diff --git a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
index 22ec3ae84d71..de8f17bd4ee5 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
@@ -76,8 +76,9 @@ public final class FileBasedIndexProjectHandler {
       indicator.setIndeterminate(false);
       indicator.setText(IndexingBundle.message("progress.indexing.updating"));
 
+      String indexingReason = "On refresh of files in " + myProject.getName();
       ProjectIndexingHistoryImpl projectIndexingHistory = new ProjectIndexingHistoryImpl(myProject,
-                                                                                         "On refresh of files in " + myProject.getName(),
+                                                                                         indexingReason,
                                                                                          ScanningType.REFRESH);
 
       IndexDiagnosticDumper.getInstance().onIndexingStarted(projectIndexingHistory);
@@ -109,7 +110,7 @@ public final class FileBasedIndexProjectHandler {
         //
         // Fair amount of FileBasedIndexProjectHandler.scheduleReindexingInDumbMode invocations are observed during massive refresh (e.g. branch change).
         // In practice, we observe 2-3 scanning tasks followed by a single indexing task.
-        new UnindexedFilesIndexer(myProject, files).indexFiles(projectIndexingHistory, indicator);
+        new UnindexedFilesIndexer(myProject, files, indexingReason).indexFiles(projectIndexingHistory, indicator);
       }
       catch (Exception e) {
         projectIndexingHistory.setWasInterrupted(true);
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/PerProjectIndexingQueue.kt b/platform/lang-impl/src/com/intellij/util/indexing/PerProjectIndexingQueue.kt
index 295f95a95597..b1a72edb0160 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/PerProjectIndexingQueue.kt
+++ b/platform/lang-impl/src/com/intellij/util/indexing/PerProjectIndexingQueue.kt
@@ -201,11 +201,11 @@ class PerProjectIndexingQueue(private val project: Project) : Disposable {
     }
   }
 
-  fun flushNow() {
+  fun flushNow(reason: String) {
     val (filesInQueue, totalFiles, currentLatch) = getAndResetQueuedFiles()
     try {
       if (totalFiles > 0) {
-        UnindexedFilesIndexer(project, filesInQueue).queue(project)
+        UnindexedFilesIndexer(project, filesInQueue, reason).queue(project)
       }
       else {
         LOG.info("Finished for " + project.name + ". No files to index with loading content.")
@@ -219,7 +219,8 @@ class PerProjectIndexingQueue(private val project: Project) : Disposable {
     val (filesInQueue, totalFiles, currentLatch) = getAndResetQueuedFiles()
     try {
       if (totalFiles > 0) {
-        UnindexedFilesIndexer(project, filesInQueue).indexFiles(projectIndexingHistory, indicator)
+        val indexingReason = projectIndexingHistory.indexingReason ?: "Flushing queue of project ${project.name}"
+        UnindexedFilesIndexer(project, filesInQueue, indexingReason).indexFiles(projectIndexingHistory, indicator)
       }
       else {
         LOG.info("Finished for " + project.name + ". No files to index with loading content.")
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesIndexer.java b/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesIndexer.java
index 6c552c902d92..2364e5782ccb 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesIndexer.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesIndexer.java
@@ -22,6 +22,7 @@ import com.intellij.util.indexing.diagnostic.ProjectIndexingHistoryImpl;
 import com.intellij.util.indexing.diagnostic.ScanningType;
 import com.intellij.util.indexing.roots.IndexableFilesIterator;
 import com.intellij.util.indexing.snapshot.SnapshotInputMappingsStatistics;
+import org.jetbrains.annotations.NonNls;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.TestOnly;
@@ -33,12 +34,15 @@ class UnindexedFilesIndexer extends DumbModeTask {
   private final Project myProject;
   private final FileBasedIndexImpl myIndex;
   private final Map<IndexableFilesIterator, Collection<VirtualFile>> providerToFiles;
+  private final @NonNls @NotNull String indexingReason;
 
   UnindexedFilesIndexer(Project project,
-                        Map<IndexableFilesIterator, Collection<VirtualFile>> providerToFiles) {
+                        Map<IndexableFilesIterator, Collection<VirtualFile>> providerToFiles,
+                        @NonNls @NotNull String indexingReason) {
     myProject = project;
     myIndex = (FileBasedIndexImpl)FileBasedIndex.getInstance();
     this.providerToFiles = providerToFiles;
+    this.indexingReason = indexingReason;
   }
 
   void indexFiles(@NotNull ProjectIndexingHistoryImpl projectIndexingHistory,
@@ -124,7 +128,7 @@ class UnindexedFilesIndexer extends DumbModeTask {
     if (!IndexInfrastructure.hasIndices()) {
       return;
     }
-    ProjectIndexingHistoryImpl projectIndexingHistory = new ProjectIndexingHistoryImpl(myProject, "Async indexing", ScanningType.REFRESH);
+    ProjectIndexingHistoryImpl projectIndexingHistory = new ProjectIndexingHistoryImpl(myProject, indexingReason, ScanningType.REFRESH);
     IndexDiagnosticDumper.getInstance().onIndexingStarted(projectIndexingHistory);
     ProgressSuspender suspender = ProgressSuspender.getSuspender(indicator);
     if (suspender != null) {
@@ -173,7 +177,10 @@ class UnindexedFilesIndexer extends DumbModeTask {
       mergedFilesToIndex.put(e.getKey(), mergedList);
     }
 
-    return new UnindexedFilesIndexer(myProject, mergedFilesToIndex);
+    String mergedReason = "Merged " + StringUtil.trimStart(indexingReason, "Merged ") +
+             " with " + StringUtil.trimStart(otherIndexingTask.indexingReason, "Merged ");
+
+    return new UnindexedFilesIndexer(myProject, mergedFilesToIndex, mergedReason);
   }
 
   private static double getPowerForSmoothProgressIndicator() {
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesScanner.java b/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesScanner.java
index 688a1044b940..751ab64fa075 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesScanner.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/UnindexedFilesScanner.java
@@ -259,7 +259,7 @@ public class UnindexedFilesScanner implements MergeableQueueTask<UnindexedFilesS
 
     if (shouldScanInSmartMode()) {
       // Switch to dumb mode and index
-      myProject.getService(PerProjectIndexingQueue.class).flushNow();
+      myProject.getService(PerProjectIndexingQueue.class).flushNow(myIndexingReason);
     }
     else {
       // Already in dumb mode. Just invoke indexer
diff --git a/platform/lang-impl/testSources/com/intellij/util/indexing/ScanningIndexingTasksMergeTest.java b/platform/lang-impl/testSources/com/intellij/util/indexing/ScanningIndexingTasksMergeTest.java
index c4a773cc5e27..3b9f69774876 100644
--- a/platform/lang-impl/testSources/com/intellij/util/indexing/ScanningIndexingTasksMergeTest.java
+++ b/platform/lang-impl/testSources/com/intellij/util/indexing/ScanningIndexingTasksMergeTest.java
@@ -51,8 +51,8 @@ public class ScanningIndexingTasksMergeTest extends LightPlatformTestCase {
     map2.put(iter2, f2);
     map2.put(iterShared, fShared.subList(1, 3));
 
-    task1 = new UnindexedFilesIndexer(getProject(), map1);
-    task2 = new UnindexedFilesIndexer(getProject(), map2);
+    task1 = new UnindexedFilesIndexer(getProject(), map1, "test task1");
+    task2 = new UnindexedFilesIndexer(getProject(), map2, "test task2");
   }
 
   public void testTryMergeIndexingTasks() {