Docs›Guides›Table›Foreign Table›Foreign Table Delta

DeltaLake Foreign Table

Learn how to integrate Delta Lake with Tacnode using foreign tables, enabling seamless access to Databricks Unity Catalog and Delta format data lakes.

Delta Lake is an open-source table format that brings ACID transactions, data versioning, and performance optimizations to data lakes. This guide covers integrating Delta Lake tables with Tacnode through Databricks Unity Catalog and direct Delta format access.

Delta Lake Overview

Delta Lake provides enterprise-grade reliability and performance for data lakes:

Key Features

Feature	Benefit	Use Case
ACID Transactions	Data consistency and reliability	Concurrent writes, data quality
Time Travel	Data versioning and recovery	Audit trails, rollback operations
Schema Evolution	Backward compatibility	Adding columns, changing types
DML Operations	UPDATE, DELETE, MERGE support	Data maintenance, CDC
Optimization	Automatic file management	Query performance, cost efficiency

Unity Catalog Integration

Install Delta FDW Extension

The following instructions are written to be run from the psql command line

-- Install Delta Lake foreign data wrapper
CREATE EXTENSION IF NOT EXISTS delta_fdw;

-- Verify installation
SELECT extname, extversion 
FROM pg_extension 
WHERE extname = 'delta_fdw';

-- Check available FDW options
\des+ delta_fdw

Create Unity Catalog Foreign Server

-- Production Unity Catalog server
CREATE SERVER unity_production FOREIGN DATA WRAPPER delta_fdw
OPTIONS (
    unity_catalog_endpoint 'https://dbc-12345678-9abc.cloud.databricks.com',
    aws_region 'us-west-2',
    catalog 'production_catalog'
);

-- Analytics catalog server
CREATE SERVER unity_analytics FOREIGN DATA WRAPPER delta_fdw
OPTIONS (
    unity_catalog_endpoint 'https://dbc-87654321-def0.cloud.databricks.com',
    aws_region 'us-east-1',
    catalog 'analytics_catalog',
);

Configure Authentication

Authentication

CREATE USER MAPPING FOR current_user SERVER unity_production
OPTIONS (
    unity_catalog_token 'dapi1234567890abcdef1234567890abcdef12',
    -- Storage credentials
    aws_access_id 'AKIA...service-account-key',
    aws_access_key 'service-account-secret'
);

Import Schema and Tables

Import Entire Schema

-- Import all tables from a Unity Catalog schema
IMPORT FOREIGN SCHEMA "sales_data"
FROM SERVER unity_production
INTO public;

-- Import specific tables only
IMPORT FOREIGN SCHEMA "customer_analytics"
    LIMIT TO (customer_segments, purchase_history, churn_predictions)
FROM SERVER unity_analytics
INTO analytics_schema;

-- Import all except certain tables
IMPORT FOREIGN SCHEMA "raw_data"
    EXCEPT (temp_table, test_data)
FROM SERVER unity_production
INTO raw_schema;

Best Practices

Use Unity Catalog for centralized metadata management and governance
Enable predicate pushdown to minimize data transfer and improve performance
Implement proper authentication with service principals for production environments
Monitor schema evolution and plan for backward compatibility
Leverage time travel for data recovery and auditing scenarios
Create materialized views for frequently accessed Delta data
Implement row-level security for multi-tenant scenarios
Regular quality checks to ensure data integrity across versions

Limitations

Write operations through foreign tables are not supported
Some Delta Lake features may require direct Spark access
Large table scans can be expensive - use appropriate filtering
Schema changes in Unity Catalog may require foreign table recreation
Time travel queries increase storage costs - monitor usage

This comprehensive approach to Delta Lake integration enables you to leverage enterprise-grade data lake capabilities while maintaining the flexibility and performance of Tacnode’s query engine.