Simplify and make sample rand docs more specific #12327
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jan-auer
approved these changes
Jan 14, 2025
| The random value is set according to the following rules: | ||
| 1. When tracing is enabled and a new trace is started, the SDK generates a `sample_rand` value for the current execution context. A `sample_rand` is a float (`0.1234` notation) in the range of `[0, 1)` (including 0.0, excluding 1.0). | ||
| 1. It is _recommended_ to generate the random number deterministically using the trace ID as seed or source of randomness. The exact method by which the random number is created is implementation defined and may vary between SDK implementations. | ||
| 1. The `sample_rand` is part of the DSC (Dynamic Sampling Context) and as with other values on the `baggage` header, the `sentry-sample_rand` value from the current execution context should be propagated to downstream SDKs. |
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| 1. The `sample_rand` is part of the DSC (Dynamic Sampling Context) and as with other values on the `baggage` header, the `sentry-sample_rand` value from the current execution context should be propagated to downstream SDKs. | |
| 1. The `sample_rand` is part of the DSC (Dynamic Sampling Context) and as with other values on the `baggage` header, the `sample_rand` value from the current execution context should be propagated to downstream SDKs. |
| The SDK should always use the stored random number (`sentry-sample_rand`) for sampling decisions and should no longer rely on `math.random()` or similar functions in tracing code: | ||
| 1. When the `tracesSampler` is invoked, the return value should be compared with `sample_rand`: `trace["sentry-sample_rand"] < tracesSampler(context)` | ||
| 1. When the SDK is the head of a trace (and `tracesSampleRate` is defined), the sampling is done comparing the `tracesSampleRate` with the `sample_rand`: `trace["sentry-sample_rand"] < config.tracesSampleRate` | ||
| 1. If no `tracesSampler` callback is configured, the SDK fully inherits incoming sampling decisions from the `sentry-trace` header for propagated traces. |
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| 1. If no `tracesSampler` callback is configured, the SDK fully inherits incoming sampling decisions from the `sentry-trace` header for propagated traces. | |
| 1. Otherwise, there is an incoming trace and the SDK fully inherits incoming sampling decisions from the `sentry-trace` header for propagated traces. |
You might also turn 2 and 3 around for clarity to say:
- if tracesSampler, ...
- if there's an incoming trace, ...
- otherwise, the SDK is the head of the trace, ...
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Adjusts the dev docs on sample_rand to require 30 less IQ points when reading. I used myself (borderline dyslexic) as a benchmark.