An updated version of Google's paper about MapReduce (available at ACM and mirrored here) provides new information about Google's scale. MapReduce is a software framework used by Google to "support parallel computations over large (...) data sets on unreliable clusters of computers". Google uses it for indexing the web and computing PageRank, for processing geographic information in Google Maps, clustering news articles, machine translation, Google Trends etc.The input data for some of the MapReduce jobs run in September 2007 was 403,152 TB (terabytes), the average number of machines allocated for a MapReduce job was 394, while the average completion time was 6 minutes and a half. The paper mentions that Google's indexing system processes more than 20 TB of raw data. Since 2003, when MapReduce was built, the indexing system progressed from 8 MapReduce operations to a much bigger number today.
Niall Kennedy calculates that the average MapReduce job runs across a $1 million hardware infrastructure, assuming that Google still uses the same cluster configurations from 2004: two 2 GHz Intel Xeon processors with Hyper-Threading enabled, 4 GB of memory, two 160 GB IDE hard drives and a gigabit Ethernet link.
Greg Linden notices that Google's infrastructure is an important competitive advantage. "Anyone at Google can process terabytes of data. And they can get their results back in about 10 minutes, so they can iterate on it and try something else if they didn't get what they wanted the first time."
| Aug. '04 | Mar. '06 | Sep. '07 | |
| Number of jobs (1000s) | 29 | 171 | 2,217 |
| Avg. completion time (secs) | 634 | 874 | 395 |
| Machine years used | 217 | 2,002 | 11,081 |
| map input data (TB) | 3,288 | 52,254 | 403,152 |
| map output data (TB) | 758 | 6,743 | 34,774 |
| reduce output data (TB) | 193 | 2,970 | 14,018 |
| Avg. machines per job | 157 | 268 | 394 |
| Unique implementations | |||
| map | 395 | 1958 | 4083 |
| reduce | 269 | 1208 | 2418 |
{ The screenshot illustrates a Google rack from 2007. I don't remember the exact source of the image, but it's likely to be a presentation. }