B2B Platform: Legacy ETL to Modern Cloud Warehouse in 8 Weeks

The Challenge

A venture-funded B2B platform had outgrown their legacy data infrastructure. Their analytics ran on a combination of Informatica mappings, stored procedures in SQL Server, and a Looker instance connected directly to their production database.

The problems were compounding:

• Production database load. Analyst queries against the production database were causing latency spikes for end users during business hours. The engineering team had started throttling analytics access
• Informatica maintenance burden. Their two-person data team spent roughly 40% of their time maintaining Informatica jobs — debugging GUI-based transformations, managing scheduling conflicts, and troubleshooting connector issues
• Vendor lock-in. Informatica licensing costs were $85K/year and climbing. The team couldn’t justify the expense for what was increasingly a maintenance burden rather than a productivity tool
• No version control. Transformation logic lived in GUI tools with no audit trail. When a business rule changed, there was no history of what it was before, who changed it, or why

The CEO wanted the data team to support a new product analytics initiative, but they had no capacity — their entire bandwidth was consumed by keeping the existing infrastructure running.

What We Found

Business logic was scattered and undocumented. Critical revenue calculations lived across three Informatica mappings, two stored procedures, and a Looker derived table. Nobody could explain the full chain from source to report without opening five different tools.

The production database dependency was a ticking time bomb. One poorly-written analyst query had caused a 12-minute outage three months prior. The engineering team’s response was to restrict access further — which meant the data team couldn’t do their jobs.

The Informatica-to-Looker pipeline had silent data quality issues. A join condition in one mapping was producing duplicate records for ~3% of transactions. The error was systematic and had been inflating revenue reports for an unknown period.

What We Built

1. BigQuery data warehouse on GCP — fully separated from the production database, with Fivetran connectors for the application database, Stripe, HubSpot, and Intercom
2. dbt transformation layer — all business logic migrated from Informatica mappings and stored procedures into version-controlled, tested SQL models
3. Parallel validation pipeline — ran legacy and modern pipelines side-by-side for three weeks, comparing outputs daily to catch discrepancies and validate accuracy
4. Automated data quality tests — 140+ tests across the dbt project catching issues like the 3% duplicate that had been silently inflating revenue numbers
5. Updated Looker models — reconnected Looker to BigQuery with improved LookML that reflected the clean, documented dbt models

The Result

Migration completed in 8 weeks — from kickoff to the legacy system sunset date. The parallel validation period confirmed that the new pipeline was not only equivalent but more accurate than the old one.

Eliminated $85K/year in Informatica licensing. BigQuery on-demand costs and Fivetran connectors came in at roughly $18K/year — a 79% cost reduction.

Production database fully decoupled. Zero analyst queries against production since week four. The engineering team removed all analytics-related database restrictions.

Fixed the 3% revenue inflation. The duplicate record issue was identified during migration testing and corrected in the dbt model. Finance retroactively adjusted two quarters of reporting.

The team now owns the stack independently. Both data team members were trained on dbt, BigQuery, and the new pipeline architecture. They’ve since added three new data sources and built four new marts without any outside help.