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Merged
juha-aiven merged 1 commit into from
Jan 22, 2026
Merged

fix(storage:metrics): eagerly initialize meters with only topicType tag #493

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16 changes: 10 additions & 6 deletions storage/src/main/java/org/apache/kafka/storage/log/metrics/BrokerTopicMetrics.java
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Original file line number Diff line number Diff line change
Expand Up @@ -90,14 +90,12 @@ private BrokerTopicMetrics(Optional<String> name, boolean remoteStorageEnabled)
final MeterWrapper classicBytesInRate;
final MeterWrapper classicBytesOutRate;
if (isAllTopicsStats) {
// All-topics (broker-level) meters with topicType tag are eagerly initialized
// by MeterWrapper constructor since they only have topicType tag (global metrics).
classicBytesInRate = new MeterWrapper(BYTES_IN_PER_SEC, "bytes", classicTags);
classicBytesOutRate = new MeterWrapper(BYTES_OUT_PER_SEC, "bytes", classicTags);
disklessBytesInRate = new MeterWrapper(BYTES_IN_PER_SEC, "bytes", disklessTags);
disklessBytesOutRate = new MeterWrapper(BYTES_OUT_PER_SEC, "bytes", disklessTags);

// Keep broker-level behavior: eagerly initialize the classic meters.
classicBytesInRate.meter();
classicBytesOutRate.meter();
} else {
classicBytesInRate = new MeterWrapper(BYTES_IN_PER_SEC, "bytes", tags);
classicBytesOutRate = new MeterWrapper(BYTES_OUT_PER_SEC, "bytes", tags);
Expand Down Expand Up @@ -486,8 +484,14 @@ public MeterWrapper(String metricType, String eventType, Map<String, String> met
this.metricType = metricType;
this.eventType = eventType;
this.metricTags = new HashMap<>(metricTags);
if (this.metricTags.isEmpty()) {
meter(); // greedily initialize the general topic metrics
// Eagerly initialize global metrics so they are always registered and visible in monitoring
// systems from broker startup, even before any traffic is recorded.
// Global metrics are those with:
// - No tags (general broker-level metrics)
// - Only topicType tag (broker-level metrics split by topic type, e.g., classic vs diskless)
boolean onlyTopicTypeTag = this.metricTags.size() == 1 && this.metricTags.containsKey("topicType");
if (this.metricTags.isEmpty() || onlyTopicTypeTag) {
meter();
}
}

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125 changes: 125 additions & 0 deletions storage/src/test/java/org/apache/kafka/storage/log/metrics/BrokerTopicMetricsTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,8 @@
*/
package org.apache.kafka.storage.log.metrics;

import org.apache.kafka.server.metrics.KafkaYammerMetrics;

import com.yammer.metrics.core.Meter;

import org.junit.jupiter.api.AfterEach;
Expand All @@ -39,6 +41,7 @@
import static org.junit.jupiter.api.Assertions.assertNotEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNotSame;
import static org.junit.jupiter.api.Assertions.assertSame;
import static org.junit.jupiter.api.Assertions.assertTrue;

/**
Expand Down Expand Up @@ -176,6 +179,128 @@ public void testDefaultMethodsUseClassicTopicType() {
"Default bytesOutRate() should return same meter as bytesOutRate(false) for all-topics stats");
}

/**
* Verifies that all-topics (broker-level) meters are eagerly initialized during construction.
* This includes:
* - Meters with no tags (general broker metrics)
* - Meters with only topicType tag (classic and diskless variants for bytesIn/bytesOut)
*
* Eager initialization is required so these global metrics are always registered and visible
* in monitoring systems from broker startup, even before any traffic is recorded.
*
* This test ensures that the eager initialization logic cannot be accidentally removed
* without breaking tests (regression prevention for issue introduced in aa045fbd).
*/
@Test
public void testAllTopicsMetersAreEagerlyInitialized() {
// Create a fresh instance to verify eager initialization happens during construction
BrokerTopicMetrics freshAllTopicsStats = new BrokerTopicMetrics(false);

try {
// For all-topics stats, both classic and diskless meters should be eagerly initialized.
// We verify this by checking that calling meter() multiple times returns the SAME instance,
// which proves the meter was already created (not lazily created on first access).

// Classic meters (topicType=classic) should be eagerly initialized
Meter classicBytesIn1 = freshAllTopicsStats.bytesInRate(false);
Meter classicBytesIn2 = freshAllTopicsStats.bytesInRate(false);
assertSame(classicBytesIn1, classicBytesIn2,
"Classic bytesInRate should return same instance (eagerly initialized)");

Meter classicBytesOut1 = freshAllTopicsStats.bytesOutRate(false);
Meter classicBytesOut2 = freshAllTopicsStats.bytesOutRate(false);
assertSame(classicBytesOut1, classicBytesOut2,
"Classic bytesOutRate should return same instance (eagerly initialized)");

// Diskless meters (topicType=diskless) should also be eagerly initialized
// This is the regression that was introduced in aa045fbd - the diskless meters
// with only topicType tag were not being eagerly initialized
Meter disklessBytesIn1 = freshAllTopicsStats.bytesInRate(true);
Meter disklessBytesIn2 = freshAllTopicsStats.bytesInRate(true);
assertSame(disklessBytesIn1, disklessBytesIn2,
"Diskless bytesInRate should return same instance (eagerly initialized)");

Meter disklessBytesOut1 = freshAllTopicsStats.bytesOutRate(true);
Meter disklessBytesOut2 = freshAllTopicsStats.bytesOutRate(true);
assertSame(disklessBytesOut1, disklessBytesOut2,
"Diskless bytesOutRate should return same instance (eagerly initialized)");

// Also verify that general metrics (no tags) are eagerly initialized
Meter messagesIn1 = freshAllTopicsStats.messagesInRate();
Meter messagesIn2 = freshAllTopicsStats.messagesInRate();
assertSame(messagesIn1, messagesIn2,
"messagesInRate should return same instance (eagerly initialized for all-topics stats)");
} finally {
freshAllTopicsStats.close();
}
}

/**
* Verifies that all-topics (broker-level) meters with topicType tag are registered in the
* metrics registry immediately upon construction, without requiring any explicit access.
*
* This is a stronger test than testAllTopicsMetersAreEagerlyInitialized - it verifies that
* the metrics are actually present in the Yammer registry right after construction, which
* ensures they will be visible in monitoring systems from broker startup.
*
* This test specifically guards against the regression in aa045fbd where the eager
* initialization logic for metrics with only topicType tag was accidentally removed.
*/
@Test
public void testAllTopicsMetersWithTopicTypeTagAreRegisteredOnConstruction() {
// First, verify no metrics with our specific tags exist before construction
// (they might exist from other tests, so we'll just check they exist after)

// Create a fresh instance - this should eagerly register the metrics
BrokerTopicMetrics freshAllTopicsStats = new BrokerTopicMetrics(false);

try {
// Check that the classic bytesIn/bytesOut meters (topicType=classic) are registered
assertTrue(isMetricRegistered("BytesInPerSec", "topicType", "classic"),
"BytesInPerSec with topicType=classic should be registered immediately on construction");
assertTrue(isMetricRegistered("BytesOutPerSec", "topicType", "classic"),
"BytesOutPerSec with topicType=classic should be registered immediately on construction");

// Check that the diskless bytesIn/bytesOut meters (topicType=diskless) are registered
// This is the key assertion - these were not being eagerly initialized after aa045fbd
assertTrue(isMetricRegistered("BytesInPerSec", "topicType", "diskless"),
"BytesInPerSec with topicType=diskless should be registered immediately on construction " +
"(regression check for aa045fbd - metrics with only topicType tag must be eagerly initialized)");
assertTrue(isMetricRegistered("BytesOutPerSec", "topicType", "diskless"),
"BytesOutPerSec with topicType=diskless should be registered immediately on construction " +
"(regression check for aa045fbd - metrics with only topicType tag must be eagerly initialized)");
} finally {
freshAllTopicsStats.close();
}
}

/**
* Helper method to check if a metric with given name and tag is registered in the Yammer registry.
*/
private boolean isMetricRegistered(String metricName, String tagKey, String tagValue) {
return KafkaYammerMetrics.defaultRegistry().allMetrics().keySet().stream()
.anyMatch(mn -> mn.getName().equals(metricName)
&& mn.getScope() != null
&& mn.getScope().contains(tagKey + "." + tagValue));
}

/**
* Verifies that topic-specific meters are lazily initialized (only created on first access).
* This is different from all-topics stats because we don't want to create meters for topics
* that may never be accessed.
*/
@Test
public void testTopicSpecificMetersAreLazilyInitialized() {
// For topic-specific stats, meters are created lazily when first accessed.
// We can't directly test "not initialized" without internal access, but we can verify
// that the meter IS created when accessed and remains the same instance.

Meter bytesIn1 = topicSpecificStats.bytesInRate();
Meter bytesIn2 = topicSpecificStats.bytesInRate();
assertSame(bytesIn1, bytesIn2,
"Topic-specific bytesInRate should return same instance after first access");
}

@Test
public void testMultipleTopicSpecificMetricsAreDistinct() {
// Different topics should have different meters (different topic name tags)
Expand Down
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