Generating Metrics subtracting the latency of a child span from the parent span - PERCENTILES

Grafana Tempo
1

Hi,
I’m using the Metrics-Generator and the span metrics processor.
The goal is the same described in this topic: subtracting the latency of a child span (for example the time spent calling an external service) from the latency of the parent span.
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For example, after the ingestion of metrics into Prometheus, the query below returns the difference between the parent span and the child span:

traces_spanmetrics_latency_sum{span_name="GET /open-telemetry-web/myapp/myrest"} - on () traces_spanmetrics_latency_sum{span_name="GET"}

so, it’s also possible calculate the average latency of the parent span without the latency of the child span:

(traces_spanmetrics_latency_sum{span_name="GET /open-telemetry-web/myapp/myrest"} - on () traces_spanmetrics_latency_sum{span_name="GET"} ) / on () traces_spanmetrics_latency_count{span_name="GET /open-telemetry-web/myapp/myrest"}

But what about percentiles? The metric traces_spanmetrics_latency_bucket can be used to calculate percentiles of single spans, but it can’t be used for calculating a percentile of the latency of the parent span without the latency of child span.