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Add Gauges for memory usage after GC #7296

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Add Gauges for memory usage after GC #7296

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61fe1a5
Add Gauges for memory usage after GC
shakuzen Mar 16, 2026
d92c05b
Use `@GcTest`
shakuzen Mar 16, 2026
1c13a13
Update jvm.memory.usage.after.gc description as deprecated
shakuzen Mar 19, 2026
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14 changes: 14 additions & 0 deletions micrometer-core/src/main/java/io/micrometer/core/instrument/binder/jvm/JvmMemoryMetrics.java
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Expand Up @@ -120,6 +120,20 @@ public void bindTo(MeterRegistry registry) {
.description("The maximum amount of memory in bytes that can be used for memory management")
.baseUnit(BaseUnits.BYTES)
.register(registry);

JvmMemoryMeterConventions.JvmMemoryUsedAfterLastGcConvention memoryUsedAfterLastGcConvention = conventions
.getMemoryUsedAfterLastGcConvention();
if (memoryPoolBean.getCollectionUsage() != null) {
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@shakuzen shakuzen Mar 16, 2026

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I did have a version of this code that registered pools even if this returns null, but they always have the value NaN which didn't seem worthwhile registering.

Gauge.builder(memoryUsedAfterLastGcConvention.getName(), memoryPoolBean, pool -> {
MemoryUsage collectionUsage = pool.getCollectionUsage();
return collectionUsage != null ? collectionUsage.getUsed() : Double.NaN;
})
.tags(memoryUsedAfterLastGcConvention.getTags(memoryPoolBean))
.description(
"Measure of memory used, as measured after the most recent garbage collection event on this pool.")
.baseUnit(BaseUnits.BYTES)
.register(registry);
}
}
}

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30 changes: 30 additions & 0 deletions ...n/java/io/micrometer/core/instrument/binder/jvm/convention/JvmMemoryMeterConventions.java
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Expand Up @@ -15,6 +15,7 @@
*/
package io.micrometer.core.instrument.binder.jvm.convention;

import io.micrometer.core.instrument.Tags;
import io.micrometer.core.instrument.binder.MeterConvention;

import java.lang.management.MemoryPoolMXBean;
Expand All @@ -33,4 +34,33 @@ public interface JvmMemoryMeterConventions {

MeterConvention<MemoryPoolMXBean> getMemoryMaxConvention();

/**
* Convention for JVM memory used after last GC.
* @return convention for JVM memory used after last GC
* @since 1.17.0
*/
default JvmMemoryUsedAfterLastGcConvention getMemoryUsedAfterLastGcConvention() {
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@shakuzen shakuzen Mar 16, 2026

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While other methods here have return type MeterConvention<MemoryPoolMXBean>, that was probably a mistake that I tried to not repeat here. In a framework's configuration model, it would be reasonable for there to be a way for a user to provide a custom convention for a specific convention, and that's made harder by using generic types that do not uniquely identify a single convention.

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@jonatan-ivanov jonatan-ivanov Mar 16, 2026

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Should we create an issue for 2.x?

return new JvmMemoryUsedAfterLastGcConvention() {
};
}

/**
* {@link MeterConvention} for JVM memory used after last GC.
*
* @since 1.17.0
*/
interface JvmMemoryUsedAfterLastGcConvention extends MeterConvention<MemoryPoolMXBean> {
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@shakuzen shakuzen Mar 16, 2026 •
edited
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I don't know if it would be better to make this a top level type - it can be a bit annoying to reference it as JvmMemoryMeterConventions.JvmMemoryUsedAfterLastGcConvention, but maybe it also logically groups what would be the individual convention types (if we had them for the other conventions here, that is).

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@jonatan-ivanov jonatan-ivanov Mar 16, 2026

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Grouping makes sense to me. Not sure how well-known it is but if people annoyed by using JvmMemoryMeterConventions.JvmMemoryUsedAfterLastGcConvention, they can static import it:

import static io.micrometer.core.instrument.binder.jvm.convention.JvmMemoryMeterConventions.JvmMemoryUsedAfterLastGcConvention;

and use only JvmMemoryUsedAfterLastGcConvention like it would be a top-level type.


@Override
default String getName() {
return "jvm.memory.used_after_last_gc";
}

@Override
default Tags getTags(MemoryPoolMXBean memoryPoolBean) {
return Tags.empty();
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@shakuzen shakuzen Mar 16, 2026

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The default implementation is not useful, but it was needed since we can't add a new non-default method to the JvmMemoryMeterConventions interface without breaking types that extend/implement it.

}

}

}
11 changes: 11 additions & 0 deletions ...core/instrument/binder/jvm/convention/micrometer/MicrometerJvmMemoryMeterConventions.java
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Expand Up @@ -61,4 +61,15 @@ public MeterConvention<MemoryPoolMXBean> getMemoryMaxConvention() {
return new SimpleMeterConvention<>("jvm.memory.max", this::getCommonTags);
}

@Override
public JvmMemoryUsedAfterLastGcConvention getMemoryUsedAfterLastGcConvention() {
return new JvmMemoryUsedAfterLastGcConvention() {

@Override
public Tags getTags(MemoryPoolMXBean memoryPoolBean) {
return getCommonTags(memoryPoolBean);
}
};
}

}
18 changes: 18 additions & 0 deletions ...ter-core/src/test/java/io/micrometer/core/instrument/binder/jvm/JvmMemoryMetricsTest.java
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Expand Up @@ -30,6 +30,7 @@
*
* @author Michael Weirauch
*/
@GcTest
class JvmMemoryMetricsTest {

MeterRegistry registry = new SimpleMeterRegistry();
Expand Down Expand Up @@ -81,6 +82,23 @@ void otelMemoryMetricsWithExtraTags() {
assertJvmMemoryMetrics("non_heap", extraTags, true);
}

@Test
void memoryUsedAfterLastGc() {
new JvmMemoryMetrics().bindTo(registry);

assertThat(registry.get("jvm.memory.used_after_last_gc").gauges()).isNotEmpty()
.allSatisfy(gauge -> assertThat(gauge.value()).isGreaterThanOrEqualTo(0));

System.gc();

assertThat(registry.get("jvm.memory.used_after_last_gc").gauges()).isNotEmpty()
.allSatisfy(gauge -> assertThat(gauge.value()).isGreaterThanOrEqualTo(0));

registry.get("jvm.memory.used_after_last_gc").gauges().forEach(gauge -> {
assertThat(gauge.getId().getBaseUnit()).isEqualTo(BaseUnits.BYTES);
});
}

private void assertJvmMemoryMetrics(String area) {
assertJvmMemoryMetrics(area, Tags.empty());
}
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