Today, the service has about 90 million users, in addition to the 72 million users of the eBay-owned PayPal. All totaled, these users make 93 billion database calls a day. When the auction site goes down, it costs eBay about US$2,000 a second. There are about 250 million items being auctioned actively on the site at any given time, and the company is gunning for a worldwide rate of a billion items.

The key to increasing efficiency is rethinking your metrics of success, he said.

"Our metrics have changed. It's not just about transactions per second. It comes down to transaction per watt as well as dollar per watt," he said. "All the new platforms that came up were measured to those metrics."

With this metric in place, eBay has applied various techniques to reduce cost on a per-watt basis. It delved into virtualization and moved non-mission-critical applications, such as search, off the "Tier 4" data centers. These centers offer the highest level of availability, but also cost two to four times as much to operate as standard data centers.

It also has pursued an aggressive upgrade cycle, in order to take advantage of the gains of Moore's Law. Nelson said the company now uses Intel's Nehalem processors, noting that the chips, on a per-watt basis, would provide up to five times the performance of previous Intel server processors.