1. A scalable computer system for managing orders and inventory in a store that makes sales at a physical retail location, through an online storefront, and through an online marketplace where third party goods are sold to customers, the scalable computer system comprising: a sharded store order database that is horizontally scalable under an order management system application layer, the sharded store order database comprising: a first order database shard in a first order database server, the first order database shard having inventory data for a first group of orders, the first group of orders corresponding to first items which have been sold by the store at the physical retail location; a second order database shard in a second order database server, the second order database shard having order data for a second group of orders, the second group of orders corresponding to second items which have been sold by the store through the online storefront, the second group of orders being different than the first group of orders; and a third order database shard in a third order database server, the third order database shard having order data for a third group of orders, the third group of orders corresponding to the third party goods which have been sold through the online marketplace, the third group of orders being different than the first group of orders and the third group of orders being different than the second group of orders; a store order management computer system comprising: a computer processor; memory connected to the computer processor; and an order shard determination module programmed to: receive a first query regarding a first order to purchase a first ordered item from the store, wherein the first ordered item is one of the first items; identify a first order database shard associated with the first order; communicate data regarding the first order to the first order database shard; receive a second query regarding a second order to purchase a second ordered item from the store, wherein the second ordered item is one of the second items; identify a second order database shard associated with the second order; communicate data regarding the second order to the second order database shard; receive a third query regarding a third order to purchase a third ordered item, wherein the third ordered item is one of the third party goods; identify a third order database shard associated with the third order; and communicate data regarding the third order to the third order database shard.