Optimizing Facebook for iOS start time

What this post added

This post details optimizations made to the Facebook for iOS app's start time, focusing on cold starts. Key contributions include: defining stable metrics for app start (from icon tap to feed loaded), breaking down cold start into request time, network time, and response processing time, identifying initialization as a bottleneck, refactoring feed request dependencies to allow concurrent initialization, implementing UDP priming to pre-fetch data and reduce TCP connection overhead, optimizing story fetching from a batch to a streaming approach (1+1+X), and deferring non-critical background services until after the feed is displayed to reduce contention.