feat(stats)!: add telemetry for per-field cardinality limits#2212
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feat(stats)!: add telemetry for per-field cardinality limits#2212Eldolfin wants to merge 16 commits into
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save memory by storing value hashes only, u64 has enough values to make collisions rare and in case we still get a collision storing 1 extra key should be fine
…alityLimitConfig binding
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paullegranddc
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Jul 8, 2026
| debug!( | ||
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||
| if total_collapsed.whole_key > 0 { | ||
| once!(debug!( |
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It must be emited once per flush period so no need to add a once macro
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| let collapsed_resources = handle.register_metric_context( | ||
| COLLAPSED_SPANS_TELEMETRY_METRIC.to_string(), | ||
| vec![libdd_common::tag!("collapsed_spans", "resource")], | ||
| libdd_telemetry::data::metrics::MetricType::Count, | ||
| true, | ||
| libdd_telemetry::data::metrics::MetricNamespace::Tracers, | ||
| ); | ||
| let collapsed_http_endpoints = handle.register_metric_context( | ||
| COLLAPSED_SPANS_TELEMETRY_METRIC.to_string(), | ||
| vec![libdd_common::tag!("collapsed_spans", "http_endpoint")], | ||
| libdd_telemetry::data::metrics::MetricType::Count, | ||
| true, | ||
| libdd_telemetry::data::metrics::MetricNamespace::Tracers, | ||
| ); | ||
| let collapsed_peer_tags = handle.register_metric_context( | ||
| COLLAPSED_SPANS_TELEMETRY_METRIC.to_string(), | ||
| vec![libdd_common::tag!("collapsed_spans", "peer_tags")], | ||
| libdd_telemetry::data::metrics::MetricType::Count, | ||
| true, | ||
| libdd_telemetry::data::metrics::MetricNamespace::Tracers, | ||
| ); | ||
| let collapsed_additional_tags = handle.register_metric_context( | ||
| COLLAPSED_SPANS_TELEMETRY_METRIC.to_string(), | ||
| vec![libdd_common::tag!( | ||
| "collapsed_spans", | ||
| "additional_metric_tags" | ||
| )], | ||
| libdd_telemetry::data::metrics::MetricType::Count, | ||
| true, | ||
| libdd_telemetry::data::metrics::MetricNamespace::Tracers, | ||
| ); |
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From the RFC
(Multiple
collapsed:tags should be added when more than one field is collapsed)
I think it means we should send a single count metric with all the offending fields in the bucket instead of separate count metrics. I think the reason is because otherwise COLLAPSED_SPANS_TELEMETRY_METRIC will not count the number of collapsed spans but the total number of fields collapsed.
| /// Maximum number of distinct aggregation keys this bucket will hold before collapsing new | ||
| /// ones into the overflow sentinel key. | ||
| cardinality_limits: CardinalityLimitConfig, | ||
| // HashSet of hashes of values so save memory, no need for total accuracy here |
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Maybe detail a bit more why it's not accurate and how much collision we can escape as it can be a bit confusing we reading the code
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What does this PR do?
Send telemetry about per-field cardinality collapses.
Motivation
CSS spec compliance.
Additional Notes
Not a fan of how much I need to duplicate some parts of the code. But I wanted to avoid using HashMaps everywhere and keep the changes simple.
Maybe some sort of macro magic can solve this ? But I'm afraid it might hurt readability even more. I'm open to suggestions
How to test the change?
Describe here in detail how the change can be validated.