Cache that DNS UDP query led to TC

[miekg]

Currently the code in retrieval/discovery/dns.go always does a UDP lookup first. When this returns a truncated packet, a TCP query is tried instead. So far so good.

I think it makes sense to implement some kind of caching here, so once a TC bit is seen for a name, only TCP queries are done for the next X minutes (or whatever).

[fabxc]

That's certainly an optimization we should consider.
I don't think it's urgent for now, though, as the number of DNS requests is
completely shadowed by the number of target scrapes.

It might take a while until we get to it – PRs are always welcome, of
course :)

On Wed, May 27, 2015 at 4:20 PM Miek Gieben notifications@github.com
wrote:

Currently the code in retrieval/discovery/dns.go always does a UDP lookup
first. When this returns a truncated packet, a TCP query is tried instead.
So far so good.

I think it makes sense to implement some kind of caching here, so once a
TC bit is seen for a name, only TCP queries are done for the next X minutes
(or whatever).

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