add DD_TRACE_STATS_ADDITIONAL_TAGS_CARDINALITY_LIMIT

Author: duncanpharvey

crates/datadog-trace-agent/src/config.rs

@@ -115,7 +115,10 @@ pub struct Config {
     pub proxy_url: Option<String>,
     pub env: String,
     pub peer_tags: Vec<String>,
+    /// Tag keys extracted from spans and used as additional aggregation dimensions in stats.
     pub additional_metric_tags: Vec<String>,
+    /// Configures the per-bucket cardinality limit for additional_metric_tags stat entries.
+    pub additional_metric_tags_cardinality_limit: Option<usize>,
     /// Whether the agent should compute trace stats
     pub agent_stats_computation_enabled: bool,
 }
@@ -268,6 +271,12 @@ impl Config {
                 .filter(|s| !s.is_empty())
                 .map(|s| s.split(',').map(str::to_owned).collect())
                 .unwrap_or_default(),
+            additional_metric_tags_cardinality_limit: env::var(
+                "DD_TRACE_STATS_ADDITIONAL_TAGS_CARDINALITY_LIMIT",
+            )
+            .ok()
+            .and_then(|s| s.parse::<usize>().ok())
+            .filter(|&n| n > 0),
             agent_stats_computation_enabled: env::var("DD_AGENT_STATS_COMPUTATION_ENABLED")
                 .map(|val| val.to_lowercase() == "true")
                 .unwrap_or(false),
@@ -789,6 +798,7 @@ pub mod test_helpers {
             env: "none".to_string(),
             peer_tags: peer_tag_keys().unwrap(),
             additional_metric_tags: vec![],
+            additional_metric_tags_cardinality_limit: None,
             agent_stats_computation_enabled: false,
         }
     }

crates/datadog-trace-agent/src/stats_concentrator_service.rs

@@ -84,8 +84,9 @@ impl StatsConcentratorService {
     fn new_span_concentrator(
         peer_tags: Vec<String>,
         additional_metric_tags: Vec<String>,
+        additional_metric_tags_cardinality_limit: Option<usize>,
     ) -> SpanConcentrator {
-        SpanConcentrator::new(
+        let mut concentrator = SpanConcentrator::new(
             Duration::from_nanos(BUCKET_DURATION_NS),
             SystemTime::now(),
             SPAN_KINDS_STATS_COMPUTED
@@ -94,7 +95,11 @@ impl StatsConcentratorService {
                 .collect(),
             peer_tags,
             additional_metric_tags,
-        )
+        );
+        if let Some(limit) = additional_metric_tags_cardinality_limit {
+            concentrator.set_additional_metric_tags_cardinality_limit(limit);
+        }
+        concentrator
     }
 
     pub async fn run(mut self) {
@@ -114,6 +119,7 @@ impl StatsConcentratorService {
                             Self::new_span_concentrator(
                                 config.peer_tags.clone(),
                                 config.additional_metric_tags.clone(),
+                                config.additional_metric_tags_cardinality_limit,
                             )
                         });