? All comics

The Schema Migration

DEX TALKS #2 ? Written by Raguvind ? Illustrated with AI

The Schema Migration ? four-panel comic; transcript below.

Open full-resolution image to zoom into the artwork.

Nobody breaks prod on purpose. That's the scary part.

Text version

Panel 1 ? Tuesday, 11:00 AM

PR #842 proposes renaming customer_id to user_id. The author: ?just aligning with the new naming convention, quick cleanup.?

Panel 2 ? The query (broken)

The downstream model still references the old name:

SELECT
  date,
  SUM(amount) AS revenue
FROM fact_payments
WHERE customer_id IS NOT NULL
  AND status = 'success'
  AND event_date = CURRENT_DATE - 1
GROUP BY 1;

Query result: ?Query failed. Column customer_id does not exist.?

The engineer: ?The dashboard still loads. Ship it.?

Panel 3 ? Thursday, 9:18 AM

Monitoring Bot: ?Revenue refresh failed. Showing last successful data.?

Ops: ?Is the dashboard broken?? Finance: ?Did payments go down?? Analytics: ?Anyone looking into this??

The engineer: ?OH NO.?

Panel 4 ? The postmortem

Incident RCA ? Revenue Dashboard Outage. Root cause: customer_id. Fix: user_id.

Lessons: improve cross-team communication, coordinate schema changes, document naming conventions, align on change management, ?? (and 7 more things).?

?One word. Two days. Forty Slack messages.?

Closing

DEX: ?Names change. Consequences don?t.?

?The modern data stack is held together by one-word changes and good intentions.?

?Rename in dev and apologies in prod.?