Hacker News Reader

My understanding is: your proposal is not very different from what Shopify is doing except they are tracking 'reserved units' (one per row) and you are proposing tracking 'orders' as the temporary state to then reconcile back with inventory quantities.

View on HN

Yes, at a high level. It doesn't rely on skip locked, which is not cheap at DB level. DB has to still typically run query and keep going until it finds an unlocked item. Deducting and checking inventory counts are simpler ops inside the DB.

This seems like what triggers are for and how we do similar type things. Update trigger on order does select for update on the inventory and increases/decreases it as appropriate.

I don't think you really need that even. An indexed lookup is fast and you don't need to store a computed quantity generally.

Reply on news.ycombinator.com