At Facebook, noticing a sudden spike in DAUs in Indonesia, how would you investigate the cause?

To investigate a sudden spike in Indonesian DAUs, I would first define the scope by clarifying the timeframe (e.g., last 3 weeks) and the exact definition of a "Daily Active User" (e.g., app open, session duration, specific actions).

Then, I'd segment the data to identify which user groups, regions within Indonesia, or specific product features are driving the increase.

I would analyze external factors like major events, holidays, competitor activity, or marketing campaigns in Indonesia.

Simultaneously, I'd examine internal factors such as recent feature launches, app updates, or changes in our algorithms that might have positively impacted engagement.

Finally, I would cross-reference these findings to pinpoint the most probable cause(s) and validate them with A/B testing or further data analysis.