When my database write latency spiked by 340% after crossing 50 million rows, my CPU wasn't maxed out. My queries weren't missing indexes. Instead, my storage IOPS was completely saturated by a single architectural default I set up on day one: using UUIDv4 as my primary key.
Source: [Dev.to](https://dev.to/johnnylemonny/uuidv4-is-not-free-why-random-primary-keys-are-silently-crushing-your-write-performance-2ea8)