Configure histogram flavor/max buckets per meter

docs/modules/ROOT/pages/implementations/otlp.adoc

@@ -146,14 +146,17 @@ Micrometer `Timer` and `DistributionSummary` support configuring xref:/concepts/
 | publishPercentiles and serviceLevelObjectives
 | Histogram
 |===
-__* The configuration `histogramFlavor` determines whether the OTLP DataPoint is a Histogram/Exponential Histogram.__
+__* The configuration `histogramFlavorPerMeter` and `histogramFlavor` determine whether the OTLP DataPoint is a Histogram/Exponential Histogram.__
 
-`OtlpMeterRegistry` supports 2 types of Histogram implementations (1.Explicit Bucket Histogram (or simply called Histogram), 2. Exponential Histogram) when `publishPercentileHistogram` is configured. The choice is chosen by setting `histogramFlavor` in `OtlpConfig` used by registry. When the implementation is exponential histogram, it also supports 2 additional properties
+`OtlpMeterRegistry` supports 2 types of Histogram implementations (1.Explicit Bucket Histogram (or simply called Histogram), 2. Exponential Histogram) when `publishPercentileHistogram` is configured.
+The type is determined by `histogramFlavorPerMeter` and `histogramFlavor` in `OtlpConfig` used by the registry.
+When the implementation is the exponential histogram, additional configuration applies:
 
-1. maxScale used to cap the maximum https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponential-scale[scale, window=_blank] used by the Exponential Histogram (defaults to 20).
-2. maxBuckets determines the maximum number of https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponential-buckets[buckets, window=_blank] to be used for exponential histograms (defaults to 160).
+1. `maxScale` used to cap the maximum https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponential-scale[scale, window=_blank] used by the Exponential Histogram (defaults to 20).
+2. `maxBuckets` determines the maximum number of https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponential-buckets[buckets, window=_blank] to be used for exponential histograms (defaults to 160).
+3. `maxBucketsPerMeter` overrides `maxBuckets` for specific meter names, giving more fine-grained configurability.
 
-Since Exponential Histogram cannot have custom SLO's specified, explicit bucket histogram is used whenever `serviceLevelObjectives` are added.
+Since Exponential Histogram cannot have custom SLO's specified, an explicit bucket histogram is used whenever `serviceLevelObjectives` are configured.
 
 ===  Configuration with Spring Boot
 If you use Spring Boot, you can use the https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#actuator.metrics.customizing.per-meter-properties[per-meter properties, window=_blank] to configure this behavior.

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpConfig.java

@@ -21,10 +21,7 @@
 
 import java.time.Duration;
 import java.net.URLDecoder;
-import java.util.Arrays;
-import java.util.Locale;
-import java.util.Map;
-import java.util.Objects;
+import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
@@ -215,6 +212,7 @@ default Map<String, String> headers() {
      * {@link HistogramFlavor#EXPLICIT_BUCKET_HISTOGRAM} is used for those meters.
      * </p>
      * @return - histogram flavor to be used
+     * @see #histogramFlavorPerMeter()
      *
      * @since 1.14.0
      */
@@ -229,6 +227,19 @@ default HistogramFlavor histogramFlavor() {
         });
     }
 
+    /**
+     * Configures the histogram flavor to use on a per-meter level. This will override the
+     * {@link #histogramFlavor()} configuration for matching Meters. The key is used to do
+     * an exact match on the Meter's name.
+     * @return mapping of meter name to histogram flavor
+     * @since 1.15.0
+     * @see #histogramFlavor()
+     */
+    default Map<String, HistogramFlavor> histogramFlavorPerMeter() {
+        return getStringMap(this, "histogramFlavorPerMeter", HistogramFlavor::fromString)
+            .orElse(Collections.emptyMap());
+    }
+
     /**
      * Max scale to use for exponential histograms, if configured.
      * @return maxScale
@@ -242,22 +253,39 @@ default int maxScale() {
 
     /**
      * Maximum number of buckets to be used for exponential histograms, if configured.
-     * This has no effect on explicit bucket histograms.
+     * This has no effect on explicit bucket histograms. This can be overridden per meter
+     * with {@link #maxBucketsPerMeter()}.
      * @return - maxBuckets
      * @see #histogramFlavor()
+     * @see #maxBucketsPerMeter()
      *
      * @since 1.14.0
      */
     default int maxBucketCount() {
         return getInteger(this, "maxBucketCount").orElse(160);
     }
 
+    /**
+     * Configures the max bucket count to use on a per-meter level. This will override the
+     * {@link #maxBucketCount()} configuration for matching Meters. The key is used to do
+     * an exact match on the Meter's name. This has no effect on a meter if it does not
+     * have an exponential bucket histogram configured.
+     * @return mapping of meter name to max bucket count
+     * @since 1.15.0
+     * @see #maxBucketCount()
+     */
+    default Map<String, Integer> maxBucketsPerMeter() {
+        return getStringMap(this, "maxBucketsPerMeter", Integer::parseInt).orElse(Collections.emptyMap());
+    }
+
     @Override
     default Validated<?> validate() {
         return checkAll(this, c -> PushRegistryConfig.validate(c), checkRequired("url", OtlpConfig::url),
                 check("resourceAttributes", OtlpConfig::resourceAttributes),
                 check("baseTimeUnit", OtlpConfig::baseTimeUnit),
-                check("aggregationTemporality", OtlpConfig::aggregationTemporality));
+                check("aggregationTemporality", OtlpConfig::aggregationTemporality),
+                check("histogramFlavorPerMeter", OtlpConfig::histogramFlavorPerMeter),
+                check("maxBucketsPerMeter", OtlpConfig::maxBucketsPerMeter));
     }
 
     default TimeUnit baseTimeUnit() {

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpCumulativeDistributionSummary.java

@@ -27,17 +27,12 @@
 class OtlpCumulativeDistributionSummary extends CumulativeDistributionSummary
         implements StartTimeAwareMeter, OtlpHistogramSupport {
 
-    private final HistogramFlavor histogramFlavor;
-
     private final long startTimeNanos;
 
     OtlpCumulativeDistributionSummary(Id id, Clock clock, DistributionStatisticConfig distributionStatisticConfig,
-            double scale, OtlpConfig otlpConfig) {
-        super(id, clock, distributionStatisticConfig, scale,
-                OtlpMeterRegistry.getHistogram(clock, distributionStatisticConfig, otlpConfig));
+            double scale, Histogram histogram) {
+        super(id, clock, distributionStatisticConfig, scale, histogram);
         this.startTimeNanos = TimeUnit.MILLISECONDS.toNanos(clock.wallTime());
-        this.histogramFlavor = OtlpMeterRegistry.histogramFlavor(otlpConfig.histogramFlavor(),
-                distributionStatisticConfig);
     }
 
     @Override
@@ -48,7 +43,7 @@ public long getStartTimeNanos() {
     @Override
     @Nullable
     public ExponentialHistogramSnapShot getExponentialHistogramSnapShot() {
-        if (histogramFlavor == HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM) {
+        if (histogram instanceof Base2ExponentialHistogram) {
             return ((Base2ExponentialHistogram) histogram).getLatestExponentialHistogramSnapshot();
         }
         return null;

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpCumulativeTimer.java

@@ -27,16 +27,11 @@
 
 class OtlpCumulativeTimer extends CumulativeTimer implements StartTimeAwareMeter, OtlpHistogramSupport {
 
-    private final HistogramFlavor histogramFlavor;
-
     private final long startTimeNanos;
 
     OtlpCumulativeTimer(Id id, Clock clock, DistributionStatisticConfig distributionStatisticConfig,
-            PauseDetector pauseDetector, TimeUnit baseTimeUnit, OtlpConfig otlpConfig) {
-        super(id, clock, distributionStatisticConfig, pauseDetector, baseTimeUnit,
-                OtlpMeterRegistry.getHistogram(clock, distributionStatisticConfig, otlpConfig, baseTimeUnit));
-        this.histogramFlavor = OtlpMeterRegistry.histogramFlavor(otlpConfig.histogramFlavor(),
-                distributionStatisticConfig);
+            PauseDetector pauseDetector, TimeUnit baseTimeUnit, Histogram histogram) {
+        super(id, clock, distributionStatisticConfig, pauseDetector, baseTimeUnit, histogram);
         this.startTimeNanos = TimeUnit.MILLISECONDS.toNanos(clock.wallTime());
     }
 
@@ -48,7 +43,7 @@ public long getStartTimeNanos() {
     @Override
     @Nullable
     public ExponentialHistogramSnapShot getExponentialHistogramSnapShot() {
-        if (histogramFlavor == HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM) {
+        if (histogram instanceof Base2ExponentialHistogram) {
             return ((Base2ExponentialHistogram) histogram).getLatestExponentialHistogramSnapshot();
         }
         return null;

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpMeterRegistry.java

@@ -205,16 +205,19 @@ protected Timer newTimer(Meter.Id id, DistributionStatisticConfig distributionSt
             PauseDetector pauseDetector) {
         return isCumulative()
                 ? new OtlpCumulativeTimer(id, this.clock, distributionStatisticConfig, pauseDetector, getBaseTimeUnit(),
-                        config)
-                : new OtlpStepTimer(id, clock, distributionStatisticConfig, pauseDetector, getBaseTimeUnit(), config);
+                        getHistogram(id, distributionStatisticConfig, getBaseTimeUnit()))
+                : new OtlpStepTimer(id, clock, pauseDetector,
+                        getHistogram(id, distributionStatisticConfig, getBaseTimeUnit()), config);
     }
 
     @Override
     protected DistributionSummary newDistributionSummary(Meter.Id id,
             DistributionStatisticConfig distributionStatisticConfig, double scale) {
         return isCumulative()
-                ? new OtlpCumulativeDistributionSummary(id, this.clock, distributionStatisticConfig, scale, config)
-                : new OtlpStepDistributionSummary(id, clock, distributionStatisticConfig, scale, config);
+                ? new OtlpCumulativeDistributionSummary(id, clock, distributionStatisticConfig, scale,
+                        getHistogram(id, distributionStatisticConfig))
+                : new OtlpStepDistributionSummary(id, clock, scale, getHistogram(id, distributionStatisticConfig),
+                        config);
     }
 
     @Override
@@ -372,13 +375,12 @@ Iterable<KeyValue> getResourceAttributes() {
         return attributes;
     }
 
-    static Histogram getHistogram(Clock clock, DistributionStatisticConfig distributionStatisticConfig,
-            OtlpConfig otlpConfig) {
-        return getHistogram(clock, distributionStatisticConfig, otlpConfig, null);
+    private Histogram getHistogram(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig) {
+        return getHistogram(id, distributionStatisticConfig, null);
     }
 
-    static Histogram getHistogram(final Clock clock, final DistributionStatisticConfig distributionStatisticConfig,
-            final OtlpConfig otlpConfig, @Nullable final TimeUnit baseTimeUnit) {
+    private Histogram getHistogram(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig,
+            @Nullable TimeUnit baseTimeUnit) {
         // While publishing to OTLP, we export either Histogram datapoint (Explicit
         // ExponentialBuckets
         // or Exponential) / Summary
@@ -387,21 +389,21 @@ static Histogram getHistogram(final Clock clock, final DistributionStatisticConf
         // exporting of histograms over percentiles is preferred in OTLP.
         if (distributionStatisticConfig.isPublishingHistogram()) {
             if (HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM
-                .equals(histogramFlavor(otlpConfig.histogramFlavor(), distributionStatisticConfig))) {
+                .equals(histogramFlavor(id, config, distributionStatisticConfig))) {
                 Double minimumExpectedValue = distributionStatisticConfig.getMinimumExpectedValueAsDouble();
                 if (minimumExpectedValue == null) {
                     minimumExpectedValue = 0.0;
                 }
 
-                return otlpConfig.aggregationTemporality() == AggregationTemporality.DELTA
-                        ? new DeltaBase2ExponentialHistogram(otlpConfig.maxScale(), otlpConfig.maxBucketCount(),
-                                minimumExpectedValue, baseTimeUnit, clock, otlpConfig.step().toMillis())
-                        : new CumulativeBase2ExponentialHistogram(otlpConfig.maxScale(), otlpConfig.maxBucketCount(),
+                return config.aggregationTemporality() == AggregationTemporality.DELTA
+                        ? new DeltaBase2ExponentialHistogram(config.maxScale(), getMaxBuckets(id), minimumExpectedValue,
+                                baseTimeUnit, clock, config.step().toMillis())
+                        : new CumulativeBase2ExponentialHistogram(config.maxScale(), getMaxBuckets(id),
                                 minimumExpectedValue, baseTimeUnit);
             }
 
             Histogram explicitBucketHistogram = getExplicitBucketHistogram(clock, distributionStatisticConfig,
-                    otlpConfig.aggregationTemporality(), otlpConfig.step().toMillis());
+                    config.aggregationTemporality(), config.step().toMillis());
             if (explicitBucketHistogram != null) {
                 return explicitBucketHistogram;
             }
@@ -413,8 +415,14 @@ static Histogram getHistogram(final Clock clock, final DistributionStatisticConf
         return NoopHistogram.INSTANCE;
     }
 
-    static HistogramFlavor histogramFlavor(HistogramFlavor preferredHistogramFlavor,
+    private int getMaxBuckets(Meter.Id id) {
+        return config.maxBucketsPerMeter().getOrDefault(id.getName(), config.maxBucketCount());
+    }
+
+    private HistogramFlavor histogramFlavor(Meter.Id id, OtlpConfig otlpConfig,
             DistributionStatisticConfig distributionStatisticConfig) {
+        HistogramFlavor preferredHistogramFlavor = otlpConfig.histogramFlavorPerMeter()
+            .getOrDefault(id.getName(), otlpConfig.histogramFlavor());
 
         final double[] serviceLevelObjectiveBoundaries = distributionStatisticConfig
             .getServiceLevelObjectiveBoundaries();

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpStepDistributionSummary.java

@@ -15,9 +15,10 @@
  */
 package io.micrometer.registry.otlp;
 
+import io.micrometer.common.lang.Nullable;
 import io.micrometer.core.instrument.AbstractDistributionSummary;
 import io.micrometer.core.instrument.Clock;
-import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
+import io.micrometer.core.instrument.distribution.Histogram;
 import io.micrometer.registry.otlp.internal.Base2ExponentialHistogram;
 import io.micrometer.registry.otlp.internal.ExponentialHistogramSnapShot;
 
@@ -26,8 +27,6 @@
 
 class OtlpStepDistributionSummary extends AbstractDistributionSummary implements OtlpHistogramSupport {
 
-    private final HistogramFlavor histogramFlavor;
-
     private final LongAdder count = new LongAdder();
 
     private final DoubleAdder total = new DoubleAdder();
@@ -40,18 +39,14 @@ class OtlpStepDistributionSummary extends AbstractDistributionSummary implements
      * Create a new {@code OtlpStepDistributionSummary}.
      * @param id ID
      * @param clock clock
-     * @param distributionStatisticConfig distribution statistic configuration
      * @param scale scale
      * @param otlpConfig config for registry
      */
-    OtlpStepDistributionSummary(Id id, Clock clock, DistributionStatisticConfig distributionStatisticConfig,
-            double scale, OtlpConfig otlpConfig) {
-        super(id, scale, OtlpMeterRegistry.getHistogram(clock, distributionStatisticConfig, otlpConfig));
+    OtlpStepDistributionSummary(Id id, Clock clock, double scale, Histogram histogram, OtlpConfig otlpConfig) {
+        super(id, scale, histogram);
         this.countTotal = new OtlpStepTuple2<>(clock, otlpConfig.step().toMillis(), 0L, 0.0, count::sumThenReset,
                 total::sumThenReset);
         this.max = new StepMax(clock, otlpConfig.step().toMillis());
-        this.histogramFlavor = OtlpMeterRegistry.histogramFlavor(otlpConfig.histogramFlavor(),
-                distributionStatisticConfig);
     }
 
     @Override
@@ -77,8 +72,9 @@ public double max() {
     }
 
     @Override
+    @Nullable
     public ExponentialHistogramSnapShot getExponentialHistogramSnapShot() {
-        if (histogramFlavor == HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM) {
+        if (histogram instanceof Base2ExponentialHistogram) {
             return ((Base2ExponentialHistogram) histogram).getLatestExponentialHistogramSnapshot();
         }
         return null;

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpStepTimer.java

@@ -15,9 +15,10 @@
  */
 package io.micrometer.registry.otlp;
 
+import io.micrometer.common.lang.Nullable;
 import io.micrometer.core.instrument.AbstractTimer;
 import io.micrometer.core.instrument.Clock;
-import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
+import io.micrometer.core.instrument.distribution.Histogram;
 import io.micrometer.core.instrument.distribution.pause.PauseDetector;
 import io.micrometer.core.instrument.util.TimeUtils;
 import io.micrometer.registry.otlp.internal.Base2ExponentialHistogram;
@@ -28,8 +29,6 @@
 
 class OtlpStepTimer extends AbstractTimer implements OtlpHistogramSupport {
 
-    private final HistogramFlavor histogramFlavor;
-
     private final LongAdder count = new LongAdder();
 
     private final LongAdder total = new LongAdder();
@@ -42,20 +41,14 @@ class OtlpStepTimer extends AbstractTimer implements OtlpHistogramSupport {
      * Create a new {@code OtlpStepTimer}.
      * @param id ID
      * @param clock clock
-     * @param distributionStatisticConfig distribution statistic configuration
      * @param pauseDetector pause detector
-     * @param baseTimeUnit base time unit
      * @param otlpConfig config of the registry
      */
-    OtlpStepTimer(Id id, Clock clock, DistributionStatisticConfig distributionStatisticConfig,
-            PauseDetector pauseDetector, TimeUnit baseTimeUnit, OtlpConfig otlpConfig) {
-        super(id, clock, pauseDetector, otlpConfig.baseTimeUnit(),
-                OtlpMeterRegistry.getHistogram(clock, distributionStatisticConfig, otlpConfig, baseTimeUnit));
+    OtlpStepTimer(Id id, Clock clock, PauseDetector pauseDetector, Histogram histogram, OtlpConfig otlpConfig) {
+        super(id, clock, pauseDetector, otlpConfig.baseTimeUnit(), histogram);
         countTotal = new OtlpStepTuple2<>(clock, otlpConfig.step().toMillis(), 0L, 0L, count::sumThenReset,
                 total::sumThenReset);
         max = new StepMax(clock, otlpConfig.step().toMillis());
-        this.histogramFlavor = OtlpMeterRegistry.histogramFlavor(otlpConfig.histogramFlavor(),
-                distributionStatisticConfig);
     }
 
     @Override
@@ -99,8 +92,9 @@ else if (histogram instanceof Base2ExponentialHistogram) {
     }
 
     @Override
+    @Nullable
     public ExponentialHistogramSnapShot getExponentialHistogramSnapShot() {
-        if (histogramFlavor == HistogramFlavor.BASE2_EXPONENTIAL_BUCKET_HISTOGRAM) {
+        if (histogram instanceof Base2ExponentialHistogram) {
             return ((Base2ExponentialHistogram) histogram).getLatestExponentialHistogramSnapshot();
         }
         return null;