Which Google indexing system announced in 2010 was named for a stimulant?

Google Caffeine was the indexing system named for a stimulant.

Caffeine was Google’s major under-the-hood search infrastructure redesign. Google opened it for developer testing in August 2009 and announced that the new indexing system was fully live on June 8, 2010. Its purpose was to let Google crawl, index, and refresh web content more continuously instead of relying as heavily on large, periodic batches.

Google said Caffeine produced results that were about 50% fresher. The architecture also supported a much larger index and faster processing as the web expanded. Behind the scenes, Google shifted important indexing work away from its earlier MapReduce-based approach toward systems including Bigtable and incremental processing technologies.

The question’s date can cause confusion: Caffeine was announced for testing in 2009, but its completed rollout was announced in 2010. Caffeine was an indexing and infrastructure change, not primarily a visual redesign or a spam penalty. Google Panda and Penguin were later algorithm updates aimed at content quality and webspam, respectively.