Class JvmMemoryPressure

java.lang.Object

com.kingsrook.qqq.backend.core.health.JvmMemoryPressure

public final class JvmMemoryPressure
extends Object

Tracks whether this JVM is under sustained memory pressure: the heap still full after garbage collection, or the JVM spending a large share of wall time in GC pauses. A JVM in that state answers every request slowly for minutes before it throws OutOfMemoryError, so probes use it to take the pod out of the load balancer (readiness) and, if it lasts, restart it (liveness). Readings are taken when a probe or the health runner asks (kubelet probes every few seconds); nothing runs in the background. Each reading compares against the oldest sample still inside the window: - heap after GC is the lowest after-GC occupancy seen in the window, so one full collection that frees the heap clears the condition; - GC time is the pause time added across the window divided by its length. Pressure starts when either crosses its threshold and ends only when the latest heap after GC is below the recovery percent and GC time is below its threshold, so a JVM near the line does not flap.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	JvmMemoryPressure.PlatformSource	Platform MXBeans: summed after-GC usage of heap pools, and pause time of collectors that stop the world.
static final record	JvmMemoryPressure.Reading	One evaluation.
static final record	JvmMemoryPressure.Settings	Thresholds, all from system properties or environment variables.
static interface	JvmMemoryPressure.Source	Where readings come from: the platform MXBeans, or a test double.

Constructor Summary

Constructors

Constructor	Description
JvmMemoryPressure(JvmMemoryPressure.Settings settings, JvmMemoryPressure.Source source, Clock clock)	Constructor (tests inject a source and clock).

Method Summary

Modifier and Type	Method	Description
static JvmMemoryPressure	get()	The JVM-wide monitor, configured from the environment on first use.
JvmMemoryPressure.Settings	getSettings()	Getter for settings
JvmMemoryPressure.Reading	sample()	Take a sample and evaluate the window.
static void	set(JvmMemoryPressure monitor)	Replace the JVM-wide monitor (tests); null re-reads the environment.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

JvmMemoryPressure

public JvmMemoryPressure(JvmMemoryPressure.Settings settings,
 JvmMemoryPressure.Source source,
 Clock clock)

Constructor (tests inject a source and clock).

Method Details

get

public static JvmMemoryPressure get()

The JVM-wide monitor, configured from the environment on first use.

set

public static void set(JvmMemoryPressure monitor)

Replace the JVM-wide monitor (tests); null re-reads the environment.

getSettings

public JvmMemoryPressure.Settings getSettings()

Getter for settings

sample

public JvmMemoryPressure.Reading sample()

Take a sample and evaluate the window.