From cb896ce8a75bf527972b1c4673f7c7ebf7367e73 Mon Sep 17 00:00:00 2001
From: Ken Wenzel <kenwenzel@gmx.net>
Date: Wed, 22 May 2024 11:41:48 +0200
Subject: [PATCH] Use moving sum for GC duration.

---
 .../rdf4j/sail/lmdb/MemoryOverflowModel.java  | 122 +++++++-----------
 1 file changed, 46 insertions(+), 76 deletions(-)

diff --git a/core/sail/lmdb/src/main/java/org/eclipse/rdf4j/sail/lmdb/MemoryOverflowModel.java b/core/sail/lmdb/src/main/java/org/eclipse/rdf4j/sail/lmdb/MemoryOverflowModel.java
index 0d74777f4c..38589c951b 100644
--- a/core/sail/lmdb/src/main/java/org/eclipse/rdf4j/sail/lmdb/MemoryOverflowModel.java
+++ b/core/sail/lmdb/src/main/java/org/eclipse/rdf4j/sail/lmdb/MemoryOverflowModel.java
@@ -26,6 +26,10 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import javax.management.NotificationEmitter;
+import javax.management.openmbean.CompositeData;
 
 import org.eclipse.rdf4j.common.io.FileUtil;
 import org.eclipse.rdf4j.model.IRI;
@@ -42,6 +46,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.sun.management.GarbageCollectionNotificationInfo;
+import com.sun.management.GcInfo;
+
 /**
  * Model implementation that stores in a {@link LinkedHashModel} until more than 10KB statements are added and the
  * estimated memory usage is more than the amount of free memory available. Once the threshold is cross this
@@ -75,6 +82,39 @@ abstract class MemoryOverflowModel extends AbstractModel implements AutoCloseabl
 
 	private final SimpleValueFactory vf = SimpleValueFactory.getInstance();
 
+	private static volatile boolean highGcLoad = false;
+	private static volatile long lastGcUpdate;
+	private static volatile long gcSum;
+	private static volatile List<GcInfo> gcInfos = new CopyOnWriteArrayList<>();
+	static {
+		List<GarbageCollectorMXBean> gcBeans = ManagementFactory.getGarbageCollectorMXBeans();
+		for (GarbageCollectorMXBean gcBean : gcBeans) {
+			NotificationEmitter emitter = (NotificationEmitter) gcBean;
+			emitter.addNotificationListener((notification, o) -> {
+				while (! gcInfos.isEmpty()) {
+					if (System.currentTimeMillis() - gcInfos.get(0).getEndTime() > 5000) {
+						gcSum -= gcInfos.remove(0).getDuration();
+					} else {
+						break;
+					}
+				}
+
+				// extract garbage collection information from notification.
+				GarbageCollectionNotificationInfo gcNotificationInfo = GarbageCollectionNotificationInfo.from((CompositeData) notification.getUserData());
+				GcInfo gcInfo = gcNotificationInfo.getGcInfo();
+				gcInfos.add(gcInfo);
+				gcSum += gcInfo.getDuration();
+				System.out.println("gcSum: " + gcSum);
+				if (gcSum > 1000) {
+					highGcLoad = true;
+					lastGcUpdate = System.currentTimeMillis();
+				} else if (System.currentTimeMillis() - lastGcUpdate > 10000) {
+					highGcLoad = false;
+				}
+			}, null, null);
+		}
+	}
+
 	public MemoryOverflowModel(boolean verifyAdditions) {
 		this.verifyAdditions = verifyAdditions;
 		memory = new LinkedHashModel(LARGE_BLOCK);
@@ -148,7 +188,7 @@ public boolean addAll(Collection<? extends Statement> c) {
 				if (buffer.size() >= 1024) {
 					ret |= getDelegate().addAll(buffer);
 					buffer.clear();
-					innerCheckMemoryOverflow();
+					checkMemoryOverflow();
 				}
 			}
 			if (!buffer.isEmpty()) {
@@ -266,85 +306,15 @@ private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundEx
 		}
 	}
 
-	static class GcInfo {
-		long count;
-		long time;
-	}
-
-	private final Map<String, GcInfo> prevGcInfo = new ConcurrentHashMap<>();
-
-	private synchronized boolean highGcLoad() {
-		boolean highLoad = false;
-
-		// get all garbage collector MXBeans.
-		List<GarbageCollectorMXBean> gcBeans = ManagementFactory.getGarbageCollectorMXBeans();
-		for (GarbageCollectorMXBean gcBean : gcBeans) {
-			long count = gcBean.getCollectionCount();
-			long time = gcBean.getCollectionTime();
-
-			GcInfo prevInfo = prevGcInfo.get(gcBean.getName());
-			if (prevInfo != null) {
-				long countDiff = count - prevInfo.count;
-				long timeDiff = time - prevInfo.time;
-				if (countDiff != 0) {
-					double gcLoad = (double) timeDiff / countDiff;
-					// TODO find good threshold
-					if (gcLoad > 100) {
-						highLoad = true;
-					}
-				}
-			} else {
-				prevInfo = new GcInfo();
-				prevGcInfo.put(gcBean.getName(), prevInfo);
-			}
-			prevInfo.count = count;
-			prevInfo.time = time;
-		}
-		return highLoad;
-	}
-
-	private void checkMemoryOverflow() {
+	private synchronized void checkMemoryOverflow() {
 		if (disk == getDelegate()) {
 			return;
 		}
 
-		if (overflow) {
-			innerCheckMemoryOverflow();
-		}
-		int size = size() + 1;
-		if (size >= LARGE_BLOCK && size % LARGE_BLOCK == 0) {
-			if (highGcLoad()) {
-				logger.debug("syncing at {} triples due to high gc load.", size);
-				overflowToDisk();
-			} else {
-				innerCheckMemoryOverflow();
-			}
-		}
-	}
-
-	private synchronized void innerCheckMemoryOverflow() {
-		if (disk == null) {
-			// maximum heap size the JVM can allocate
-			long maxMemory = RUNTIME.maxMemory();
-
-			// total currently allocated JVM memory
-			long totalMemory = RUNTIME.totalMemory();
-
-			// amount of memory free in the currently allocated JVM memory
-			long freeMemory = RUNTIME.freeMemory();
-
-			// estimated memory used
-			long used = totalMemory - freeMemory;
-
-			// amount of memory the JVM can still allocate from the OS (upper boundary is the max heap)
-			long freeToAllocateMemory = maxMemory - used;
-
-			// try to prevent OOM
-			overflow = freeToAllocateMemory < MIN_AVAILABLE_MEM_BEFORE_OVERFLOWING;
-			if (overflow) {
-				logger.debug("syncing at {} triples.", size());
-				overflowToDisk();
-			}
+		if (highGcLoad) {
+			logger.debug("syncing at {} triples due to gc load");
+			overflowToDisk();
+			System.gc();
 		}
 	}