The parameters for cache refreshes can be customized, depending on the resources we have/can get. Currently, it's retrieving data for most of the items every 2 hours (with exceptions like package versions which run daily and are terribly slow). Backend is caching data for PRs, bugs, and pre-calculated updates/overrides data for users visiting the app at least once in two weeks. The main storage is a PostgreSQL database, and optionally, if RAM is not an issue, we have a local memory-cached layer that can be enabled (we find it not necessary ATM).
There seems to be an issue bug caching, it's showing bugs I closed a few weeks ago.