with FOR UPDATE SKIP LOCKED, and one PostgreSQL READ COMMITTED transaction per Meridian transaction;
• joins, aggregates, signed live-keyset pagination, and WGS84 distance filters evaluated by PostGIS geography in meters;
• bounded recursive relation traversal over the Registry-resolved Relation Collection set—never database metadata or a universal edge table;
• deterministic migration plans, advisory locking, logical export/import, authenticated health probes, and read-only physical-fingerprint checks;
• local single-primary and primary-plus-two-standby conformance profiles.

Installation

python -m pip install meridian-storage-postgresql

Core discovers the adapter through the meridian_storage.adapters entry-point group under the stable id postgresql. Application code continues to use mapping-first Expressions and serialized Operations; it does not import the adapter, psycopg, or SQL builders.

Structured put modes (2.0.0)

The released Structured Catalog defaults to mode="if_absent": an existing scoped identity raises ConflictError. Use mode="update" for an existing record or explicit mode="upsert" to create or update. New PostgreSQL rows start at recordVersion == 1.

structured = meridian.catalog("structured")
created = meridian.execute(structured.put(resource=resource, data=data)).data
updated = meridian.execute(structured.put(
    resource=resource, data=changed_data, mode="update",
    expected_version=created["recordVersion"],
)).data
meridian.execute(structured.put(resource=resource, data=data, mode="upsert"))

A non-null expected version is invalid with if_absent, including zero. For update/upsert, a supplied version requires an existing matching row; zero never creates. Every path retains tenant and configured scope isolation.

This is a breaking change from implicit upsert. Migrate intentional updates and upserts explicitly, refresh the Binding capability fingerprint, and use the compatible package pins below. The adapter rejects old put Operations, missing normalized modes, unsupported versions, and query plans in put input. Other Operation versions and the Adapter SPI are unchanged.

Existing field semantics remain: unconditional updates/upserts assign all mutable non-identity fields, including NULL for omitted nullable fields; version-checked puts update the supplied mutable fields. Immutable-only unconditional puts preserve their existing values and version. Return shape, initial version, update increments, and conflict codes remain unchanged. Core's existing bounded in-process idempotency recognizes same-key replay and returns the original result; a distinct equal-data create conflicts. This release adds no replay store or restart-durable replay guarantee for put.

Binding settings

Platform/Vangu IaC renders meridian.postgresql.settings.v1 into a Meridian Binding. A condensed example is shown below; fingerprints must be canonical sha256: values and real deployments pin every declared Resource.

{
  "formatVersion": "meridian.postgresql.settings.v1",
  "scopeKeys": ["workspace"],
  "topology": {"expectedStandbys": 0},
  "resources": [
    {
      "ref": "structured:example.people",
      "table": "people",
      "profile": "relational",
      "schemaFingerprint": "sha256:<64 lowercase hex characters>",
      "resourceFingerprint": "sha256:<64 lowercase hex characters>",
      "fields": [
        {
          "name": "id",
          "column": "id",
          "logicalType": "uuid",
          "cardinality": "one",
          "nullable": false,
          "mutable": false
        }
      ],
      "identity": ["id"],
      "indexes": [],
      "relation": null
    }
  ]
}

The default profile is postgresql-postgis-local-single-primary with zero standbys. The cluster profile is postgresql-postgis-cluster and requires at least two streaming standbys. The adapter validates those properties; it does not provision, promote, fail over, back up, or restore instances.

Migrations and recovery boundary

Startup opens the pool and performs authenticated/read-only verification only. It never acquires a migration lock and never executes DDL. Platform migration jobs explicitly invoke SchemaCompiler and MigrationExecutor; the executor uses a transaction-scoped advisory lock, compares the expected physical fingerprint, and records a distinct deterministic plan fingerprint before applying DDL. V1 supports initial creation and compatible additive nullable columns. Destructive or otherwise incompatible evolution fails closed for a new design and migration job rather than being inferred by the adapter.

LogicalTransfer provides bounded logical JSON-lines export/import. Physical backup status, backup creation, restore, promotion, identities, ACLs, and lifecycle remain Platform IaC authority. RecoveryHook describes that handoff and intentionally has no administrative side effects.

The package also exposes a released SemanticsAdapter facade for schema validation, activation planning/apply, Registry revision access, canonical encoding/decoding, and logical transfer. It does not add public engine concepts or bypass the Core SPI.

Durable projection outbox (2.1.0)

Deployment composition can inject PostgreSQLOutbox into the released ProjectionRunner. It implements the four owner-based OutboxPort methods without changing the Core Adapter SPI, Writer, or Runner signatures. Business code continues to call TransactionalOutboxWriter through Meridian.

# Deployment/host composition; create_context is the existing AdapterCreateContext
# resolved by the platform from a pinned Binding and secret references.
from meridian_storage.adapters.postgresql import PostgreSQLAdapterFactory, PostgreSQLOutbox
from meridian_storage.projection import ProjectionRunner

adapter = PostgreSQLAdapterFactory().create(create_context)
adapter.open()
try:
    adapter.probe()  # read-only schema, capability and privilege checks
    outbox = PostgreSQLOutbox(
        adapter,
        resource="platform.outbox",
        spec=spec,                 # the same released ProjectionSpec as the runner
        context=worker_context,    # OperationContext: tenant and exact Binding scopes
        poison_threshold=5,
        max_batch_size=1000,
    )
    runner = ProjectionRunner(
        meridian=meridian, spec=spec, project=project,
        outbox=outbox, batch_size=100, lease_seconds=60,
    )
    with meridian.context(worker_context):
        runner.run_until_stopped(stop_event)
finally:
    adapter.close()

The host owns startup, termination, credentials, authorization, retries and scheduling. No SQL or driver client is supplied to application projectors. The injected adapter runtime must contain both the source and outbox Resource mappings; target writes use the runner's Meridian facade and may resolve to a different Binding. Source and intent commit through the Writer's single source Binding transaction. Cross-Binding atomicity is not claimed.

The outbox Resource is a Structured relational Resource with identity eventId. Its immutable Schema and Binding layout contain every OutboxDataV1.to_mapping() field, each with mutable=false and scalar cardinality:

JSON identity/version columns preserve integer, string and null distinctions. The layout uses safe adapter-owned physical column names (for example lowercase logical names). payload and immutableReference are mutually exclusive per the released intent contract. Use only the released Writer to append required intent; insert-only duplicate conflicts leave both original intent and durable progress unchanged. Layout fields cannot be mutable.

An explicit SchemaCompiler / MigrationExecutor deployment migration creates __meridian_outbox_state and __meridian_outbox_checkpoint when an outbox layout is configured. Apply the new plan and refresh the physical fingerprint before startup. Existing databases with no outbox layout keep their previous DDL. Runtime probes and provider construction only read and validate the metadata shape, unique keys and privileges; they never create or repair tables. Grant the runtime SELECT/INSERT/UPDATE on these metadata tables through IaC. Declare scope-leading source/identity/version and occurrence/event indexes on large outbox Resources through the normal Schema and Binding index configuration.

State and checkpoint keys include tenant, all configured scopes, outbox Resource and projection name. Changing filters for the same projection retains its leases and checkpoints. A different projection name consumes independently. Claims filter the exact source Catalog, Resource, Schema and required target labels. Only the earliest incomplete version for each source identity is eligible. Numeric versions order numerically; opaque versions use occurrence and event-id order. Independent identities may run concurrently. Quarantine blocks later work for that identity and is never skipped automatically.

Claims lock a bounded batch with FOR UPDATE SKIP LOCKED and persist owner, acquisition, expiry and attempt before returning. Concurrent activity can produce a short batch; subsequent calls retain the remaining work. Expired claims become eligible for reclaim. Release persists retry/quarantine with a redacted failure category; exception messages and payloads are not stored. Completion checks exact source version and current non-expired ownership, then advances the checkpoint by CAS and marks completion in one transaction. Expiry during checkpoint persistence rolls back both effects. Database time is used unless the caller explicitly supplies the port's deterministic UTC now parameter.

The existing owner-only protocol does not fence claim generations. Hosts must avoid overlapping reuse of an owner string. A target acknowledgement may be replayed after a host crash; the projector/target must implement idempotent, version-aware writes. get(event_id) and checkpoint(partition_key) are adapter-owned deployment diagnostics, not new OutboxPort requirements.

Development

uv sync --extra test
uv run ruff check .
uv run mypy
uv run pytest
uv build
uv run twine check dist/*

Genuine integration tests cover postgis/postgis:16-3.4-alpine and postgis/postgis:17-3.5-alpine; they are skipped unless MERIDIAN_POSTGRESQL_TEST_DSN is set. See docs/conformance.md for exact commands and evidence.

Compatibility

Version 2.1.0 pins Core 1.0.1, Semantics 2.0.0, Query 1.0.2, and Projection 1.0.2. The Adapter SPI remains 1.0.0; structured.put uses Operation contract 2.0.0. The locked design revisions and supported PostgreSQL/PostGIS profiles are recorded in the wheel's compatibility.json. Native PostgreSQL queries are intentionally excluded from V1.

License

Apache License 2.0. See LICENSE and NOTICE.