follow Prometheus naming conventions for new metric names

Author: fstab

simpleclient_hotspot/src/main/java/io/prometheus/client/hotspot/MemoryPoolsExports.java

@@ -88,6 +88,11 @@ void addMemoryAreaMetrics(List<MetricFamilySamples> sampleFamilies) {
   }
 
   void addMemoryPoolMetrics(List<MetricFamilySamples> sampleFamilies) {
+
+    // Note: The Prometheus naming convention is that units belong at the end of the metric name.
+    // For new metrics like jvm_memory_pool_collection_used_bytes we follow that convention.
+    // For old metrics like jvm_memory_pool_bytes_used we keep the names as they are to avoid a breaking change.
+
     GaugeMetricFamily used = new GaugeMetricFamily(
         "jvm_memory_pool_bytes_used",
         "Used bytes of a given JVM memory pool.",
@@ -109,22 +114,22 @@ void addMemoryPoolMetrics(List<MetricFamilySamples> sampleFamilies) {
         Collections.singletonList("pool"));
     sampleFamilies.add(init);
     GaugeMetricFamily collectionUsed = new GaugeMetricFamily(
-        "jvm_memory_pool_collection_bytes_used",
+        "jvm_memory_pool_collection_used_bytes",
         "Used bytes after last collection of a given JVM memory pool.",
         Collections.singletonList("pool"));
     sampleFamilies.add(collectionUsed);
     GaugeMetricFamily collectionCommitted = new GaugeMetricFamily(
-        "jvm_memory_pool_collection_bytes_committed",
+        "jvm_memory_pool_collection_committed_bytes",
         "Committed after last collection bytes of a given JVM memory pool.",
         Collections.singletonList("pool"));
     sampleFamilies.add(collectionCommitted);
     GaugeMetricFamily collectionMax = new GaugeMetricFamily(
-        "jvm_memory_pool_collection_bytes_max",
+        "jvm_memory_pool_collection_max_bytes",
         "Max bytes after last collection of a given JVM memory pool.",
         Collections.singletonList("pool"));
     sampleFamilies.add(collectionMax);
     GaugeMetricFamily collectionInit = new GaugeMetricFamily(
-        "jvm_memory_pool_collection_bytes_init",
+        "jvm_memory_pool_collection_init_bytes",
         "Initial after last collection bytes of a given JVM memory pool.",
         Collections.singletonList("pool"));
     sampleFamilies.add(collectionInit);

simpleclient_hotspot/src/test/java/io/prometheus/client/hotspot/MemoryPoolsExportsTest.java

@@ -90,28 +90,28 @@ public void testMemoryPools() {
     assertEquals(
         400000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_used",
+            "jvm_memory_pool_collection_used_bytes",
             new String[]{"pool"},
             new String[]{"PS Eden Space"}),
         .0000001);
     assertEquals(
         800000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_committed",
+            "jvm_memory_pool_collection_committed_bytes",
             new String[]{"pool"},
             new String[]{"PS Eden Space"}),
         .0000001);
     assertEquals(
         1600000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_max",
+            "jvm_memory_pool_collection_max_bytes",
             new String[]{"pool"},
             new String[]{"PS Eden Space"}),
         .0000001);
     assertEquals(
         2000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_init",
+            "jvm_memory_pool_collection_init_bytes",
             new String[]{"pool"},
             new String[]{"PS Eden Space"}),
         .0000001);
@@ -146,28 +146,28 @@ public void testMemoryPools() {
     assertEquals(
         20000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_used",
+            "jvm_memory_pool_collection_used_bytes",
             new String[]{"pool"},
             new String[]{"PS Old Gen"}),
         .0000001);
     assertEquals(
         40000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_committed",
+            "jvm_memory_pool_collection_committed_bytes",
             new String[]{"pool"},
             new String[]{"PS Old Gen"}),
         .0000001);
     assertEquals(
         6000000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_max",
+            "jvm_memory_pool_collection_max_bytes",
             new String[]{"pool"},
             new String[]{"PS Old Gen"}),
         .0000001);
     assertEquals(
         4000L,
         registry.getSampleValue(
-            "jvm_memory_pool_collection_bytes_init",
+            "jvm_memory_pool_collection_init_bytes",
             new String[]{"pool"},
             new String[]{"PS Old Gen"}),
         .0000001);