Documentation Grafana Cloud Adaptive Telemetry Adaptive Traces Guides Policy evaluation example

How policies are evaluated

When a trace is received, it is evaluated against all your policies at once to make a single, final decision: keep (sample) or drop. The logic follows two core principles.

Principle 1: Keep if it matches any keep policy (the “or” logic)

Think of your keep policies as a giant OR condition. A trace only needs to match one of these policies to be flagged for keeping. It does not need to match all of them.

For example, if you have these policies:

• Keep traces with errors.
• Keep traces with latency > 2 seconds.
• Keep 10% of all remaining traces.

A trace with an error is kept.

A trace with a 3-second latency is kept. It does not matter if the slow trace also had an error; one match is enough.

The 10% probabilistic policy acts as a catch-all for traces that do not match any of your more specific rules.

Principle 2: Drop always wins

A drop policy is an absolute veto. If a trace matches any drop policy, it is discarded immediately, even if it also matches one or more keep policies.

For example, imagine you add this policy:

• Drop all traces from the /grafana endpoint.

If a slow, erroneous trace comes from the /grafana endpoint, it is dropped. The drop rule takes priority over all keep rules.

Example

Let’s look at how the system evaluates a few different traces with the policies from above.

In summary, just remember these rules.

• A trace is evaluated against all policies at once. A trace is kept if it matches at least one keep policy.
• A trace is dropped if it matches any drop policy.
• If a trace matches both a keep and a drop policy, drop always wins.

Policy example using code

The following code snippet is example of how the policies above can be defined using JSON.

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# Policy 1: Keep traces with latency > 2 seconds

{
  "threshold_ms": 2000,
}


# Policy 2: Keep 10% of all traces as a general sample

{
  "sampling_percentage": 10
}

# Policy 3: Drop all traces from the /grafana endpoint

{
    "drop_sub_policy": [
    {
      "name": "healthcheck-drop",
      "type": "string_attribute",
      "string_attribute": {
        "key": "http.target",
        "values": [
          "/grafana"
        ]
      }
    }
  ]
}

# Policy 4: Keep all traces that have an error

{
      "name": "error-keep",
      "type": "status_code",
 "status_codes": [
    "ERROR"
  ]
}

How to interpret this code

1. List of Policies: The system evaluates a trace against this entire list.
2. Drop: The healthcheck-drop policy is explicitly configured to action: drop. When a trace with http.target: /grafana is processed, this rule provides the definitive drop decision that overrides any keep decisions from other policies.
3. Keep: For a trace that is not dropped, the system only needs one of the other policies. For example, high-latency-keep, error-keep, or probabilistic-catch-all to return a keep decision.