# An hourly_subscription_metrics pipeline costs $48,000/month Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem An hourly_subscription_metrics pipeline costs $48,000/month. The structured cost-reduction pass brings it to $4,700/month without breaking SLAs. The audit identifies four wins: full table rebuild every hour (fix with incremental + partition overwrite), wrong partition column (predicate filters on event_time but partition is on ingest_time), full pull from Stripe API every hour (fix with delta pull and rate-limit respect), and an over-frequent run cadence (consumer SLA is 2 hours, not 1). Sequence the fixes by adding a cost-pass transform on the canvas whose name states the four levers in execution order and the verification at each step (lineage check, pillar check, cost rollup). ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/an-hourlysubscriptionmetrics-pipeline-costs-48000month-16201f2a) - [System Design Interview Questions](https://datadriven.io/data-engineering-system-design) - [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep) - [Daily Challenge](https://datadriven.io/daily) --- Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.