[adrianmonk]

Aren't misses pretty preventable?

The only reason the client is even asking is that the server sent them a header saying it might be beneficial to do so.

And the client definitely has the dictionary data. The only thing it needs is for the server to accommodate the request after leading it down that path in the first place.

I can picture how it could happen, though. If you didn't realize the cost, you might not try to prevent misses. Or you could have a configuration error like sending the header but forgetting to generate pre-compressed data in your build.

If this is a significant issue, a server could collect stats and generate warnings about situations where it's not pulling its weight. Or even automatically disable it if hit rates are terrible.