Now that we've seen a bit about how the cacheability metadata can be used in more common scenarios, let's shift gears and talk about those page components that have highly dynamic data.
When we set the maximum age of our Hello World salutation to 0 seconds (don't cache), I mentioned that there are ways this can be improved in order to help performance. This involves postponing the rendering of the respective bit to the very last moment with the help of placeholders. But first, a bit of background.
Each of the cache properties we talked about can have values that make caching the render array pointless. We've already talked about the maximum age being set to 0, but you can also argue very low expiration times to have the same effect. Additionally, certain cache tags can be invalidated too frequently, again making the render arrays...