Support custom histogram buckets for Prometheus Timer Metrics

docs/development/extensions-contrib/prometheus.md

@@ -40,7 +40,7 @@ All the configuration parameters for the Prometheus emitter are under `druid.emi
 | `druid.emitter.prometheus.strategy`           | The strategy to expose prometheus metrics. <br/>Should be one of `exporter` and `pushgateway`. Default strategy `exporter` would expose metrics for scraping purpose. Peon tasks (short-lived jobs) should use `pushgateway` strategy. | yes       | exporter                             |
 | `druid.emitter.prometheus.port`               | The port on which to expose the prometheus HTTPServer. Required if using `exporter` strategy.                                                                                                                                          | no        | none                                 |
 | `druid.emitter.prometheus.namespace`          | Optional metric namespace. Must match the regex `[a-zA-Z_:][a-zA-Z0-9_:]*`                                                                                                                                                             | no        | druid                                |
-| `druid.emitter.prometheus.dimensionMapPath`   | JSON file defining the Prometheus metric type, desired dimensions, help text, and conversionFactor for every Druid metric.                                                                                                             | no        | Default mapping provided. See below. |
+| `druid.emitter.prometheus.dimensionMapPath`   | JSON file defining the Prometheus metric type, desired dimensions, conversionFactor, histogram buckets and help text for every Druid metric.                                                                                                             | no        | Default mapping provided. See below. |
 | `druid.emitter.prometheus.addHostAsLabel`     | Flag to include the hostname as a prometheus label.                                                                                                                                                                                    | no        | false                                |
 | `druid.emitter.prometheus.addServiceAsLabel`  | Flag to include the druid service name (e.g. `druid/broker`, `druid/coordinator`, etc.) as a prometheus label.                                                                                                                         | no        | false                                |
 | `druid.emitter.prometheus.pushGatewayAddress` | Pushgateway address. Required if using `pushgateway` strategy.                                                                                                                                                                         | no        | none                                 |
@@ -80,7 +80,7 @@ All metric names and labels are reformatted to match Prometheus standards.
 Each metric to be collected by Prometheus must specify a type, one of `[timer, counter, guage]`. Prometheus Emitter expects this mapping to
 be provided as a JSON file.  Additionally, this mapping specifies which dimensions should be included for each metric.  Prometheus expects
 histogram timers to use Seconds as the base unit.  Timers which do not use seconds as a base unit can use the `conversionFactor` to set
-the base time unit. If the user does not specify their own JSON file, a default mapping is used.  All
+the base time unit. Histogram timers also support custom bucket configurations through the `histogramBuckets` parameter. If no custom buckets are provided, the following default buckets are used: `[0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0, 30.0, 60.0, 120.0, 300.0]`. If the user does not specify their own JSON file, a default mapping is used.  All
 metrics are expected to be mapped. Metrics which are not mapped will not be tracked.
 
 Prometheus metric path is organized using the following schema:
@@ -90,6 +90,7 @@ Prometheus metric path is organized using the following schema:
   "dimensions" : <dimension list>, 
   "type" : <timer|counter|gauge>, 
   "conversionFactor": <conversionFactor>, 
+  "histogramBuckets": <array of bucket values for timer metric>,
   "help" : <help text>
 }
 ```
@@ -100,6 +101,7 @@ For example:
   "dimensions" : ["dataSource", "type"],
   "type" : "timer",
   "conversionFactor": 1000.0,
+  "histogramBuckets": [0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0, 30.0, 60.0, 120.0, 300.0],
   "help": "Seconds taken to complete a query."
 }
 ```

extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/DimensionsAndCollector.java

@@ -26,12 +26,14 @@ public class DimensionsAndCollector
   private final String[] dimensions;
   private final SimpleCollector collector;
   private final double conversionFactor;
+  private final double[] histogramBuckets;
 
-  DimensionsAndCollector(String[] dimensions, SimpleCollector collector, double conversionFactor)
+  DimensionsAndCollector(String[] dimensions, SimpleCollector collector, double conversionFactor, double[] histogramBuckets)
   {
     this.dimensions = dimensions;
     this.collector = collector;
     this.conversionFactor = conversionFactor;
+    this.histogramBuckets = histogramBuckets;
   }
 
   public String[] getDimensions()
@@ -48,4 +50,9 @@ public double getConversionFactor()
   {
     return conversionFactor;
   }
+
+  public double[] getHistogramBuckets()
+  {
+    return histogramBuckets;
+  }
 }

extensions-contrib/prometheus-emitter/src/main/java/org/apache/druid/emitter/prometheus/Metrics.java

@@ -38,6 +38,7 @@
 import java.io.InputStream;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.SortedSet;
 import java.util.regex.Pattern;
@@ -108,15 +109,15 @@ public Metrics(String namespace, String path, boolean isAddHostAsLabel, boolean
             .namespace(namespace)
             .name(formattedName)
             .labelNames(dimensions)
-            .buckets(.1, .25, .5, .75, 1, 2.5, 5, 7.5, 10, 30, 60, 120, 300)
+            .buckets(metric.histogramBuckets)
             .help(metric.help)
             .register();
       } else {
         log.error("Unrecognized metric type [%s]", type);
       }
 
       if (collector != null) {
-        parsedRegisteredMetrics.put(name, new DimensionsAndCollector(dimensions, collector, metric.conversionFactor));
+        parsedRegisteredMetrics.put(name, new DimensionsAndCollector(dimensions, collector, metric.conversionFactor, metric.histogramBuckets));
       }
     }
     this.registeredMetrics = Collections.unmodifiableMap(parsedRegisteredMetrics);
@@ -153,19 +154,26 @@ public static class Metric
     public final Type type;
     public final String help;
     public final double conversionFactor;
+    public final double[] histogramBuckets;
 
     @JsonCreator
     public Metric(
         @JsonProperty("dimensions") SortedSet<String> dimensions,
         @JsonProperty("type") Type type,
         @JsonProperty("help") String help,
-        @JsonProperty("conversionFactor") double conversionFactor
+        @JsonProperty("conversionFactor") double conversionFactor,
+        @JsonProperty("histogramBuckets") List<Double> histogramBuckets
     )
     {
       this.dimensions = dimensions;
       this.type = type;
       this.help = help;
       this.conversionFactor = conversionFactor;
+      if (histogramBuckets != null && !histogramBuckets.isEmpty()) {
+        this.histogramBuckets = histogramBuckets.stream().mapToDouble(Double::doubleValue).toArray();
+      } else {
+        this.histogramBuckets = new double[] {0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0, 30.0, 60.0, 120.0, 300.0};
+      }
     }
 
     public enum Type

extensions-contrib/prometheus-emitter/src/test/java/org/apache/druid/emitter/prometheus/MetricsTest.java

@@ -41,6 +41,8 @@ public void testMetricsConfiguration()
     Assert.assertEquals("host_name", dimensions[2]);
     Assert.assertEquals("type", dimensions[3]);
     Assert.assertEquals(1000.0, dimensionsAndCollector.getConversionFactor(), 0.0);
+    double[] defaultHistogramBuckets = {0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0, 30.0, 60.0, 120.0, 300.0};
+    Assert.assertArrayEquals(defaultHistogramBuckets, dimensionsAndCollector.getHistogramBuckets(), 0.0);
     Assert.assertTrue(dimensionsAndCollector.getCollector() instanceof Histogram);
 
     DimensionsAndCollector d = metrics.getByName("segment/loadQueue/count", "historical");
@@ -67,6 +69,8 @@ public void testMetricsConfigurationWithExtraLabels()
     Assert.assertEquals("host_name", dimensions[3]);
     Assert.assertEquals("type", dimensions[4]);
     Assert.assertEquals(1000.0, dimensionsAndCollector.getConversionFactor(), 0.0);
+    double[] defaultHistogramBuckets = {0.1, 0.25, 0.5, 0.75, 1.0, 2.5, 5.0, 7.5, 10.0, 30.0, 60.0, 120.0, 300.0};
+    Assert.assertArrayEquals(defaultHistogramBuckets, dimensionsAndCollector.getHistogramBuckets(), 0.0);
     Assert.assertTrue(dimensionsAndCollector.getCollector() instanceof Histogram);
 
     DimensionsAndCollector d = metrics.getByName("segment/loadQueue/count", "historical");
@@ -106,8 +110,26 @@ public void testMetricsConfigurationWithNonExistentMetric()
   @Test
   public void testMetricsConfigurationWithUnSupportedType()
   {
-    Assert.assertThrows(ISE.class, () -> {
-      new Metrics("test_5", "src/test/resources/defaultMetricsTest.json", true, true, null);
+    ISE iseException = Assert.assertThrows(ISE.class, () -> {
+      new Metrics("test_5", "src/test/resources/defaultInvalidMetricsTest.json", true, true, null);
     });
+    Assert.assertEquals("Failed to parse metric configuration", iseException.getMessage());
   }
+
+  @Test
+  public void testMetricsConfigurationWithTimerHistogramBuckets()
+  {
+    Metrics metrics = new Metrics("test_6", "src/test/resources/defaultMetricsTest.json", true, true, null);
+    DimensionsAndCollector dimensionsAndCollector = metrics.getByName("query/time", "historical");
+    Assert.assertNotNull(dimensionsAndCollector);
+    String[] dimensions = dimensionsAndCollector.getDimensions();
+    Assert.assertEquals("dataSource", dimensions[0]);
+    Assert.assertEquals("druid_service", dimensions[1]);
+    Assert.assertEquals("host_name", dimensions[2]);
+    Assert.assertEquals("type", dimensions[3]);
+    Assert.assertEquals(1000.0, dimensionsAndCollector.getConversionFactor(), 0.0);
+    double[] expectedHistogramBuckets = {10.0, 30.0, 60.0, 120.0, 200.0, 300.0};
+    Assert.assertArrayEquals(expectedHistogramBuckets, dimensionsAndCollector.getHistogramBuckets(), 0.0);
+  }
+
 }

extensions-contrib/prometheus-emitter/src/test/resources/defaultInvalidMetricsTest.json

@@ -0,0 +1,3 @@
+{
+  "query/nonExistent" : { "dimensions" : ["dataSource"], "type" : "nonExistent", "help":  "Non supported type."}
+}

extensions-contrib/prometheus-emitter/src/test/resources/defaultMetricsTest.json

@@ -1,3 +1,3 @@
 {
-  "query/nonExistent" : { "dimensions" : ["dataSource"], "type" : "nonExistent", "help":  "Non supported type."}
-}
+  "query/time" : { "dimensions" : ["dataSource", "type"], "type" : "timer", "conversionFactor": 1000.0, "histogramBuckets": [10.0, 30.0, 60.0, 120.0, 200.0, 300.0], "help":  "Seconds taken to complete a query."}
+}