enhancement(tag_cardinality_limit transform): Remove HashSet initialization with capacity to improve memory usage (#25480)

Remove HashSet initialization with capacity

Author: ArunPiduguDD

changelog.d/tag_cardinality_limit_improve_memory_usage.enhancement.md

@@ -0,0 +1,3 @@
+Reduce the memory usage of the `tag_cardinality_limit` transform when running in `exact` mode by allocating less unused memory on initialization.
+
+authors: ArunPiduguDD

src/transforms/tag_cardinality_limit/mod.rs

@@ -213,7 +213,7 @@ impl TagCardinalityLimit {
         let metric_accepted_tags = self.accepted_tags.entry(metric_key_owned).or_default();
         let tag_value_set = metric_accepted_tags
             .entry_ref(key)
-            .or_insert_with(|| AcceptedTagValueSet::new(config.value_limit, &config.mode));
+            .or_insert_with(|| AcceptedTagValueSet::new(&config.mode));
 
         if tag_value_set.contains(value) {
             // Tag value has already been accepted, nothing more to do.
@@ -300,7 +300,7 @@ impl TagCardinalityLimit {
         let metric_accepted_tags = self.accepted_tags.entry(metric_key_owned).or_default();
         metric_accepted_tags
             .entry_ref(key)
-            .or_insert_with(|| AcceptedTagValueSet::new(config.value_limit, &config.mode))
+            .or_insert_with(|| AcceptedTagValueSet::new(&config.mode))
             .insert(value.clone());
         false
     }

src/transforms/tag_cardinality_limit/tag_value_set.rs

@@ -59,9 +59,9 @@ impl fmt::Debug for TagValueSetStorage {
 }
 
 impl AcceptedTagValueSet {
-    pub fn new(value_limit: usize, mode: &Mode) -> Self {
+    pub fn new(mode: &Mode) -> Self {
         let storage = match &mode {
-            Mode::Exact => TagValueSetStorage::Set(HashSet::with_capacity(value_limit)),
+            Mode::Exact => TagValueSetStorage::Set(HashSet::new()),
             Mode::Probabilistic(config) => {
                 TagValueSetStorage::Bloom(BloomFilterStorage::new(config.cache_size_per_key))
             }
@@ -100,7 +100,7 @@ mod tests {
 
     #[test]
     fn test_accepted_tag_value_set_exact() {
-        let mut accepted_tag_value_set = AcceptedTagValueSet::new(2, &Mode::Exact);
+        let mut accepted_tag_value_set = AcceptedTagValueSet::new(&Mode::Exact);
 
         assert!(!accepted_tag_value_set.contains(&TagValueSet::from(["value1".to_string()])));
         assert_eq!(accepted_tag_value_set.len(), 0);
@@ -116,7 +116,7 @@ mod tests {
 
     #[test]
     fn test_accepted_tag_value_set_probabilistic() {
-        let mut accepted_tag_value_set = AcceptedTagValueSet::new(2, &Mode::Exact);
+        let mut accepted_tag_value_set = AcceptedTagValueSet::new(&Mode::Exact);
 
         assert!(!accepted_tag_value_set.contains(&TagValueSet::from(["value1".to_string()])));
         assert_eq!(accepted_tag_value_set.len(), 0);