MSSQL -> Postgres

This guide is a copy/paste-ready starting point for loading data from MSSQL into Postgres with dpone.

Status: Batch ETL supported

Type profile: mssql_to_postgres_native_v1. Vendor-live evidence uses a wide typed fixture (dpone_src → Postgres dpone_it) and covers Docker strategies full_refresh, incremental_append, incremental_merge, replace, partition_replace, snapshot_diff, scd2, and backfill (inner replace) via tests/integration/mssql/test_mssql_to_postgres_vendor_live_integration.py. Extract uses Postgres-safe CSV (Postgres rejects mssql-delimited); binary columns land as bytea via \x hex CSV. See Route live wide certification.

Vendor-live IT (manual)

docker compose -f docker/docker-compose.integration.yml up -d mssql postgres
export DPONE_RUN_INTEGRATION=1 DPONE_RUN_INTEGRATION_LIVE=1
uv run pytest tests/integration/mssql/test_mssql_to_postgres_vendor_live_integration.py -q

When to use this path

Use this path when MSSQL is the system of record or ingestion boundary and Postgres is the landing, warehouse, event-log, or downstream replication target.

Copy/paste manifest

# yaml-language-server: $schema=../../src/dpone/schema/etl-batch-manifest.schema.json
kind: dpone.batch.v1

defaults:
  name: mssql_to_postgres_example
  source:
    type: mssql
    connection_id: mssql_source
    options:
      batch_size: 50000
      export_format: csv
  sink:
    type: postgres
    connection_id: postgres_dwh
    table:
      schema: public
      name: orders
    strategy:
      mode: incremental_merge
      unique_key: order_id
      merge_policy: delete_insert
      duplicate_policy: fail

quality:
  gates:
    - id: source_target_rows
      type: row_count_reconciliation
      severity: error
      tolerance:
        mode: pct
        value: 0.1

schemas:
  dbo:
    tables:
      - orders

Run it locally:

dpone plan examples/source-sink/mssql-to-postgres.yaml --format md
dpone run examples/source-sink/mssql-to-postgres.yaml

The checked source file is examples/source-sink/mssql-to-postgres.yaml; CI compares its parsed YAML with this block.

If you change the strategy to full_refresh and empty output is invalid, row-count reconciliation is not enough: it can pass a 0 source / 0 target comparison. Add an explicit non-empty target gate:

quality:
  gates:
    - id: target_min_rows
      type: min_rows
      side: target
      threshold: 1
      severity: error

Supported load strategies

These rows describe public runtime contracts, not certification of this exact source, sink, transport, schema-evolution mode, and runtime combination.

Strategy	Status	Notes
full_refresh	Supported	Uses staging first, then applies the target-specific finalization plan.
incremental_append	Supported	Uses staging first, then applies the target-specific finalization plan.
incremental_merge	Supported	Default merge_policy: delete_insert; shadow_swap is available for DB targets.
replace	Supported	Uses staging first, then applies the target-specific finalization plan.
partition_replace	Supported	Replaces target partitions represented by staging partition.column; see Load strategies for native/fallback paths.
snapshot_diff	Supported	Requires a complete bounded snapshot and unique_key; applies the configured diff/delete policy.

See Load strategies for the detailed algorithm for each strategy. MSSQL CDC is a source capability, not a load strategy. It uses typed CDC offsets and advances source state only after sink success; certify the exact route and environment before enabling it.

Runtime algorithm

This sink does not currently implement StagedLoadPort, so this route records governance_finalization=legacy_post_finalize. Blocking gates run only after the sink has mutated or finalized the target. A failure prevents source-state advancement but cannot roll back that target mutation; inspect and repair or deduplicate the target before retrying. See Load governance.

flowchart TD
    A["Resolve manifest and registry entries"] --> B["Create MSSQL source"]
    B --> C["Plan bounded extract"]
    C --> D["Read through BCP queryout or pyodbc streaming cursor"]
    D --> E["Emit ExtractResult with schema and artifact"]
    E --> F["Plan schema evolution"]
    F --> G["Create Postgres staging or event batch"]
    G --> H["Load through COPY-compatible staging load followed by set-based finalization"]
    H --> I["Apply finalization strategy"]
    I --> J["Run quality and reconciliation checks (legacy_post_finalize)"]
    J --> K["Advance state only after success"]

Strategy behavior

• full_refresh: extract the selected source boundary, load into staging, and replace the target according to the target's safe finalization path.
• incremental_append: extract only the incremental boundary and append rows through staging or event production.
• incremental_merge: load into staging, validate duplicates, then use delete_insert by default; shadow_swap is available where table swaps are supported.
• replace: reload a bounded predicate window through staging and then atomically replace the matching target slice.
• snapshot_diff: compare a complete current source snapshot with the target by unique_key, then apply the configured insert, update, and delete policy.
• partition_replace: extract a complete partition slice, load it into staging, and replace only partitions represented by partition.column.

Snapshot reconciliation is separate from the load strategy. Runtime planning reports that capability as reconciliation.mode=snapshot; in the official dpone.batch.v1 authoring schema, enable it with reconciliation: true.

Schema evolution and type mapping

Pair profile mssql_to_postgres_native_v1 maps MSSQL metadata types to Postgres DDL before staging/final load (integer/smallint/bigint, numeric(p,s), boolean, timestamp/timestamptz, varchar/text, uuid, bytea, …). Unknown or spatial/sql_variant types require an explicit schema_contract.

Schema evolution is enabled by default and runs before the staging/final load path:

1. Read source schema from ExtractResult.schema (pair-mapped for Postgres).
2. Introspect the Postgres target schema.
3. Apply safe additions and widening operations.
4. Fail breaking changes by default.
5. If configured, route incompatible type changes to __dpone__nc__<column>.

Use Schema evolution and Type mapping matrix when adding columns or changing source types.

Self-service golden path

Copy-paste CJM for the checked-in example (wide vendor-live certified route):

dpone doctor --profile local
pip install "dpone[mssql,postgres]"
dpone plan examples/source-sink/mssql-to-postgres.yaml --format md
dpone schema type-matrix --source mssql --sink postgres --format md
dpone run examples/source-sink/mssql-to-postgres.yaml

Landing convention (vault/GitOps-oriented): examples/batch/landing_mssql_to_postgres.batch.yaml.

See Route live wide certification for the maintainer vendor-live IT evidence path (SKIP ≠ PASS).

Runbook

1. Start with dpone doctor --profile local and fix missing extras or native clients.
2. Run dpone plan examples/source-sink/mssql-to-postgres.yaml --format md and review source boundary, staging path, schema evolution, state, and quality gates.
3. Run a small bounded window first.
4. Inspect the run artifact under .dpone/runs/mssql_to_postgres.
5. For incremental jobs, verify state before enabling a schedule.
6. For delete-aware jobs, run reconciliation in report-only mode before enabling physical deletes.
7. Promote the manifest through GitOps after the plan and artifact are reviewed.

Cross-links

• Source -> sink matrix
• Load strategies
• Schema evolution
• Type mapping matrix
• Reconciliation and CDC
• Performance guide

Type contracts and physical design

This flow supports the shared dpone type-governance stack:

• Type inference for source metadata, sampled profiling, confidence, and empty string vs NULL behavior.
• Schema contracts for explicit logical column types, enforcement modes, and __dpone__nc__* variant columns.
• Physical design for target-specific DDL such as concrete SQL types, indexes, partitioning, compression, ClickHouse LowCardinality, and BigQuery clustering.

Use dpone schema infer --manifest ... and dpone schema physical-plan --manifest ... before enabling new table DDL in production.