Every oilfield telemetry project starts the same way. A handful of wells, a few hundred tags, a database that answers in milliseconds. Then the deployment expands to the whole field and the architecture that worked for the pilot stops working entirely. McKinsey found that as many as 74% of manufacturers never got past this stage, and the pattern in upstream oil and gas looks the same. The reason is usually not a bad query. It is that nobody drew the boundary. Every database has a range of conditions inside which it performs to spec, and outside which it fails. That boundary is the performance envelope, and it is defined by three things: how much storage you can afford, how fast you can ingest, and how slow your queries are allowed to get. This session walks through how to calculate that envelope for a real well-monitoring workload before you commit to an architecture. We will do the math on a 10,000 tag deployment at 1 Hz, look at what a year of retention actually costs on cloud SSD, and show where the ingest wall sits. Then we will look at what happens to that envelope when you add TimescaleDB to Postgres rather than replacing it.