diff --git oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStats.java oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStats.java
index 0cc990c..7e55a3c 100644
--- oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStats.java
+++ oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStats.java
@@ -35,12 +35,14 @@ public class FileStoreStats implements FileStoreStatsMBean, FileStoreMonitor {
     public static final String SEGMENT_REPO_SIZE = "SEGMENT_REPO_SIZE";
     public static final String SEGMENT_WRITES = "SEGMENT_WRITES";
     public static final String JOURNAL_WRITES = "JOURNAL_WRITES";
+    public static final String CLEANUP_RECLAIMED_SIZE = "CLEANUP_RECLAIMED_SIZE";
     
     private final StatisticsProvider statisticsProvider;
     private final FileStore store;
     private final MeterStats writeStats;
     private final CounterStats repoSize;
     private final MeterStats journalWriteStats;
+    private final MeterStats reclaimedSizeStats;
     
     public FileStoreStats(StatisticsProvider statisticsProvider, FileStore store, long initialSize) {
         this.statisticsProvider = statisticsProvider;
@@ -48,6 +50,7 @@ public class FileStoreStats implements FileStoreStatsMBean, FileStoreMonitor {
         this.writeStats = statisticsProvider.getMeter(SEGMENT_WRITES, StatsOptions.DEFAULT);
         this.repoSize = statisticsProvider.getCounterStats(SEGMENT_REPO_SIZE, StatsOptions.DEFAULT);
         this.journalWriteStats = statisticsProvider.getMeter(JOURNAL_WRITES, StatsOptions.DEFAULT);
+        this.reclaimedSizeStats = statisticsProvider.getMeter(CLEANUP_RECLAIMED_SIZE, StatsOptions.DEFAULT);
         repoSize.inc(initialSize);
     }
 
@@ -62,6 +65,7 @@ public class FileStoreStats implements FileStoreStatsMBean, FileStoreMonitor {
     @Override
     public void reclaimed(long size) {
         repoSize.dec(size);
+        reclaimedSizeStats.mark(size);
     }
     
     @Override
@@ -110,6 +114,16 @@ public class FileStoreStats implements FileStoreStatsMBean, FileStoreMonitor {
     public CompositeData getJournalWriteStatsAsCompositeData() {
         return asCompositeData(getTimeSeries(JOURNAL_WRITES), JOURNAL_WRITES);
     }
+    
+    @Override
+    public long getReclaimedSizeStatsAsCount() {
+        return reclaimedSizeStats.getCount();
+    }
+    
+    @Override
+    public CompositeData getReclaimedSizeStatsAsCompositeData() {
+        return asCompositeData(getTimeSeries(CLEANUP_RECLAIMED_SIZE), CLEANUP_RECLAIMED_SIZE);
+    }
 
     private TimeSeries getTimeSeries(String name) {
         return statisticsProvider.getStats().getTimeSeries(name, true);
diff --git oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStatsMBean.java oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStatsMBean.java
index ba13c9a..5c68d10 100644
--- oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStatsMBean.java
+++ oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStoreStatsMBean.java
@@ -50,4 +50,14 @@ public interface FileStoreStatsMBean {
      * @return  time series of the writes to journal
      */
     CompositeData getJournalWriteStatsAsCompositeData();
+    
+    /**
+     * @return  count of the bytes reclaimed ever since during cleanup
+     */
+    long getReclaimedSizeStatsAsCount();
+    
+    /**
+     * @return  time series of the bytes reclaimed during cleanup
+     */
+    CompositeData getReclaimedSizeStatsAsCompositeData();
 }
diff --git oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
index 42ade59..933a637 100644
--- oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
+++ oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
@@ -46,6 +46,7 @@ import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.ScheduledExecutorService;
@@ -59,6 +60,7 @@ import org.apache.jackrabbit.oak.api.PropertyState;
 import org.apache.jackrabbit.oak.api.Type;
 import org.apache.jackrabbit.oak.segment.compaction.SegmentGCOptions;
 import org.apache.jackrabbit.oak.segment.file.FileStore;
+import org.apache.jackrabbit.oak.segment.file.FileStoreStats;
 import org.apache.jackrabbit.oak.spi.commit.CommitInfo;
 import org.apache.jackrabbit.oak.spi.commit.EmptyHook;
 import org.apache.jackrabbit.oak.spi.state.ChildNodeEntry;
@@ -66,6 +68,7 @@ import org.apache.jackrabbit.oak.spi.state.NodeBuilder;
 import org.apache.jackrabbit.oak.spi.state.NodeState;
 import org.apache.jackrabbit.oak.spi.state.NodeStore;
 import org.apache.jackrabbit.oak.stats.DefaultStatisticsProvider;
+import org.apache.jackrabbit.oak.stats.StatisticsProvider;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
@@ -924,6 +927,52 @@ public class CompactionAndCleanupIT {
             fileStore.close();
         }
     }
+    
+    /**
+     * Test asserting OAK-4106 : Concurrent writes during cleanup should not
+     * impact reclaimedSize computation.
+     */
+    @Test
+    public void concurrentWritesDuringCleanup() throws Exception {
+        ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
+        StatisticsProvider statsProvider = new DefaultStatisticsProvider(executor);
+
+        final FileStore fileStore = fileStoreBuilder(getFileStoreFolder())
+                .withGCOptions(defaultGCOptions().setRetainedGenerations(2)).withStatisticsProvider(statsProvider)
+                .withMaxFileSize(1).build();
+        FileStoreStats stats = new FileStoreStats(statsProvider, fileStore, 0);
+        final SegmentNodeStore nodeStore = SegmentNodeStoreBuilders.builder(fileStore).build();
+
+        try {
+            Runnable concurrentWriteTask = new Runnable() {
+                public void run() {
+                    try {
+                        NodeBuilder builder = nodeStore.getRoot().builder();
+                        builder.setProperty("blob" + new Random().nextInt(), createBlob(nodeStore, 512 * 512));
+
+                        nodeStore.merge(builder, EmptyHook.INSTANCE, CommitInfo.EMPTY);
+                        fileStore.flush();
+                    } catch (CommitFailedException e) {
+                        // ignore
+                    } catch (IOException e) {
+                        // ignore
+                    }
+                };
+            };
+
+            ExecutorService executorService = Executors.newFixedThreadPool(5);
+            for (int i = 0; i < 5; i++) {
+                executorService.execute(concurrentWriteTask);
+            }
+
+            fileStore.cleanup();
+
+            assertTrue(stats.getReclaimedSizeStatsAsCount() >= 0);
+
+        } finally {
+            fileStore.close();
+        }
+    }
 
     private static void addContent(NodeBuilder builder) {
         for (int k = 0; k < 10000; k++) {