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new 46ad599a6ef MINOR: Add toString() to KafkaMetric for readable logging
(#22129)
46ad599a6ef is described below
commit 46ad599a6ef15c6a5f6296cb574ad25a1b7836eb
Author: Aditya Kousik <[email protected]>
AuthorDate: Mon Jun 1 02:01:35 2026 -0700
MINOR: Add toString() to KafkaMetric for readable logging (#22129)
This adds a toString() that includes the metric name, group,
description, and tags. The metricValueProvider is represented by its
simple class name rather than its full toString() to avoid dumping
internal stat state like SampledStat's samples list into logs
Reviewers: Apoorv Mittal <[email protected]>
---
.../apache/kafka/common/metrics/KafkaMetric.java | 20 ++++++
.../kafka/common/metrics/KafkaMetricTest.java | 74 ++++++++++++++++++++--
2 files changed, 87 insertions(+), 7 deletions(-)
diff --git
a/clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java
b/clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java
index a9203ead0a0..3834c870603 100644
--- a/clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java
+++ b/clients/src/main/java/org/apache/kafka/common/metrics/KafkaMetric.java
@@ -124,4 +124,24 @@ public final class KafkaMetric implements Metric {
this.config = config;
}
}
+
+ /**
+ * Returns a human-readable representation of this metric.
+ *
+ * <p>The metricValueProvider is represented by its class name rather than
its full
+ * toString() to avoid dumping internal stat state (e.g. SampledStat's
samples list) into
+ * logs, which could be verbose and is rarely useful for identifying which
metric changed.
+ */
+ @Override
+ public String toString() {
+ Class<?> cls = metricValueProvider.getClass();
+ if (cls.isSynthetic() || cls.isAnonymousClass()) {
+ return "KafkaMetric [metricName=" + metricName + "]";
+ }
+
+ return "KafkaMetric [" +
+ "metricName=" + metricName +
+ ", metricValueProvider=" +
metricValueProvider.getClass().getName() +
+ ']';
+ }
}
diff --git
a/clients/src/test/java/org/apache/kafka/common/metrics/KafkaMetricTest.java
b/clients/src/test/java/org/apache/kafka/common/metrics/KafkaMetricTest.java
index e3a9fb345d7..b5b543c006c 100644
--- a/clients/src/test/java/org/apache/kafka/common/metrics/KafkaMetricTest.java
+++ b/clients/src/test/java/org/apache/kafka/common/metrics/KafkaMetricTest.java
@@ -17,11 +17,12 @@
package org.apache.kafka.common.metrics;
import org.apache.kafka.common.MetricName;
+import org.apache.kafka.common.metrics.stats.Avg;
import org.apache.kafka.common.utils.MockTime;
import org.junit.jupiter.api.Test;
-import java.util.Collections;
+import java.util.Map;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -30,12 +31,18 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
public class KafkaMetricTest {
- private static final MetricName METRIC_NAME = new MetricName("name",
"group", "description", Collections.emptyMap());
+ private static final MetricName METRIC_NAME_1 = new MetricName("name",
"group", "description", Map.of());
+ private static final MetricName METRIC_NAME_2 = new MetricName(
+ "request-latency-avg",
+ "consumer-fetch-manager-metrics",
+ "The average request latency in ms",
+ Map.of("client-id", "consumer-1")
+ );
@Test
public void testIsMeasurable() {
Measurable metricValueProvider = (config, now) -> 0;
- KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME,
metricValueProvider, new MetricConfig(), new MockTime());
+ KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME_1,
metricValueProvider, new MetricConfig(), new MockTime());
assertTrue(metric.isMeasurable());
assertEquals(metricValueProvider, metric.measurable());
}
@@ -43,7 +50,7 @@ public class KafkaMetricTest {
@Test
public void testIsMeasurableWithGaugeProvider() {
Gauge<Double> metricValueProvider = (config, now) -> 0.0;
- KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME,
metricValueProvider, new MetricConfig(), new MockTime());
+ KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME_1,
metricValueProvider, new MetricConfig(), new MockTime());
assertFalse(metric.isMeasurable());
assertThrows(IllegalStateException.class, metric::measurable);
}
@@ -54,14 +61,14 @@ public class KafkaMetricTest {
MetricConfig config = new MetricConfig();
Gauge<Integer> gauge = (c, now) -> 7;
- KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME, gauge,
config, time);
+ KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME_1,
gauge, config, time);
assertEquals(0.0d, metric.measurableValue(time.milliseconds()), 0.0d);
}
@Test
public void testKafkaMetricAcceptsNonMeasurableNonGaugeProvider() {
MetricValueProvider<String> provider = (config, now) -> "metric value
provider";
- KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME,
provider, new MetricConfig(), new MockTime());
+ KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME_1,
provider, new MetricConfig(), new MockTime());
Object value = metric.metricValue();
assertEquals("metric value provider", value);
@@ -70,7 +77,60 @@ public class KafkaMetricTest {
@Test
public void testConstructorWithNullProvider() {
assertThrows(NullPointerException.class, () ->
- new KafkaMetric(new Object(), METRIC_NAME, null, new
MetricConfig(), new MockTime())
+ new KafkaMetric(new Object(), METRIC_NAME_1, null, new
MetricConfig(), new MockTime())
);
}
+
+ /**
+ * Verifies that toString produces a human-readable representation
suitable for logging.
+ * Note that we skip the metric provider in this case, but this is still a
+ * significant improvement over the default Object.toString() output (e.g.
"KafkaMetric@62a7d6c6").
+ */
+ @Test
+ public void testToStringWithLambdaProvider() {
+ Measurable metricValueProvider = (config, now) -> 0;
+ testToStringOnLambdaOrAnonymousClass(metricValueProvider);
+ }
+
+ /**
+ * Verifies that toString produces a human-readable representation
suitable for logging.
+ * Note that we skip the metric provider in this case, but this is still a
+ * significant improvement over the default Object.toString() output (e.g.
"KafkaMetric@62a7d6c6").
+ */
+ @Test
+ public void testToStringWithAnonymousClassProvider() {
+ //noinspection Convert2Lambda
+ Measurable metricValueProvider = new Measurable() {
+ @Override
+ public double measure(MetricConfig config, long now) {
+ return 0;
+ }
+ };
+ testToStringOnLambdaOrAnonymousClass(metricValueProvider);
+ }
+
+ @Test
+ public void testToStringWithStatProvider() {
+ Avg avg = new Avg();
+ KafkaMetric metric = new KafkaMetric(new Object(), METRIC_NAME_2, avg,
new MetricConfig(), new MockTime());
+
+ assertEquals("KafkaMetric [metricName=MetricName
[name=request-latency-avg, "
+ + "group=consumer-fetch-manager-metrics, "
+ + "description=The average request latency in ms, "
+ + "tags={client-id=consumer-1}], "
+ +
"metricValueProvider=org.apache.kafka.common.metrics.stats.Avg]",
+ metric.toString());
+ }
+
+ private void testToStringOnLambdaOrAnonymousClass(Measurable
metricValueProvider) {
+ KafkaMetric metric = new KafkaMetric(
+ new Object(), METRIC_NAME_2, metricValueProvider, new
MetricConfig(), new MockTime());
+
+ String result = metric.toString();
+ assertEquals("KafkaMetric [metricName=MetricName
[name=request-latency-avg, "
+ + "group=consumer-fetch-manager-metrics, "
+ + "description=The average request latency in ms, "
+ + "tags={client-id=consumer-1}]]",
+ result);
+ }
}
