traces_sampler example doesn't match the actual context provided

[dmarkow]

Issue Description

The docs give an example on how to adjust the sample rate depending on the context. However, it appears the example doesn't match what ultimately gets reported in the Sentry dashboard.

Reproduction Steps

Add this config from the docs and you'll see that the op is never http.server for any http requests, but instead atoms like :GET and :POST

config :sentry,
  traces_sampler: fn sampling_context ->
    case sampling_context.transaction_context.op do
      IO.inspect(op, label: "Actual op") 
      "http.server" -> 0.1  # Sample 10% of HTTP requests
      _ -> 0.05             # Sample 5% of other operations
    end
  end

Expected Behavior

Sample code should work, or docs should be updated to match what the library actually does.

Actual Behavior

100% of the traces reported by my Phoenix app show up with an op of either db or http.server on the Sentry dashboard. But the op field in the context passed to traces_sampler is always something more detailed. For example, if I issue a GET request to /health-check, this is what the context actually looks like when I inspect it.

%{
  attributes: %{
    "url.path": "/health-check",
    "http.request.method": :GET,
    "client.address": "127.0.0.1",
    "network.peer.address": "127.0.0.1",
    "network.peer.port": 62201,
    "network.protocol.version": :"1.1",
    "url.scheme": :http,
    "user_agent.original": "curl/8.7.1",
    "server.address": "localhost",
    "server.port": 4001
  },
  name: :GET,
  op: :GET,
  trace_id: 68167592341524485616445320670865761234
}

However, in Sentry's dashboard, this shows up like this, with an op of http.server.

So if I try to filter on http.server like the example shows, it doesn't work because op doesn't become http.server until some point after the traces_sampler function runs.

The same issue for db ops. In the context, they will show up as my_app.repo.query but report as db on the dashboard.

Elixir Version

1.18.4

SDK Version

11.0.4

Integration and Its Version

No response

Sentry Config

No response

[linear]

ELIXIR-38 traces_sampler example doesn't match the actual context provided

[solnic]

@dmarkow thanks for reporting this and apologies for the late reply - I'll update the docs and try to improve the DX eventually. For now the sampler operates at a lower level hence the discrapency.

[wingyplus]

Hi, I ran into this issue as well.

Possible to use span_kind instead of span_name? (see from https://github.com/getsentry/sentry-elixir/blob/master/lib/sentry/opentelemetry/sampler.ex#L134).

Or do you have any design in mind? I can help take a look.