We have several disparate systems. These systems assign ORDER numbers. Basically, these are sequential numbers. They are NOT database ID numbers. These order numbers are like "A01457" or "Z4T456", etc. The problem is that each application issues its own order number and obviously order numbers can (and are) duplicated. Business has grown and now management want's the numbers to be unique across all systems because they want to roll orders up to a warehouse server.
The requirement is to develop an autonomous application (web service) that will accept simultaneous requests for an order number. The new application will generate and issue a unique order number to each request. Generating the order number is not the problem.
The problem is how to ensure that the order numbers are issued sequentially during multiple simultaneous requests?
What is the best practice for this type of implementation?
We prefer to use apache + php.