feat(tag_cardinality_limit transform): enable per metric limits for tag_cardinality_limit

changelog.d/22077_per_metric_limits_for_tag_cardinality_limit_transform.feature.md

@@ -0,0 +1,3 @@
+The `tag_cardinality_limit` transform now supports customizing limits for specific metrics, matched by metric name and optionally its namespace.
+
+authors: esensar

src/transforms/tag_cardinality_limit/config.rs

@@ -16,6 +16,22 @@ use vector_lib::configurable::configurable_component;
 ))]
 #[derive(Clone, Debug)]
 pub struct TagCardinalityLimitConfig {
+    #[serde(flatten)]
+    pub global: TagCardinalityLimitInnerConfig,
+
+    /// Tag cardinality limits configuration per metric name.
+    #[configurable(
+        derived,
+        metadata(docs::additional_props_description = "An individual metric configuration.")
+    )]
+    #[serde(default)]
+    pub per_metric_limits: HashMap<String, PerMetricConfig>,
+}
+
+/// Configuration for the `tag_cardinality_limit` transform for a specific group of metrics.
+#[configurable_component]
+#[derive(Clone, Debug)]
+pub struct TagCardinalityLimitInnerConfig {
     /// How many distinct values to accept for any given key.
     #[serde(default = "default_value_limit")]
     pub value_limit: usize,
@@ -77,6 +93,18 @@ pub enum LimitExceededAction {
     DropEvent,
 }
 
+/// Tag cardinality limit configuration per metric name.
+#[configurable_component]
+#[derive(Clone, Debug)]
+pub struct PerMetricConfig {
+    /// Namespace of the metric this configuration refers to.
+    #[serde(default)]
+    pub namespace: Option<String>,
+
+    #[serde(flatten)]
+    pub config: TagCardinalityLimitInnerConfig,
+}
+
 const fn default_limit_exceeded_action() -> LimitExceededAction {
     LimitExceededAction::DropTag
 }
@@ -92,9 +120,12 @@ pub(crate) const fn default_cache_size() -> usize {
 impl GenerateConfig for TagCardinalityLimitConfig {
     fn generate_config() -> toml::Value {
         toml::Value::try_from(Self {
-            mode: Mode::Exact,
-            value_limit: default_value_limit(),
-            limit_exceeded_action: default_limit_exceeded_action(),
+            global: TagCardinalityLimitInnerConfig {
+                mode: Mode::Exact,
+                value_limit: default_value_limit(),
+                limit_exceeded_action: default_limit_exceeded_action(),
+            },
+            per_metric_limits: HashMap::default(),
         })
         .unwrap()
     }

src/transforms/tag_cardinality_limit/mod.rs

@@ -19,13 +19,15 @@ mod tag_value_set;
 mod tests;
 
 use crate::event::metric::TagValueSet;
-pub use config::TagCardinalityLimitConfig;
+pub use config::{TagCardinalityLimitConfig, TagCardinalityLimitInnerConfig};
 use tag_value_set::AcceptedTagValueSet;
 
+type MetricId = (Option<String>, String);
+
 #[derive(Debug)]
 pub struct TagCardinalityLimit {
     config: TagCardinalityLimitConfig,
-    accepted_tags: HashMap<String, AcceptedTagValueSet>,
+    accepted_tags: HashMap<Option<MetricId>, HashMap<String, AcceptedTagValueSet>>,
 }
 
 impl TagCardinalityLimit {
@@ -36,6 +38,24 @@ impl TagCardinalityLimit {
         }
     }
 
+    fn get_config_for_metric(
+        &self,
+        metric_key: Option<&MetricId>,
+    ) -> &TagCardinalityLimitInnerConfig {
+        match metric_key {
+            Some(id) => self
+                .config
+                .per_metric_limits
+                .iter()
+                .find(|(name, config)| {
+                    **name == id.1 && (config.namespace.is_none() || config.namespace == id.0)
+                })
+                .map(|(_, c)| &c.config)
+                .unwrap_or(&self.config.global),
+            None => &self.config.global,
+        }
+    }
+
     /// Takes in key and a value corresponding to a tag on an incoming Metric
     /// Event.  If that value is already part of set of accepted values for that
     /// key, then simply returns true.  If that value is not yet part of the
@@ -44,22 +64,29 @@ impl TagCardinalityLimit {
     /// for the key and returns true, otherwise returns false.  A false return
     /// value indicates to the caller that the value is not accepted for this
     /// key, and the configured limit_exceeded_action should be taken.
-    fn try_accept_tag(&mut self, key: &str, value: &TagValueSet) -> bool {
-        let tag_value_set = self.accepted_tags.entry_ref(key).or_insert_with(|| {
-            AcceptedTagValueSet::new(self.config.value_limit, &self.config.mode)
-        });
+    fn try_accept_tag(
+        &mut self,
+        metric_key: Option<&MetricId>,
+        key: &str,
+        value: &TagValueSet,
+    ) -> bool {
+        let config = self.get_config_for_metric(metric_key).clone();
+        let metric_accepted_tags = self.accepted_tags.entry(metric_key.cloned()).or_default();
+        let tag_value_set = metric_accepted_tags
+            .entry_ref(key)
+            .or_insert_with(|| AcceptedTagValueSet::new(config.value_limit, &config.mode));
 
         if tag_value_set.contains(value) {
             // Tag value has already been accepted, nothing more to do.
             return true;
         }
 
         // Tag value not yet part of the accepted set.
-        if tag_value_set.len() < self.config.value_limit {
+        if tag_value_set.len() < config.value_limit {
             // accept the new value
             tag_value_set.insert(value.clone());
 
-            if tag_value_set.len() == self.config.value_limit {
+            if tag_value_set.len() == config.value_limit {
                 emit!(TagCardinalityValueLimitReached { key });
             }
 
@@ -72,34 +99,57 @@ impl TagCardinalityLimit {
 
     /// Checks if recording a key and value corresponding to a tag on an incoming Metric would
     /// exceed the cardinality limit.
-    fn tag_limit_exceeded(&self, key: &str, value: &TagValueSet) -> bool {
+    fn tag_limit_exceeded(
+        &self,
+        metric_key: Option<&MetricId>,
+        key: &str,
+        value: &TagValueSet,
+    ) -> bool {
         self.accepted_tags
-            .get(key)
-            .map(|value_set| {
-                !value_set.contains(value) && value_set.len() >= self.config.value_limit
+            .get(&metric_key.cloned())
+            .and_then(|metric_accepted_tags| {
+                metric_accepted_tags.get(key).map(|value_set| {
+                    !value_set.contains(value)
+                        && value_set.len() >= self.get_config_for_metric(metric_key).value_limit
+                })
             })
             .unwrap_or(false)
     }
 
     /// Record a key and value corresponding to a tag on an incoming Metric.
-    fn record_tag_value(&mut self, key: &str, value: &TagValueSet) {
-        self.accepted_tags
+    fn record_tag_value(&mut self, metric_key: Option<&MetricId>, key: &str, value: &TagValueSet) {
+        let config = self.get_config_for_metric(metric_key).clone();
+        let metric_accepted_tags = self.accepted_tags.entry(metric_key.cloned()).or_default();
+        metric_accepted_tags
             .entry_ref(key)
-            .or_insert_with(|| AcceptedTagValueSet::new(self.config.value_limit, &self.config.mode))
+            .or_insert_with(|| AcceptedTagValueSet::new(config.value_limit, &config.mode))
             .insert(value.clone());
     }
 
     fn transform_one(&mut self, mut event: Event) -> Option<Event> {
         let metric = event.as_mut_metric();
         let metric_name = metric.name().to_string();
+        let metric_namespace = metric.namespace().map(|n| n.to_string());
+        let has_per_metric_config = self.config.per_metric_limits.iter().any(|(name, config)| {
+            *name == metric_name
+                && (config.namespace.is_none() || config.namespace == metric_namespace)
+        });
+        let metric_key = if has_per_metric_config {
+            Some((metric_namespace, metric_name.clone()))
+        } else {
+            None
+        };
         if let Some(tags_map) = metric.tags_mut() {
-            match self.config.limit_exceeded_action {
+            match self
+                .get_config_for_metric(metric_key.as_ref())
+                .limit_exceeded_action
+            {
                 LimitExceededAction::DropEvent => {
                     // This needs to check all the tags, to ensure that the ordering of tag names
                     // doesn't change the behavior of the check.
 
                     for (key, value) in tags_map.iter_sets() {
-                        if self.tag_limit_exceeded(key, value) {
+                        if self.tag_limit_exceeded(metric_key.as_ref(), key, value) {
                             emit!(TagCardinalityLimitRejectingEvent {
                                 metric_name: &metric_name,
                                 tag_key: key,
@@ -109,12 +159,12 @@ impl TagCardinalityLimit {
                         }
                     }
                     for (key, value) in tags_map.iter_sets() {
-                        self.record_tag_value(key, value);
+                        self.record_tag_value(metric_key.as_ref(), key, value);
                     }
                 }
                 LimitExceededAction::DropTag => {
                     tags_map.retain(|key, value| {
-                        if self.try_accept_tag(key, value) {
+                        if self.try_accept_tag(metric_key.as_ref(), key, value) {
                             true
                         } else {
                             emit!(TagCardinalityLimitRejectingTag {