Stats Traffic: Prefetching and caching improvements

[staskus]

Possible improvements:

• Skip refreshing data if cached data exists for the past period
• Consider prefetching the previous period once the current period loads
• Consider prefetching different data range once the current data range and period loads

[dangermattic]

Thanks for reporting! 👍

[staskus]

No longer relevant. We'll likely make changes to date-picking in general which would require completely different caching strategies.