How to Build an Inventory Management Solution That Prevents Stock Drift

Description and use

The solution prevents stock drift by ensuring atomic, idempotent, and auditable inventory changes, reducing overselling and improving replenishment accuracy.

Problem

Warehouse dashboards often show more available stock than the picking team can find, leading to overselling, failed fulfilment, and incorrect replenishment decisions.

Outcome

The solution prevents stock drift by ensuring all inventory changes are atomic, idempotent, and auditable, reducing overselling and improving replenishment accuracy.

Workflow

• Define separate tables for inventory_balance, inventory_reservation, inventory_movement, and processed_events.
• Use a composite key on (sku, warehouse_id) to avoid duplicate balance records.
• Implement a conditional UPDATE on inventory_balance that reserves stock only if sufficient unreserved quantity exists.
• Wrap the UPDATE, reservation creation, and movement recording in a single database transaction.
• Insert a record into processed_events with a unique constraint to deduplicate events.
• If the event is a duplicate, rollback and return a duplicate flag.
• If the conditional UPDATE fails, throw an error for insufficient stock.
• Commit the transaction on success.
• Separate external notifications from database commits to avoid race conditions.
• Retry failed downstream notifications via a background worker.

Evidence

A warehouse dashboard can show 120 units available while the picking team finds only 93.

Source

The following PostgreSQL statement performs a conditional reservation.

Source