The application was silently rewriting created_at after record creation, making child records appear older than their parents. Here is how I caught it and fixed it using raw CDC history in the dbt staging layer.
I built a paper trading bot that runs on a Raspberry Pi 5, executes 8 strategies across stocks and crypto, and has been trading a simulated 10,000 euro portfolio since early 2026. This post covers the technical details: the strategy code, the backtester that validated the strategies against 195,000 candles, the yfinance pitfalls that cost me days of debugging, and the web dashboard that lets me monitor everything from my phone.
I spent two days hunting a revenue bug that produced numbers exactly 100 euros off on specific records. The SQL was correct. The data model was correct. The individual fields were correct. The bug was in how I was combining them — a subtle interaction between revision-aware bid fields and delta-based quote adjustment fields in a Unified Star Schema metrics bridge.
Our data team of four was drowning in ad-hoc requests. “What was the revenue last month?” “How many active customers do we have in Germany?” “What’s the conversion rate for Q4?” Each question meant someone opening a SQL editor, writing a query, formatting the results, and posting them in Slack. So I built an AI-powered data assistant: a Slack bot backed by Claude and BigQuery that lets anyone on the team ask business questions in natural language and get SQL-backed answers in seconds.
How two duplicate webhook events, arriving 2ms apart, broke 12 dbt tests in production — and the surprisingly simple fix that made the sync idempotent.
We had been paying roughly 400 euros a month for a managed ETL connector to sync our CRM data into BigQuery. Six tables, a few thousand records each, updated a handful of times per day. The connector worked, but it had problems: data landed in a US-region dataset (we needed EU for GDPR compliance), the CDC implementation had quirks that caused phantom duplicates, and every time we needed to debug something we were staring at a black box. So I replaced it with a custom Cloud Run service. The whole thing runs for under 5 euros a month.
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