diff --git a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexUpdateTests.java b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexUpdateTests.java
index a3c181ba329..30fbea48661 100644
--- a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexUpdateTests.java
+++ b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexUpdateTests.java
@@ -96,7 +96,7 @@ public class IndexUpdateTests extends IndexTestBase {
 			fContentUsed= -1;
 		}
 		IProject project= cpp ? fCppProject.getProject() : fCProject.getProject();
-		fFile= TestSourceReader.createFile(project, "header.h", fContents[++fContentUsed].toString());
+		fHeader= TestSourceReader.createFile(project, "header.h", fContents[++fContentUsed].toString());
 		assertTrue(CCorePlugin.getIndexManager().joinIndexer(INDEXER_WAIT_TIME, NPM));
 	}
 
@@ -711,4 +711,49 @@ public class IndexUpdateTests extends IndexTestBase {
 		}
 	}
 
+	// int globalVar;
+	
+	// #include "header.h"
+	// void test() {
+	//    globalVar= 1;
+	// }
+	public void testChangingSourceBeforeHeader_Bug171834() throws Exception {
+		setupHeader(2, true);
+		setupFile(0, true);
+		IBinding binding;
+		ICompositeType ct;
+		fIndex.acquireReadLock();
+		try {
+			binding = findBinding("globalVar");
+			assertTrue(binding instanceof IVariable);
+			assertEquals(2, fIndex.findNames(binding, IIndex.FIND_ALL_OCCURENCES).length);
+		} finally {
+			fIndex.releaseReadLock();
+		}
+
+		fFile= TestSourceReader.createFile(fFile.getParent(), fFile.getName(), fContents[1].toString().replaceAll("globalVar", "newVar"));
+		TestSourceReader.waitUntilFileIsIndexed(fIndex, fFile, INDEXER_WAIT_TIME);
+		
+		fIndex.acquireReadLock();
+		try {
+			binding = findBinding("globalVar");
+			assertTrue(binding instanceof IVariable);
+			assertEquals(1, fIndex.findNames(binding, IIndex.FIND_ALL_OCCURENCES).length);
+		} finally {
+			fIndex.releaseReadLock();
+		}
+
+		fHeader= TestSourceReader.createFile(fHeader.getParent(), fHeader.getName(), fContents[0].toString().replaceAll("globalVar", "newVar"));
+		TestSourceReader.waitUntilFileIsIndexed(fIndex, fHeader, INDEXER_WAIT_TIME);
+		assertTrue(CCorePlugin.getIndexManager().joinIndexer(INDEXER_WAIT_TIME, NPM));
+
+		fIndex.acquireReadLock();
+		try {
+			binding = findBinding("newVar");
+			assertTrue(binding instanceof IVariable);
+			assertEquals(2, fIndex.findNames(binding, IIndex.FIND_ALL_OCCURENCES).length);
+		} finally {
+			fIndex.releaseReadLock();
+		}
+	}
 }
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/CModelListener.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/CModelListener.java
index c1bfe1cef94..9ffa2eea084 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/CModelListener.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/CModelListener.java
@@ -11,12 +11,22 @@
 
 package org.eclipse.cdt.internal.core.pdom;
 
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
 import org.eclipse.cdt.core.CCorePlugin;
+import org.eclipse.cdt.core.dom.IPDOMIndexer;
+import org.eclipse.cdt.core.dom.IPDOMManager;
 import org.eclipse.cdt.core.model.ElementChangedEvent;
 import org.eclipse.cdt.core.model.ICElement;
 import org.eclipse.cdt.core.model.ICElementDelta;
 import org.eclipse.cdt.core.model.ICProject;
 import org.eclipse.cdt.core.model.IElementChangedListener;
+import org.eclipse.cdt.core.model.ITranslationUnit;
+import org.eclipse.cdt.internal.core.pdom.indexer.DeltaAnalyzer;
 import org.eclipse.core.resources.IResourceChangeEvent;
 import org.eclipse.core.resources.IResourceChangeListener;
 import org.eclipse.core.runtime.CoreException;
@@ -26,8 +36,14 @@ import org.eclipse.core.runtime.CoreException;
  * @since 4.0
  */
 public class CModelListener implements IElementChangedListener, IResourceChangeListener {
+	private static final int UPDATE_LR_CHANGED_FILES_COUNT = 5;
 
 	private PDOMManager fManager;
+	private LinkedHashMap fLRUs= new LinkedHashMap(UPDATE_LR_CHANGED_FILES_COUNT, 0.75f, true) {
+		protected boolean removeEldestEntry(Map.Entry eldest) {
+			return size() > UPDATE_LR_CHANGED_FILES_COUNT;
+		}
+	};
 
 	public CModelListener(PDOMManager manager) {
 		fManager= manager;
@@ -38,22 +54,30 @@ public class CModelListener implements IElementChangedListener, IResourceChangeL
 		if (event.getType() != ElementChangedEvent.POST_CHANGE)
 			return;
 		
-		// Walk the delta sending the subtrees to the appropriate indexers
-		try { 
-			processDelta(event.getDelta());
-		} catch (CoreException e) {
-			CCorePlugin.log(e);
+		// Walk the delta collecting tu's per project
+		HashMap changeMap= new HashMap();
+		processDelta(event.getDelta(), changeMap);
+		
+		// bug 171834 update last recently changed sources
+		addLastRecentlyUsed(changeMap);
+				
+		for (Iterator it = changeMap.entrySet().iterator(); it.hasNext();) {
+			Map.Entry entry = (Map.Entry) it.next();
+			ICProject cproject = (ICProject) entry.getKey();
+			DeltaAnalyzer analyzer= (DeltaAnalyzer) entry.getValue();
+			fManager.changeProject(cproject, analyzer.getAddedTUs(), analyzer.getChangedTUs(), analyzer.getRemovedTUs());
 		}
 	}
 	
-	private void processDelta(ICElementDelta delta) throws CoreException {
+	private void processDelta(ICElementDelta delta, HashMap changeMap) {
 		int type = delta.getElement().getElementType();
 		switch (type) {
 		case ICElement.C_MODEL:
 			// Loop through the children
 			ICElementDelta[] children = delta.getAffectedChildren();
-			for (int i = 0; i < children.length; ++i)
-				processDelta(children[i]);
+			for (int i = 0; i < children.length; ++i) {
+				processDelta(children[i], changeMap);
+			}
 			break;
 		case ICElement.C_PROJECT:
 			// Find the appropriate indexer and pass the delta on
@@ -62,12 +86,77 @@ public class CModelListener implements IElementChangedListener, IResourceChangeL
 			case ICElementDelta.ADDED:
 				fManager.addProject(project);
 		    	break;
+		    	
 			case ICElementDelta.CHANGED:
-				fManager.changeProject(project, delta);
+				processProjectDelta(project, delta, changeMap);
 				break;
+				
 			case ICElementDelta.REMOVED:
 				fManager.removeProject(project, delta);
-				break;
+		    	break;
+			}
+		}
+	}
+
+	private void processProjectDelta(ICProject project, ICElementDelta delta, HashMap changeMap) {
+		IPDOMIndexer indexer = fManager.getIndexer(project);
+		if (indexer != null && indexer.getID().equals(IPDOMManager.ID_NO_INDEXER)) {
+			return;
+		}
+		
+		DeltaAnalyzer deltaAnalyzer = new DeltaAnalyzer();
+		try {
+			deltaAnalyzer.analyzeDelta(delta);
+		} catch (CoreException e) {
+			CCorePlugin.log(e);
+		}
+		changeMap.put(project, deltaAnalyzer);
+	}
+
+	private void addLastRecentlyUsed(HashMap changeMap) {
+		boolean addLRUs= false;
+		int count= 0;
+		ITranslationUnit[] newLRUs= new ITranslationUnit[UPDATE_LR_CHANGED_FILES_COUNT];
+		
+		for (Iterator iterator = changeMap.values().iterator(); iterator.hasNext();) {
+			DeltaAnalyzer analyzer = (DeltaAnalyzer) iterator.next();
+			List l= analyzer.getAddedList();
+			for (Iterator it = l.iterator(); it.hasNext();) {
+				ITranslationUnit tu= (ITranslationUnit) it.next();
+				newLRUs[count++ % UPDATE_LR_CHANGED_FILES_COUNT]= tu;
+				if (!addLRUs && tu.isHeaderUnit()) {
+					addLRUs= true;
+				}
+			}
+			l= analyzer.getChangedList();
+			for (Iterator it = l.iterator(); it.hasNext();) {
+				ITranslationUnit tu= (ITranslationUnit) it.next();
+				newLRUs[count++ % UPDATE_LR_CHANGED_FILES_COUNT]= tu;
+				if (!addLRUs && tu.isHeaderUnit()) {
+					addLRUs= true;
+				}
+			}
+		}
+		
+		if (count > 0) {
+			if (addLRUs) {
+				for (Iterator it = fLRUs.keySet().iterator(); it.hasNext();) {
+					final ITranslationUnit tu = (ITranslationUnit) it.next();
+					if (tu.getResource().exists()) {
+						final ICProject cproject= tu.getCProject();
+						DeltaAnalyzer analyzer= (DeltaAnalyzer) changeMap.get(cproject);
+						if (analyzer == null) {
+							analyzer= new DeltaAnalyzer();
+							changeMap.put(cproject, analyzer);
+						}
+						analyzer.getChangedList().add(tu);
+					}
+				}
+			}
+			count= Math.min(count, newLRUs.length);
+			for (int i = 0; i < count; i++) {
+				final ITranslationUnit tu = newLRUs[i];
+				fLRUs.put(tu, tu);
 			}
 		}
 	}
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMManager.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMManager.java
index aec982e1071..f40d73101bd 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMManager.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMManager.java
@@ -63,7 +63,6 @@ import org.eclipse.cdt.internal.core.index.provider.IndexProviderManager;
 import org.eclipse.cdt.internal.core.pdom.PDOM.IListener;
 import org.eclipse.cdt.internal.core.pdom.db.ChunkCache;
 import org.eclipse.cdt.internal.core.pdom.dom.PDOMProjectIndexLocationConverter;
-import org.eclipse.cdt.internal.core.pdom.indexer.DeltaAnalyzer;
 import org.eclipse.cdt.internal.core.pdom.indexer.IndexerPreferences;
 import org.eclipse.cdt.internal.core.pdom.indexer.PDOMRebuildTask;
 import org.eclipse.cdt.internal.core.pdom.indexer.PDOMUpdateTask;
@@ -471,7 +470,7 @@ public class PDOMManager implements IWritableIndexManager, IListener {
 		createPolicy(project).setIndexer(indexer);
 	}
 
-	private IPDOMIndexer getIndexer(ICProject project) {
+	IPDOMIndexer getIndexer(ICProject project) {
 		assert !Thread.holdsLock(fProjectToPDOM);
 		synchronized (fUpdatePolicies) {
 			IndexUpdatePolicy policy= getPolicy(project);
@@ -724,18 +723,13 @@ public class PDOMManager implements IWritableIndexManager, IListener {
 		}
 	}
 
-	void changeProject(ICProject project, ICElementDelta delta) throws CoreException {
+	void changeProject(ICProject project, ITranslationUnit[] added, ITranslationUnit[] changed, ITranslationUnit[] removed) {
 		assert !Thread.holdsLock(fProjectToPDOM);
 		IPDOMIndexer indexer = getIndexer(project);
 		if (indexer != null && indexer.getID().equals(IPDOMManager.ID_NO_INDEXER)) {
 			return;
 		}
 		
-		DeltaAnalyzer deltaAnalyzer = new DeltaAnalyzer();
-		deltaAnalyzer.analyzeDelta(delta);
-		ITranslationUnit[] added= deltaAnalyzer.getAddedTUs();
-		ITranslationUnit[] changed= deltaAnalyzer.getChangedTUs();
-		ITranslationUnit[] removed= deltaAnalyzer.getRemovedTUs();
 		if (added.length > 0 || changed.length > 0 || removed.length > 0) {
 			synchronized (fUpdatePolicies) {
 				IndexUpdatePolicy policy= createPolicy(project);
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/indexer/DeltaAnalyzer.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/indexer/DeltaAnalyzer.java
index 9e6601df389..812f23fd43d 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/indexer/DeltaAnalyzer.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/indexer/DeltaAnalyzer.java
@@ -88,4 +88,12 @@ public class DeltaAnalyzer {
 	public ITranslationUnit[] getRemovedTUs() {
 		return (ITranslationUnit[]) fRemoved.toArray(new ITranslationUnit[fRemoved.size()]);
 	}
+
+	public List getAddedList() {
+		return fAdded;
+	}
+
+	public List getChangedList() {
+		return fChanged;
+	}
 }