Bueno, los “billions” ingleses se corresponden con nuestros millardos, que de todas maneras sigue siendo una cifra tremenda
En el artículo de Computer World al que enlazan está lo interesante:

One of Hasan’s first moves was to buy a Seattle database start-up called Mahat Technologies, which had tweaked the open-source PostgreSQL to run as a column-based database rather than a conventional row-based one. Rotating tables 90 degrees, while slowing down the process of writing data to disk, greatly accelerates the reading of it.
Yahoo brought the database in-house and continued to enhance it, including tighter data compression, more parallel data processing and more optimized queries. The top layer remains PostgreSQL, however, so that Yahoo can use the many off-the-shelf tools available for it.