Change caffeine_cache_eviction_weight from Gauge to Counter

Signed-off-by: Jean Hominal <[email protected]>

Author: jhominal

prometheus-metrics-instrumentation-caffeine/src/main/java/io/prometheus/metrics/instrumentation/caffeine/CacheMetricsCollector.java

@@ -146,10 +146,10 @@ public MetricSnapshots collect() {
             .name(METRIC_NAME_CACHE_EVICTION)
             .help("Cache eviction totals, doesn't include manually removed entries");
 
-    final GaugeSnapshot.Builder cacheEvictionWeight =
-        GaugeSnapshot.builder()
+    final CounterSnapshot.Builder cacheEvictionWeight =
+        CounterSnapshot.builder()
             .name(METRIC_NAME_CACHE_EVICTION_WEIGHT)
-            .help("Cache eviction weight");
+            .help("Weight of evicted cache entries, doesn't include manually removed entries");
 
     final CounterSnapshot.Builder cacheLoadFailure =
         CounterSnapshot.builder().name(METRIC_NAME_CACHE_LOAD_FAILURE).help("Cache load failures");
@@ -175,7 +175,7 @@ public MetricSnapshots collect() {
 
       try {
         cacheEvictionWeight.dataPoint(
-            GaugeSnapshot.GaugeDataPointSnapshot.builder()
+            CounterSnapshot.CounterDataPointSnapshot.builder()
                 .labels(labels)
                 .value(stats.evictionWeight())
                 .build());

prometheus-metrics-instrumentation-caffeine/src/test/java/io/prometheus/metrics/instrumentation/caffeine/CacheMetricsCollectorTest.java

@@ -52,6 +52,7 @@ public void cacheExposesMetricsForHitMissAndEviction() {
     assertCounterMetric(registry, "caffeine_cache_miss", "users", 2.0);
     assertCounterMetric(registry, "caffeine_cache_requests", "users", 3.0);
     assertCounterMetric(registry, "caffeine_cache_eviction", "users", 2.0);
+    assertCounterMetric(registry, "caffeine_cache_eviction_weight", "users", 2.0);
 
     final String expected =
         "# TYPE caffeine_cache_estimated_size gauge\n"
@@ -60,9 +61,9 @@ public void cacheExposesMetricsForHitMissAndEviction() {
             + "# TYPE caffeine_cache_eviction counter\n"
             + "# HELP caffeine_cache_eviction Cache eviction totals, doesn't include manually removed entries\n"
             + "caffeine_cache_eviction_total{cache=\"users\"} 2.0\n"
-            + "# TYPE caffeine_cache_eviction_weight gauge\n"
-            + "# HELP caffeine_cache_eviction_weight Cache eviction weight\n"
-            + "caffeine_cache_eviction_weight{cache=\"users\"} 2.0\n"
+            + "# TYPE caffeine_cache_eviction_weight counter\n"
+            + "# HELP caffeine_cache_eviction_weight Weight of evicted cache entries, doesn't include manually removed entries\n"
+            + "caffeine_cache_eviction_weight_total{cache=\"users\"} 2.0\n"
             + "# TYPE caffeine_cache_hit counter\n"
             + "# HELP caffeine_cache_hit Cache hit totals\n"
             + "caffeine_cache_hit_total{cache=\"users\"} 1.0\n"