Insert the cache entry logging.

linera-views/src/backends/lru_caching.rs

@@ -29,7 +29,10 @@ use std::{
 
 use linked_hash_map::LinkedHashMap;
 #[cfg(with_metrics)]
-use {linera_base::prometheus_util, prometheus::IntCounterVec};
+use {
+    linera_base::prometheus_util,
+    prometheus::{HistogramVec, IntCounterVec},
+};
 
 #[cfg(with_testing)]
 use crate::memory::MemoryStore;
@@ -85,6 +88,36 @@ static NUM_CACHE_FIND_SUCCESS: LazyLock<IntCounterVec> = LazyLock::new(|| {
     .expect("Counter creation should not fail")
 });
 
+#[cfg(with_metrics)]
+/// Size of the inserted value entry
+static VALUE_CACHE_ENTRY_SIZE: LazyLock<HistogramVec> = LazyLock::new(|| {
+    prometheus_util::register_histogram_vec(
+        "value_cache_entry_size",
+        "Value cache entry size",
+        &[],
+        Some(vec![
+            10.0, 30.0, 100.0, 300.0, 1000.0, 3000.0, 10000.0, 30000.0, 100000.0, 300000.0,
+            1000000.0,
+        ]),
+    )
+    .expect("Histogram can be created")
+});
+
+#[cfg(with_metrics)]
+/// Size of the inserted find entry
+static FIND_CACHE_ENTRY_SIZE: LazyLock<HistogramVec> = LazyLock::new(|| {
+    prometheus_util::register_histogram_vec(
+        "find_cache_entry_size",
+        "Find cache entry size",
+        &[],
+        Some(vec![
+            10.0, 30.0, 100.0, 300.0, 1000.0, 3000.0, 10000.0, 30000.0, 100000.0, 300000.0,
+            1000000.0,
+        ]),
+    )
+    .expect("Histogram can be created")
+});
+
 #[derive(Clone, Hash, Eq, PartialEq, Ord, PartialOrd)]
 enum CacheEntry {
     Find,
@@ -445,6 +478,10 @@ impl LruPrefixCache {
     /// Inserts a value entry into the cache.
     pub fn insert_value(&mut self, key: Vec<u8>, cache_entry: ValueCacheEntry) {
         let cache_size = cache_entry.size() + key.len();
+        #[cfg(with_metrics)]
+        VALUE_CACHE_ENTRY_SIZE
+            .with_label_values(&[])
+            .observe(cache_size as f64);
         if cache_size > self.lru_cache_policy.max_cache_size {
             // Inserting that entry would lead to complete clearing of the cache
             // which is counterproductive
@@ -487,6 +524,10 @@ impl LruPrefixCache {
     /// Inserts a find entry into the cache.
     pub fn insert_find(&mut self, key_prefix: Vec<u8>, cache_entry: FindCacheEntry) {
         let cache_size = cache_entry.size() + key_prefix.len();
+        #[cfg(with_metrics)]
+        FIND_CACHE_ENTRY_SIZE
+            .with_label_values(&[])
+            .observe(cache_size as f64);
         if cache_size > self.lru_cache_policy.max_cache_size {
             // Inserting that entry would lead to complete clearing of the cache
             // which is counter productive
@@ -506,7 +547,7 @@ impl LruPrefixCache {
             let keys = self
                 .map_value
                 .range(get_interval(key_prefix.clone()))
-                .map(|(x,_)| x.clone())
+                .map(|(x, _)| x.clone())
                 .collect::<Vec<_>>();
             for key in keys {
                 self.map_value.remove(&key);