Add Dns event counters

[stephentoub]

We should consider adding some event counters around name resolution, e.g.

• Number of Dns requests issued
• Number of Dns requests currently in fight
• Number of unique Dns requests currently in flight

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Issue Details

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We should consider adding some event counters around name resolution, e.g.

• Number of Dns requests issued
• Number of Dns requests currently in fight
• Number of unique Dns requests currently in flight

Author:	stephentoub
Assignees:	-
Labels:	area-System.Net
Milestone:	6.0.0

[MihaZupan]

Right now we have

• dns-lookups-requested - DNS Lookups Requested (total counter)
• dns-lookups-duration - Average DNS Lookup Duration

Number of Dns requests currently in fight

Something like current-dns-lookups seems reasonable - we have that for Net.Security and Net.Http as well.

With #48566 in mind, the meaning of this would likely be "number of not-finished Dns.Foo(...) calls".

Number of unique Dns requests currently in flight

I assume the tracking of "unique" would be duplicated between the Telemetry impl and a potential #48566 impl?

[stephentoub]

dns-lookups-requested

Ah, I didn't see that one. That's the "Number of Dns requests issued" I was asking for.

Something like current-dns-lookups seems reasonable ... the meaning of this would likely be "number of not-finished Dns.Foo(...) calls"

Yes, if we're already tracking number of requests initiated, then if we also tracked number of requests finished, it would be the difference.

I assume the tracking of "unique" would be duplicated between the Telemetry impl and a potential #48566 impl?

There might be some duplication, but whatever we do for #48566 is likely to only apply to a portion of requests, e.g. those that are implemented by queueing work items to the thread pool. On Windows most if not all requests will instead be implemented with async OS functionality, and we wouldn't do any such uniqueness tracking for the implementation. Longer term, we'd expect that to be true for all OSes.

[ManickaP]

Triage: shouldn't be hard to implement, the numbers might be useful. We would want current-dns-lookups for 6.0.

[MihaZupan]

Currently implemented:

• Start/Failed/Stop events
  • Failed could use some additional info such as the exception message - right now it's just an empty event
• dns-lookups-requested (total for process)
• current-dns-lookups (current)
• dns-lookups-duration (average time taken for lookups within the last counter period)

Not yet added:

• Number of unique DNS requests currently in flight

Potential:

• Number of unique DNS addresses resolved in an application’s lifetime (from Additional diagnostics for .NET 6 #56072)