I think we should not take "rewrite" too literally. But both, search and adwords, have been rewritten multiple times since their launch. You can have a look a

I think we should not take "rewrite" too literally. But both, search and adwords, have been rewritten multiple times since their launch. You can have a look at the papers created by Jeff Dean (1) and Sanjay Ghemawat (2) which mention some of the new concepts/technologies/features used in those products. 1: https://ai.google/research/people/jeff https://ai.google/research/people/jeff 2: https://ai.google/research/people/SanjayGhemawat https://ai.google/research/people/SanjayGhemawat