Hello. I'd like to understand correctly and precisely the meaning of the _prefetch_ server config option. The only documentation I've been able to find is the unbound.conf manpage, which has this to say:
prefetch: <yes or no> If yes, message cache elements are prefetched before they expire to keep the cache up to date. Default is no. Turning it on gives about 10 percent more traffic and load on the machine, but popular items do not expire from the cache. This is clear but not precise enough. Under what circumstances are cache entries refreshed? Do they have to be close to expiration? How close? Or is there some other condition that triggers a refresh? And then there is the _minimal-responses_ option. I have a good idea what it does, by itself, but the documentation helpfully drags in prefetching again: minimal-responses: <yes or no> If yes, Unbound does not insert authority/additional sections into response messages when those sections are not required. This reduces response size significantly, and may avoid TCP fallback for some responses. This may cause a slight speedup. The default is yes, even though the DNS protocol RFCs mandate these sections, and the additional content could be of use and save roundtrips for clients. Because they are not used, and the saved roundtrips are easier saved with prefetch, whilst this is faster. That last sentence sounds like Google Translate before LLM era :-( What's "they" and "this" there? Why is prefetch "easier", given the 10 percent figure in the quote above? -- Ian
