Why Do Ecommerce Backends Keep Overselling Stock?
A focused, ~3 hour course that teaches you the exact schema, tradeoffs, and edge cases most engineers only learn after their system breaks in production.
Join the waitlist/Get early access.
It's 11:47 PM on a Friday during a flash sale. A limited drop sells 40 units. Only 25 exist in stock.
Now support is fielding angry emails. Someone's writing a postmortem. And the fix isn't a quick patch - it's realizing the entire data model was built wrong from day one.
Here's the uncomfortable part: almost every ecommerce backend starts with the same naive model - an orders table, an order_line_items table, and an inventory table with a single quantity column. It works in every demo. It works in every code review. It works right up until two checkouts hit at the same moment, then it silently sells something that doesn't exist.
Most engineers find this out the expensive way: in production, under pressure, with a customer already charged. This course exists so you find out in an afternoon instead - before it costs you a 2 AM page, a bad postmortem, or a promotion conversation that goes sideways because "the inventory system" is the reason revenue got flagged.
If you already know "don't use a single mutable quantity column", good - that's not what this course is about. This is about the five implementation decisions that come after you already know that: row-locking or optimistic concurrency, how reservations expire without leaving zombie holds, how to handle duplicate checkout requests, when a ledger actually needs Redis in front of it, and how to keep an append-only log fast as it grows. That's the part nobody teaches, and it's the part that actually determines whether your system holds up.
You've shipped a few CRUD APIs. You can build an endpoint, model a table, ship a feature. But you've never had to design something that survives two customers checking out the same item at the same time - or you have, and it didn't go well.
- You're being handed more ownership - a system design interview is coming up, or you're the one now expected to make the architecture call instead of just implementing someone else's.
- You just joined (or are about to join) an ecommerce or marketplace company, and you've inherited an inventory system nobody's touched since it started breaking under real traffic - now it's your job to understand it, or fix the parts that don't hold up.
- You are building your own product and there's no senior engineer around to catch the mistake before it ships to real customers with real money on the line.
- You've already been paged for an inventory bug and never got a clean answer for why it happened or how to actually prevent the next one.
Skip this one if: you haven't shipped an API to real users yet - this assumes you can already build the happy path and want the layer above it. And if you just want whiteboard answers to recite in an interview, save your money - this is a hands-on build, not a script to memorize.
What you'll walk away with
Not notes. Not concepts you'll forget by the time you need them. An actual system you built, and the judgement to defend every decision in it.
- A working, production-grade order and inventory schema - built by you, lesson by lesson, not handed to you as a finished file to skim.
- A completed end-to-end flow - add-to-cart -> reservation -> payment -> commit/release -> fulfillment - that goes straight into your portfolio, GitHub, or your next system design interview.
- Real SQL you can paste into your project today, not slides-only theory you'll forget in a week.
- A decision framework for the concurrency tradeoff - row-locking vs. optimistic concurrency vs. Redis-backed hot paths - so you can justify the choice in a design review, not just implement one option blindly.
- The failure modes named and explained before you hit them - overselling, orphaned reservations, refunds that don't reconcile - instead of debugging them at 2 AM with an incident channel open.
Why not just read a free blog post about this?
Fair question. A few reasons this is different:
- This is a built project, not an explainer. You're implementing the schema and flow yourself across 6 lessons, not reading about someone else's implementation.
- It's sequenced. Free content on this topic exists scattered across blog posts, Stack Overflow threads, and engineering blogs - each covering one piece with no connective structure. This puts the entire decision tree in order, in one sitting, so you're not stitching it together yourself from a dozen tabs.
- It's honest about its edges. This course tells you explicitly what it doesn't cover (the distributed/microservices version of the problem) rather than pretending one course solves everything - so you know exactly what you're getting.
- AI can write the code. It can't make the call. Ask an AI assistant to write you a reservation system and it will - competently. What it won't do is walk you through why row-locking beats optimistic concurrency for your specific traffic pattern, or catch you before you make the tradeoff that only becomes a problem three months from now. That judgement is what this teaches.
I've spent 13 years as a backend engineer, most of it building and fixing ecommerce systems. I've watched the story above happen more than once - at more than one company, in more than one stack. It's not a one-off mistake. It's what happens by default when nobody's told you the alternative before you ship. This is the course I wish someone had handed me before I learned it the hard way.
This is the free waitlist - not the course itself. The course isn't live yet, and there's nothing to buy here.
Join now and you'll get an email the moment it's ready - early access before the public launch, a lower price than what it'll eventually sell for, and direct input into what the later lessons cover. If that's you, join below.
You can find this out in production, at 11:47 PM on a Friday. Or you can find it out here, in an afternoon, on your own terms.
What's pulling you toward this?