At Google, we like to use our own projects for internal development. Following that philosophy, one of the first apps ever made for Google App Engine was the contest platform for Google Code Jam. The application was a good fit: a rich web interface, real-time user interaction, and a heavily parallel design. But we faced one major challenge, which was how to handle the huge scoreboard -- in the first round, we had over 11,000 contestants.
While App Engine's datastore allows you to sort entities by score, it doesn't have a built-in mechanism to answer the following two requests:
To solve these issues, we came up with a library that maintains a data structure to efficiently support these use cases. We imagine that other applications will have similar problems (e.g., a high-score list in a game), and so we're happy to release our work as the "google-appengine-ranklist" library.
The library supports three different operations:
If you think this library could be useful for you, take a look at the documentation and at the example application. We'd love to hear from you in our Google Group.