I found the comparison with 'Real Businesses' particularly funny, given Wal-mart have have 2.1 million employees worldwide and Twitter has 75 million users...their scaling requirements are different by a factor of 35.
I'm pretty sure that Walmart's databases track way more interesting things than tweets.
I'd assume that they know where every pallet of product is located anywhere in the world and what's in it, where every truck is and what's in it, the referrer for every click on their web site, details on every purchase at every store, location of every incoming product from every supplier.....
And then I'd assume that they take all that data and de-normalize it, move it to a whole different series of databases, poke it into star schemas and warehouse it for further analysis - 'cause y'know - red wieners might be more popular than blue wieners next xmas, and they'd better anticipate that by at least 6 months, 'cause the wiener factories have to re-tool.
Listen to rm-rf. Way back when (2003-2004), I was involved in Walmart's supply chain managament software. I recall a few million rows to be optimized every day (before noon, so the hundreds of trucks plying the road can move things around efficiently).
You're comparing two completely different businesses on disparate metrics.
How many 'users' does WalMart have worldwide? I'd say at least 500 million on whom they keep a purchase record. Then there's products, credit card numbers, suppliers, etc.
But in terms of their 'real business' it is not the number of customers they have but the number of they have but only their employees who will be using their systems. The purchase records, products and credit card numbers are closer to Tweets than users.
I don't think the number of people doing data entry or accessing a system matters nearly as much as how much data one has to be tracked. WalMart's data needs exceed that of Twitter, they exceed the needs of Facebook. I don't know if they meet or exceed Google, but I'd imagine it's up there.
