SOLR-10130 Serious performance degradation in Solr 6.4.1 due to the

new metrics collection.

solr/CHANGES.txt

@@ -205,6 +205,28 @@ Other Changes
 * SOLR-9890: factor out ShardResultTransformerUtils.[un]marshSortValue methods
   (Judith Silverman, Christine Poerschke)
 
+==================  6.4.2 ==================
+
+Consult the LUCENE_CHANGES.txt file for additional, low level, changes in this release.
+
+Versions of Major Components
+---------------------
+Apache Tika 1.13
+Carrot2 3.15.0
+Velocity 1.7 and Velocity Tools 2.0
+Apache UIMA 2.3.1
+Apache ZooKeeper 3.4.6
+Jetty 9.3.14.v20161028
+
+Detailed Change List
+----------------------
+
+Bug Fixes
+----------------------
+* SOLR-10130: Serious performance degradation in Solr 6.4.1 due to the new metrics collection.
+  Default settings in solrconfig.xml /config/indexConfig/metrics have been changed to turn off
+  IndexWriter and Directory level metrics collection. (ab, ishan)
+
 ==================  6.4.1 ==================
 
 Consult the LUCENE_CHANGES.txt file for additional, low level, changes in this release.

solr/core/src/java/org/apache/solr/core/MetricsDirectoryFactory.java

@@ -40,6 +40,7 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
   private final String registry;
   private final DirectoryFactory in;
   private boolean directoryDetails = false;
+  private boolean directoryTotals = false;
 
   public MetricsDirectoryFactory(SolrMetricManager metricManager, String registry, DirectoryFactory in) {
     this.metricManager = metricManager;
@@ -54,9 +55,12 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
   /**
    * Currently the following arguments are supported:
    * <ul>
-   *   <li><code>directoryDetails</code> - (optional bool) when true then additional detailed metrics
+   *   <li><code>directory</code> - (optional bool, default false) when true then coarse-grained metrics will be collected.</li>
+   *   <li><code>directoryDetails</code> - (optional bool, default false) when true then additional detailed metrics
    *   will be collected. These include eg. IO size histograms and per-file counters and histograms</li>
    * </ul>
+   * NOTE: please be aware that collecting even coarse-grained metrics can have significant performance impact
+   * (see SOLR-10130).
    * @param args init args
    */
   @Override
@@ -66,12 +70,21 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     if (args == null) {
       return;
     }
+    Boolean td = args.getBooleanArg("directory");
+    if (td != null) {
+      directoryTotals = td;
+    } else {
+      directoryTotals = false;
+    }
     Boolean dd = args.getBooleanArg("directoryDetails");
     if (dd != null) {
       directoryDetails = dd;
     } else {
       directoryDetails = false;
     }
+    if (directoryDetails) {
+      directoryTotals = true;
+    }
   }
 
   /**
@@ -107,7 +120,7 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
   @Override
   protected Directory create(String path, LockFactory lockFactory, DirContext dirContext) throws IOException {
     Directory dir = in.create(path, lockFactory, dirContext);
-    return new MetricsDirectory(metricManager, registry, dir, directoryDetails);
+    return new MetricsDirectory(metricManager, registry, dir, directoryTotals, directoryDetails);
   }
 
   @Override
@@ -196,7 +209,7 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     if (dir instanceof MetricsDirectory) {
       return dir;
     } else {
-      return new MetricsDirectory(metricManager, registry, dir, directoryDetails);
+      return new MetricsDirectory(metricManager, registry, dir, directoryTotals, directoryDetails);
     }
   }
 
@@ -263,21 +276,31 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     private final Meter totalWrites;
     private final Histogram totalWriteSizes;
     private final boolean directoryDetails;
+    private final boolean directoryTotals;
 
     private final String PREFIX = SolrInfoMBean.Category.DIRECTORY.toString() + ".";
 
-    public MetricsDirectory(SolrMetricManager metricManager, String registry, Directory in, boolean directoryDetails) throws IOException {
+    public MetricsDirectory(SolrMetricManager metricManager, String registry, Directory in, boolean directoryTotals,
+                            boolean directoryDetails) throws IOException {
       super(in);
       this.metricManager = metricManager;
       this.registry = registry;
       this.in = in;
       this.directoryDetails = directoryDetails;
-      this.totalReads = metricManager.meter(registry, "reads", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+      this.directoryTotals = directoryTotals;
-      this.totalWrites = metricManager.meter(registry, "writes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+      if (directoryTotals) {
-      if (directoryDetails) {
+        this.totalReads = metricManager.meter(registry, "reads", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
-        this.totalReadSizes = metricManager.histogram(registry, "readSizes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+        this.totalWrites = metricManager.meter(registry, "writes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
-        this.totalWriteSizes = metricManager.histogram(registry, "writeSizes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+        if (directoryDetails) {
+          this.totalReadSizes = metricManager.histogram(registry, "readSizes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+          this.totalWriteSizes = metricManager.histogram(registry, "writeSizes", SolrInfoMBean.Category.DIRECTORY.toString(), "total");
+        } else {
+          this.totalReadSizes = null;
+          this.totalWriteSizes = null;
+        }
       } else {
+        this.totalReads = null;
+        this.totalWrites = null;
         this.totalReadSizes = null;
         this.totalWriteSizes = null;
       }
@@ -312,6 +335,9 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     @Override
     public IndexOutput createOutput(String name, IOContext context) throws IOException {
       IndexOutput output = in.createOutput(name, context);
+      if (!directoryTotals) {
+        return output;
+      }
       if (output != null) {
         return new MetricsOutput(totalWrites, totalWriteSizes, metricManager, registry, getMetricName(name, true), output);
       } else {
@@ -322,6 +348,9 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     @Override
     public IndexOutput createTempOutput(String prefix, String suffix, IOContext context) throws IOException {
       IndexOutput output = in.createTempOutput(prefix, suffix, context);
+      if (!directoryTotals) {
+        return output;
+      }
       if (output != null) {
         return new MetricsOutput(totalWrites, totalWriteSizes, metricManager, registry, getMetricName(TEMP, true), output);
       } else {
@@ -332,6 +361,9 @@ public class MetricsDirectoryFactory extends DirectoryFactory implements SolrCor
     @Override
     public IndexInput openInput(String name, IOContext context) throws IOException {
       IndexInput input = in.openInput(name, context);
+      if (!directoryTotals) {
+        return input;
+      }
       if (input != null) {
         return new MetricsInput(totalReads, totalReadSizes, metricManager, registry, getMetricName(name, false), input);
       } else {

solr/core/src/java/org/apache/solr/update/SolrIndexWriter.java

@@ -71,25 +71,26 @@ public class SolrIndexWriter extends IndexWriter {
 
   // metrics
   private long majorMergeDocs = 512 * 1024;
-  private final Timer majorMerge;
+  private Timer majorMerge;
-  private final Timer minorMerge;
+  private Timer minorMerge;
-  private final Meter majorMergedDocs;
+  private Meter majorMergedDocs;
-  private final Meter majorDeletedDocs;
+  private Meter majorDeletedDocs;
-  private final Counter mergeErrors;
+  private Counter mergeErrors;
-  private final Meter flushMeter; // original counter is package-private in IndexWriter
+  private Meter flushMeter; // original counter is package-private in IndexWriter
-  private final boolean mergeDetails;
+  private boolean mergeTotals = false;
+  private boolean mergeDetails = false;
   private final AtomicInteger runningMajorMerges = new AtomicInteger();
-  private final Gauge<Integer> runningMajorMergesGauge;
+  private Gauge<Integer> runningMajorMergesGauge;
   private final AtomicInteger runningMinorMerges = new AtomicInteger();
-  private final Gauge<Integer> runningMinorMergesGauge;
+  private Gauge<Integer> runningMinorMergesGauge;
   private final AtomicInteger runningMajorMergesSegments = new AtomicInteger();
-  private final Gauge<Integer> runningMajorMergesSegmentsGauge;
+  private Gauge<Integer> runningMajorMergesSegmentsGauge;
   private final AtomicInteger runningMinorMergesSegments = new AtomicInteger();
-  private final Gauge<Integer> runningMinorMergesSegmentsGauge;
+  private Gauge<Integer> runningMinorMergesSegmentsGauge;
   private final AtomicLong runningMajorMergesDocs = new AtomicLong();
-  private final Gauge<Long> runningMajorMergesDocsGauge;
+  private Gauge<Long> runningMajorMergesDocsGauge;
   private final AtomicLong runningMinorMergesDocs = new AtomicLong();
-  private final Gauge<Long> runningMinorMergesDocsGauge;
+  private Gauge<Long> runningMinorMergesDocsGauge;
 
   public static SolrIndexWriter create(SolrCore core, String name, String path, DirectoryFactory directoryFactory, boolean create, IndexSchema schema, SolrIndexConfig config, IndexDeletionPolicy delPolicy, Codec codec) throws IOException {
 
@@ -116,18 +117,7 @@ public class SolrIndexWriter extends IndexWriter {
     numOpens.incrementAndGet();
     log.debug("Opened Writer " + name);
     // no metrics
-    minorMerge = null;
+    mergeTotals = false;
-    majorMerge = null;
-    mergeErrors = null;
-    majorMergedDocs = null;
-    majorDeletedDocs = null;
-    runningMinorMergesGauge = null;
-    runningMinorMergesDocsGauge = null;
-    runningMinorMergesSegmentsGauge = null;
-    runningMajorMergesGauge = null;
-    runningMajorMergesDocsGauge = null;
-    runningMajorMergesSegmentsGauge = null;
-    flushMeter = null;
     mergeDetails = false;
   }
 
@@ -144,22 +134,6 @@ public class SolrIndexWriter extends IndexWriter {
     numOpens.incrementAndGet();
     SolrMetricManager metricManager = core.getCoreDescriptor().getCoreContainer().getMetricManager();
     String registry = core.getCoreMetricManager().getRegistryName();
-    minorMerge = metricManager.timer(registry, "minor", SolrInfoMBean.Category.INDEX.toString(), "merge");
-    majorMerge = metricManager.timer(registry, "major", SolrInfoMBean.Category.INDEX.toString(), "merge");
-    mergeErrors = metricManager.counter(registry, "errors", SolrInfoMBean.Category.INDEX.toString(), "merge");
-    runningMajorMergesGauge = () -> runningMajorMerges.get();
-    runningMinorMergesGauge = () -> runningMinorMerges.get();
-    runningMajorMergesDocsGauge = () -> runningMajorMergesDocs.get();
-    runningMinorMergesDocsGauge = () -> runningMinorMergesDocs.get();
-    runningMajorMergesSegmentsGauge = () -> runningMajorMergesSegments.get();
-    runningMinorMergesSegmentsGauge = () -> runningMinorMergesSegments.get();
-    metricManager.register(registry, runningMajorMergesGauge, true, "running", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
-    metricManager.register(registry, runningMinorMergesGauge, true, "running", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
-    metricManager.register(registry, runningMajorMergesDocsGauge, true, "running.docs", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
-    metricManager.register(registry, runningMinorMergesDocsGauge, true, "running.docs", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
-    metricManager.register(registry, runningMajorMergesSegmentsGauge, true, "running.segments", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
-    metricManager.register(registry, runningMinorMergesSegmentsGauge, true, "running.segments", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
-    flushMeter = metricManager.meter(registry, "flush", SolrInfoMBean.Category.INDEX.toString());
     if (config.metricsInfo != null && config.metricsInfo.initArgs != null) {
       Object v = config.metricsInfo.initArgs.get("majorMergeDocs");
       if (v != null) {
@@ -169,23 +143,41 @@ public class SolrIndexWriter extends IndexWriter {
           log.warn("Invalid 'majorMergeDocs' argument, using default 512k", e);
         }
       }
+      Boolean Totals = config.metricsInfo.initArgs.getBooleanArg("merge");
       Boolean Details = config.metricsInfo.initArgs.getBooleanArg("mergeDetails");
       if (Details != null) {
         mergeDetails = Details;
       } else {
         mergeDetails = false;
       }
+      if (Totals != null) {
+        mergeTotals = Totals;
+      } else {
+        mergeTotals = false;
+      }
       if (mergeDetails) {
+        mergeTotals = true; // override
         majorMergedDocs = metricManager.meter(registry, "docs", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
         majorDeletedDocs = metricManager.meter(registry, "deletedDocs", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
-      } else {
-        majorMergedDocs = null;
-        majorDeletedDocs = null;
       }
-    } else {
+      if (mergeTotals) {
-      mergeDetails = false;
+        minorMerge = metricManager.timer(registry, "minor", SolrInfoMBean.Category.INDEX.toString(), "merge");
-      majorMergedDocs = null;
+        majorMerge = metricManager.timer(registry, "major", SolrInfoMBean.Category.INDEX.toString(), "merge");
-      majorDeletedDocs = null;
+        mergeErrors = metricManager.counter(registry, "errors", SolrInfoMBean.Category.INDEX.toString(), "merge");
+        runningMajorMergesGauge = () -> runningMajorMerges.get();
+        runningMinorMergesGauge = () -> runningMinorMerges.get();
+        runningMajorMergesDocsGauge = () -> runningMajorMergesDocs.get();
+        runningMinorMergesDocsGauge = () -> runningMinorMergesDocs.get();
+        runningMajorMergesSegmentsGauge = () -> runningMajorMergesSegments.get();
+        runningMinorMergesSegmentsGauge = () -> runningMinorMergesSegments.get();
+        metricManager.register(registry, runningMajorMergesGauge, true, "running", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
+        metricManager.register(registry, runningMinorMergesGauge, true, "running", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
+        metricManager.register(registry, runningMajorMergesDocsGauge, true, "running.docs", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
+        metricManager.register(registry, runningMinorMergesDocsGauge, true, "running.docs", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
+        metricManager.register(registry, runningMajorMergesSegmentsGauge, true, "running.segments", SolrInfoMBean.Category.INDEX.toString(), "merge", "major");
+        metricManager.register(registry, runningMinorMergesSegmentsGauge, true, "running.segments", SolrInfoMBean.Category.INDEX.toString(), "merge", "minor");
+        flushMeter = metricManager.meter(registry, "flush", SolrInfoMBean.Category.INDEX.toString());
+      }
     }
   }
 
@@ -205,6 +197,10 @@ public class SolrIndexWriter extends IndexWriter {
   // we override this method to collect metrics for merges.
   @Override
   public void merge(MergePolicy.OneMerge merge) throws IOException {
+    if (!mergeTotals) {
+      super.merge(merge);
+      return;
+    }
     long deletedDocs = 0;
     long totalNumDocs = merge.totalNumDocs();
     for (SegmentCommitInfo info : merge.segments) {
@@ -251,7 +247,7 @@ public class SolrIndexWriter extends IndexWriter {
   @Override
   protected void doAfterFlush() throws IOException {
     if (flushMeter != null) { // this is null when writer is used only for snapshot cleanup
-      flushMeter.mark();
+      flushMeter.mark();      // or if mergeTotals == false
     }
     super.doAfterFlush();
   }

solr/core/src/test-files/solr/collection1/conf/solrconfig-indexmetrics.xml

@@ -29,8 +29,10 @@
 
   <indexConfig>
     <metrics>
-      <bool name="directoryDetails">${solr.tests.directoryDetails:false}</bool>
+      <bool name="directory">${solr.tests.metrics.directory:false}</bool>
-      <bool name="mergeDetails">${solr.tests.mergeDetails:false}</bool>
+      <bool name="directoryDetails">${solr.tests.metrics.directoryDetails:false}</bool>
+      <bool name="merge">${solr.tests.metrics.merge:false}</bool>
+      <bool name="mergeDetails">${solr.tests.metrics.mergeDetails:false}</bool>
     </metrics>
     <!-- intentionally set very low values here to trigger multiple flushes and merges.
          DO NOT USE THESE ABSURD VALUES IN PRODUCTION. -->

solr/core/src/test/org/apache/solr/update/SolrIndexMetricsTest.java

@@ -26,7 +26,7 @@ import com.codahale.metrics.Timer;
 import org.apache.solr.SolrTestCaseJ4;
 import org.apache.solr.common.SolrInputDocument;
 import org.apache.solr.request.SolrQueryRequest;
-import org.junit.BeforeClass;
+import org.junit.After;
 import org.junit.Test;
 
 /**
@@ -34,15 +34,12 @@ import org.junit.Test;
  */
 public class SolrIndexMetricsTest extends SolrTestCaseJ4 {
 
-  @BeforeClass
+  @After
-  public static void beforeClass() throws Exception {
+  public void afterMethod() throws Exception {
-    System.setProperty("solr.tests.mergeDetails", "true");
+    deleteCore();
-    System.setProperty("solr.tests.directoryDetails", "true");
-    initCore("solrconfig-indexmetrics.xml", "schema.xml");
   }
 
-  @Test
+  private void addDocs() throws Exception {
-  public void testIndexMetrics() throws Exception {
     SolrQueryRequest req = lrf.makeRequest();
     UpdateHandler uh = req.getCore().getUpdateHandler();
     AddUpdateCommand add = new AddUpdateCommand(req);
@@ -54,10 +51,86 @@ public class SolrIndexMetricsTest extends SolrTestCaseJ4 {
       uh.addDoc(add);
     }
     uh.commit(new CommitUpdateCommand(req, false));
-    MetricRegistry registry = h.getCoreContainer().getMetricManager().registry(h.getCore().getCoreMetricManager().getRegistryName());
-    assertNotNull(registry);
     // make sure all merges are finished
     h.reload();
+  }
+
+  @Test
+  public void testIndexMetricsNoDetails() throws Exception {
+    System.setProperty("solr.tests.metrics.merge", "true");
+    System.setProperty("solr.tests.metrics.mergeDetails", "false");
+    System.setProperty("solr.tests.metrics.directory", "true");
+    System.setProperty("solr.tests.metrics.directoryDetails", "false");
+    initCore("solrconfig-indexmetrics.xml", "schema.xml");
+
+    addDocs();
+
+    MetricRegistry registry = h.getCoreContainer().getMetricManager().registry(h.getCore().getCoreMetricManager().getRegistryName());
+    assertNotNull(registry);
+
+    Map<String, Metric> metrics = registry.getMetrics();
+
+    assertEquals(10, metrics.entrySet().stream().filter(e -> e.getKey().startsWith("INDEX")).count());
+    assertEquals(2, metrics.entrySet().stream().filter(e -> e.getKey().startsWith("DIRECTORY")).count());
+
+    // check basic index meters
+    Timer timer = (Timer)metrics.get("INDEX.merge.minor");
+    assertTrue("minorMerge: " + timer.getCount(), timer.getCount() >= 3);
+    timer = (Timer)metrics.get("INDEX.merge.major");
+    assertEquals("majorMerge: " + timer.getCount(), 0, timer.getCount());
+    // check detailed meters
+    assertNull((Meter)metrics.get("INDEX.merge.major.docs"));
+    Meter meter = (Meter)metrics.get("INDEX.flush");
+    assertTrue("flush: " + meter.getCount(), meter.getCount() > 10);
+
+    // check basic directory meters
+    meter = (Meter)metrics.get("DIRECTORY.total.reads");
+    assertTrue("totalReads", meter.getCount() > 0);
+    meter = (Meter)metrics.get("DIRECTORY.total.writes");
+    assertTrue("totalWrites", meter.getCount() > 0);
+    // check detailed meters
+    Histogram histogram = (Histogram)metrics.get("DIRECTORY.total.readSizes");
+    assertNull("readSizes", histogram);
+    histogram = (Histogram)metrics.get("DIRECTORY.total.writeSizes");
+    assertNull("writeSizes", histogram);
+    meter = (Meter)metrics.get("DIRECTORY.segments.writes");
+    assertNull("segmentsWrites", meter);
+    histogram = (Histogram)metrics.get("DIRECTORY.segments.writeSizes");
+    assertNull("segmentsWriteSizes", histogram);
+
+  }
+
+  @Test
+  public void testIndexNoMetrics() throws Exception {
+    System.setProperty("solr.tests.metrics.merge", "false");
+    System.setProperty("solr.tests.metrics.mergeDetails", "false");
+    System.setProperty("solr.tests.metrics.directory", "false");
+    System.setProperty("solr.tests.metrics.directoryDetails", "false");
+    initCore("solrconfig-indexmetrics.xml", "schema.xml");
+
+    addDocs();
+
+    MetricRegistry registry = h.getCoreContainer().getMetricManager().registry(h.getCore().getCoreMetricManager().getRegistryName());
+    assertNotNull(registry);
+
+    Map<String, Metric> metrics = registry.getMetrics();
+    assertEquals(0, metrics.entrySet().stream().filter(e -> e.getKey().startsWith("INDEX")).count());
+    // this is variable, depending on the codec and the number of created files
+    assertEquals(0, metrics.entrySet().stream().filter(e -> e.getKey().startsWith("DIRECTORY")).count());
+  }
+
+  @Test
+  public void testIndexMetricsWithDetails() throws Exception {
+    System.setProperty("solr.tests.metrics.merge", "false"); // test mergeDetails override too
+    System.setProperty("solr.tests.metrics.mergeDetails", "true");
+    System.setProperty("solr.tests.metrics.directory", "false");
+    System.setProperty("solr.tests.metrics.directoryDetails", "true");
+    initCore("solrconfig-indexmetrics.xml", "schema.xml");
+
+    addDocs();
+
+    MetricRegistry registry = h.getCoreContainer().getMetricManager().registry(h.getCore().getCoreMetricManager().getRegistryName());
+    assertNotNull(registry);
 
     Map<String, Metric> metrics = registry.getMetrics();
 
@@ -70,8 +143,10 @@ public class SolrIndexMetricsTest extends SolrTestCaseJ4 {
     assertTrue("minorMerge: " + timer.getCount(), timer.getCount() >= 3);
     timer = (Timer)metrics.get("INDEX.merge.major");
     assertEquals("majorMerge: " + timer.getCount(), 0, timer.getCount());
+    // check detailed meters
     Meter meter = (Meter)metrics.get("INDEX.merge.major.docs");
     assertEquals("majorMergeDocs: " + meter.getCount(), 0, meter.getCount());
+
     meter = (Meter)metrics.get("INDEX.flush");
     assertTrue("flush: " + meter.getCount(), meter.getCount() > 10);
 
@@ -80,11 +155,11 @@ public class SolrIndexMetricsTest extends SolrTestCaseJ4 {
     assertTrue("totalReads", meter.getCount() > 0);
     meter = (Meter)metrics.get("DIRECTORY.total.writes");
     assertTrue("totalWrites", meter.getCount() > 0);
+    // check detailed meters
     Histogram histogram = (Histogram)metrics.get("DIRECTORY.total.readSizes");
     assertTrue("readSizes", histogram.getCount() > 0);
     histogram = (Histogram)metrics.get("DIRECTORY.total.writeSizes");
     assertTrue("writeSizes", histogram.getCount() > 0);
-    // check detailed meters
     meter = (Meter)metrics.get("DIRECTORY.segments.writes");
     assertTrue("segmentsWrites", meter.getCount() > 0);
     histogram = (Histogram)metrics.get("DIRECTORY.segments.writeSizes");