Size matters: Yahoo claims 2-petabyte database is world's biggest, busiest:
"Take Yahoo Inc.'s 2-petabyte, specially built data warehouse, which it uses to analyze the behavior of its half-billion Web visitors per month. The Sunnyvale, Calif.-based company makes a strong claim that it is not only the world's single-largest database, but also the busiest.
Based on a heavily modified PostgreSQL engine, the year-old database processes 24 billion events a day, according to Waqar Hasan, vice president of engineering in Yahoo's data group.
And the data, all of it constantly accessed and all of it stored in a structured, ready-to-crunch form, is expected to grow into the multiple tens of petabytes by next year."