Add Histogram0..3 to track bytes sent

The pack_bytes metric reports on the size of data sent to clients.
Using a histogram allows the server to track the distribution of these
files over time, as well as total amount sent.

The response_bytes metric reports on size of REST API replies,
broken down by view.

Change-Id: I7c06cb9afb2f4a8da1ef1eec85b5831f75b88116

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiMetrics.java

@@ -20,6 +20,7 @@ import com.google.gerrit.metrics.Counter1;
 import com.google.gerrit.metrics.Counter2;
 import com.google.gerrit.metrics.Description;
 import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram1;
 import com.google.gerrit.metrics.MetricMaker;
 import com.google.gerrit.metrics.Timer1;
 import com.google.gerrit.metrics.Description.Units;
@@ -36,6 +37,7 @@ public class RestApiMetrics {
   final Counter1<String> count;
   final Counter2<String, Integer> errorCount;
   final Timer1<String> serverLatency;
+  final Histogram1<String> responseBytes;
 
   @Inject
   RestApiMetrics(MetricMaker metrics) {
@@ -59,6 +61,13 @@ public class RestApiMetrics {
           .setCumulative()
           .setUnit(Units.MILLISECONDS),
         view);
+
+    responseBytes = metrics.newHistogram(
+        "http/server/rest_api/response_bytes",
+        new Description("Size of response on network (may be gzip compressed)")
+          .setCumulative()
+          .setUnit(Units.BYTES),
+        view);
   }
 
   String view(ViewData viewData) {

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java

@@ -43,6 +43,7 @@ import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Sets;
 import com.google.common.io.BaseEncoding;
+import com.google.common.io.CountingOutputStream;
 import com.google.common.math.IntMath;
 import com.google.common.net.HttpHeaders;
 import com.google.gerrit.audit.AuditService;
@@ -206,6 +207,7 @@ public class RestApiServlet extends HttpServlet {
     res.setHeader("Content-Disposition", "attachment");
     res.setHeader("X-Content-Type-Options", "nosniff");
     int status = SC_OK;
+    long responseBytes = -1;
     Object result = null;
     Multimap<String, String> params = LinkedHashMultimap.create();
     Object inputRequestBody = null;
@@ -353,46 +355,47 @@ public class RestApiServlet extends HttpServlet {
       if (result != Response.none()) {
         result = Response.unwrap(result);
         if (result instanceof BinaryResult) {
-          replyBinaryResult(req, res, (BinaryResult) result);
+          responseBytes = replyBinaryResult(req, res, (BinaryResult) result);
         } else {
-          replyJson(req, res, config, result);
+          responseBytes = replyJson(req, res, config, result);
         }
       }
     } catch (MalformedJsonException e) {
-      replyError(req, res, status = SC_BAD_REQUEST,
+      responseBytes = replyError(req, res, status = SC_BAD_REQUEST,
           "Invalid " + JSON_TYPE + " in request", e);
     } catch (JsonParseException e) {
-      replyError(req, res, status = SC_BAD_REQUEST,
+      responseBytes = replyError(req, res, status = SC_BAD_REQUEST,
           "Invalid " + JSON_TYPE + " in request", e);
     } catch (BadRequestException e) {
-      replyError(req, res, status = SC_BAD_REQUEST, messageOr(e, "Bad Request"),
+      responseBytes = replyError(req, res, status = SC_BAD_REQUEST,
-          e.caching(), e);
+          messageOr(e, "Bad Request"), e.caching(), e);
     } catch (AuthException e) {
-      replyError(req, res, status = SC_FORBIDDEN, messageOr(e, "Forbidden"),
+      responseBytes = replyError(req, res, status = SC_FORBIDDEN,
-          e.caching(), e);
+          messageOr(e, "Forbidden"), e.caching(), e);
     } catch (AmbiguousViewException e) {
-      replyError(req, res, status = SC_NOT_FOUND, messageOr(e, "Ambiguous"), e);
+      responseBytes = replyError(req, res, status = SC_NOT_FOUND,
+          messageOr(e, "Ambiguous"), e);
     } catch (ResourceNotFoundException e) {
-      replyError(req, res, status = SC_NOT_FOUND, messageOr(e, "Not Found"),
+      responseBytes = replyError(req, res, status = SC_NOT_FOUND,
-          e.caching(), e);
+          messageOr(e, "Not Found"), e.caching(), e);
     } catch (MethodNotAllowedException e) {
-      replyError(req, res, status = SC_METHOD_NOT_ALLOWED,
+      responseBytes = replyError(req, res, status = SC_METHOD_NOT_ALLOWED,
           messageOr(e, "Method Not Allowed"), e.caching(), e);
     } catch (ResourceConflictException e) {
-      replyError(req, res, status = SC_CONFLICT, messageOr(e, "Conflict"),
+      responseBytes = replyError(req, res, status = SC_CONFLICT,
-          e.caching(), e);
+          messageOr(e, "Conflict"), e.caching(), e);
     } catch (PreconditionFailedException e) {
-      replyError(req, res, status = SC_PRECONDITION_FAILED,
+      responseBytes = replyError(req, res, status = SC_PRECONDITION_FAILED,
           messageOr(e, "Precondition Failed"), e.caching(), e);
     } catch (UnprocessableEntityException e) {
-      replyError(req, res, status = 422, messageOr(e, "Unprocessable Entity"),
+      responseBytes = replyError(req, res, status = 422,
-          e.caching(), e);
+          messageOr(e, "Unprocessable Entity"), e.caching(), e);
     } catch (NotImplementedException e) {
-      replyError(req, res, status = SC_NOT_IMPLEMENTED,
+      responseBytes = replyError(req, res, status = SC_NOT_IMPLEMENTED,
           messageOr(e, "Not Implemented"), e);
     } catch (Exception e) {
       status = SC_INTERNAL_SERVER_ERROR;
-      handleException(e, req, res);
+      responseBytes = handleException(e, req, res);
     } finally {
       String metric = viewData != null && viewData.view != null
           ? globals.metrics.view(viewData)
@@ -401,6 +404,9 @@ public class RestApiServlet extends HttpServlet {
       if (status >= SC_BAD_REQUEST) {
         globals.metrics.errorCount.increment(metric, status);
       }
+      if (responseBytes != -1) {
+        globals.metrics.responseBytes.record(metric, responseBytes);
+      }
       globals.metrics.serverLatency.record(
           metric,
           System.nanoTime() - startNanos,
@@ -667,7 +673,7 @@ public class RestApiServlet extends HttpServlet {
     throw new InstantiationException("Cannot make " + type);
   }
 
-  public static void replyJson(@Nullable HttpServletRequest req,
+  public static long replyJson(@Nullable HttpServletRequest req,
       HttpServletResponse res,
       Multimap<String, String> config,
       Object result)
@@ -683,7 +689,7 @@ public class RestApiServlet extends HttpServlet {
     }
     w.write('\n');
     w.flush();
-    replyBinaryResult(req, res, asBinaryResult(buf)
+    return replyBinaryResult(req, res, asBinaryResult(buf)
       .setContentType(JSON_TYPE)
       .setCharacterEncoding(UTF_8));
   }
@@ -752,7 +758,7 @@ public class RestApiServlet extends HttpServlet {
   }
 
   @SuppressWarnings("resource")
-  static void replyBinaryResult(
+  static long replyBinaryResult(
       @Nullable HttpServletRequest req,
       HttpServletResponse res,
       BinaryResult bin) throws IOException {
@@ -783,10 +789,13 @@ public class RestApiServlet extends HttpServlet {
       }
 
       if (req == null || !"HEAD".equals(req.getMethod())) {
-        try (OutputStream dst = res.getOutputStream()) {
+        try (CountingOutputStream dst =
+            new CountingOutputStream(res.getOutputStream())) {
           bin.writeTo(dst);
+          return dst.getCount();
         }
       }
+      return 0;
     } finally {
       appResult.close();
     }
@@ -993,7 +1002,7 @@ public class RestApiServlet extends HttpServlet {
         viewData.pluginName, viewData.view.getClass());
   }
 
-  private static void handleException(Throwable err, HttpServletRequest req,
+  private static long handleException(Throwable err, HttpServletRequest req,
       HttpServletResponse res) throws IOException {
     String uri = req.getRequestURI();
     if (!Strings.isNullOrEmpty(req.getQueryString())) {
@@ -1003,16 +1012,17 @@ public class RestApiServlet extends HttpServlet {
 
     if (!res.isCommitted()) {
       res.reset();
-      replyError(req, res, SC_INTERNAL_SERVER_ERROR, "Internal server error", err);
+      return replyError(req, res, SC_INTERNAL_SERVER_ERROR, "Internal server error", err);
     }
+    return 0;
   }
 
-  public static void replyError(HttpServletRequest req, HttpServletResponse res,
+  public static long replyError(HttpServletRequest req, HttpServletResponse res,
       int statusCode, String msg, @Nullable Throwable err) throws IOException {
-    replyError(req, res, statusCode, msg, CacheControl.NONE, err);
+    return replyError(req, res, statusCode, msg, CacheControl.NONE, err);
   }
 
-  public static void replyError(HttpServletRequest req,
+  public static long replyError(HttpServletRequest req,
       HttpServletResponse res, int statusCode, String msg,
       CacheControl c, @Nullable Throwable err) throws IOException {
     if (err != null) {
@@ -1020,18 +1030,18 @@ public class RestApiServlet extends HttpServlet {
     }
     configureCaching(req, res, null, null, c);
     res.setStatus(statusCode);
-    replyText(req, res, msg);
+    return replyText(req, res, msg);
   }
 
-  static void replyText(@Nullable HttpServletRequest req,
+  static long replyText(@Nullable HttpServletRequest req,
       HttpServletResponse res, String text) throws IOException {
     if ((req == null || isGetOrHead(req)) && isMaybeHTML(text)) {
-      replyJson(req, res, ImmutableMultimap.of("pp", "0"), new JsonPrimitive(text));
+      return replyJson(req, res, ImmutableMultimap.of("pp", "0"), new JsonPrimitive(text));
     } else {
       if (!text.endsWith("\n")) {
         text += "\n";
       }
-      replyBinaryResult(req, res,
+      return replyBinaryResult(req, res,
           BinaryResult.create(text).setContentType("text/plain"));
     }
   }

gerrit-server/src/main/java/com/google/gerrit/metrics/DisabledMetricMaker.java

@@ -91,6 +91,41 @@ public class DisabledMetricMaker extends MetricMaker {
     };
   }
 
+  @Override
+  public Histogram0 newHistogram(String name, Description desc) {
+    return new Histogram0() {
+      @Override public void record(long value) {}
+      @Override public void remove() {}
+    };
+  }
+
+  @Override
+  public <F1> Histogram1<F1> newHistogram(String name, Description desc,
+      Field<F1> field1) {
+    return new Histogram1<F1>() {
+      @Override public void record(F1 field1, long value) {}
+      @Override public void remove() {}
+    };
+  }
+
+  @Override
+  public <F1, F2> Histogram2<F1, F2> newHistogram(String name, Description desc,
+      Field<F1> field1, Field<F2> field2) {
+    return new Histogram2<F1, F2>() {
+      @Override public void record(F1 field1, F2 field2, long value) {}
+      @Override public void remove() {}
+    };
+  }
+
+  @Override
+  public <F1, F2, F3> Histogram3<F1, F2, F3> newHistogram(String name,
+      Description desc, Field<F1> field1, Field<F2> field2, Field<F3> field3) {
+    return new Histogram3<F1, F2, F3>() {
+      @Override public void record(F1 field1, F2 field2, F3 field3, long value) {}
+      @Override public void remove() {}
+    };
+  }
+
   @Override
   public <V> CallbackMetric0<V> newCallbackMetric(String name,
       Class<V> valueClass, Description desc) {

gerrit-server/src/main/java/com/google/gerrit/metrics/Histogram0.java

@@ -0,0 +1,27 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics;
+
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+
+/**
+ * Measures the statistical distribution of values in a stream of data.
+ * <p>
+ * Suitable uses are "response size in bytes", etc.
+ */
+public abstract class Histogram0 implements RegistrationHandle {
+  /** Record a sample of a specified amount. */
+  public abstract void record(long value);
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/Histogram1.java

@@ -0,0 +1,29 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics;
+
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+
+/**
+ * Measures the statistical distribution of values in a stream of data.
+ * <p>
+ * Suitable uses are "response size in bytes", etc.
+ *
+ * @param <F1> type of the field.
+ */
+public abstract class Histogram1<F1> implements RegistrationHandle {
+  /** Record a sample of a specified amount. */
+  public abstract void record(F1 field1, long value);
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/Histogram2.java

@@ -0,0 +1,30 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics;
+
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+
+/**
+ * Measures the statistical distribution of values in a stream of data.
+ * <p>
+ * Suitable uses are "response size in bytes", etc.
+ *
+ * @param <F1> type of the field.
+ * @param <F2> type of the field.
+ */
+public abstract class Histogram2<F1, F2> implements RegistrationHandle {
+  /** Record a sample of a specified amount. */
+  public abstract void record(F1 field1, F2 field2, long value);
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/Histogram3.java

@@ -0,0 +1,31 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics;
+
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+
+/**
+ * Measures the statistical distribution of values in a stream of data.
+ * <p>
+ * Suitable uses are "response size in bytes", etc.
+ *
+ * @param <F1> type of the field.
+ * @param <F2> type of the field.
+ * @param <F3> type of the field.
+ */
+public abstract class Histogram3<F1, F2, F3> implements RegistrationHandle {
+  /** Record a sample of a specified amount. */
+  public abstract void record(F1 field1, F2 field2, F3 field3, long value);
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/MetricMaker.java

@@ -46,6 +46,18 @@ public abstract class MetricMaker {
       String name, Description desc,
       Field<F1> field1, Field<F2> field2, Field<F3> field3);
 
+  /** Metric statistical distribution of values. */
+  public abstract Histogram0 newHistogram(String name, Description desc);
+  public abstract <F1> Histogram1<F1> newHistogram(
+      String name, Description desc,
+      Field<F1> field1);
+  public abstract <F1, F2> Histogram2<F1, F2> newHistogram(
+      String name, Description desc,
+      Field<F1> field1, Field<F2> field2);
+  public abstract <F1, F2, F3> Histogram3<F1, F2, F3> newHistogram(
+      String name, Description desc,
+      Field<F1> field1, Field<F2> field2, Field<F3> field3);
+
   /**
    * Constant value that does not change.
    *

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/BucketedHistogram.java

@@ -0,0 +1,107 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics.dropwizard;
+
+import com.google.common.base.Function;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Maps;
+import com.google.gerrit.metrics.Description;
+import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.dropwizard.DropWizardMetricMaker.HistogramImpl;
+
+import com.codahale.metrics.Metric;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/** Abstract histogram broken down into buckets by {@link Field} values. */
+abstract class BucketedHistogram implements BucketedMetric {
+  private final DropWizardMetricMaker metrics;
+  private final String name;
+  private final Description.FieldOrdering ordering;
+  protected final Field<?>[] fields;
+  protected final HistogramImpl total;
+  private final Map<Object, HistogramImpl> cells;
+
+  BucketedHistogram(DropWizardMetricMaker metrics, String name,
+      Description desc, Field<?>... fields) {
+    this.metrics = metrics;
+    this.name = name;
+    this.ordering = desc.getFieldOrdering();
+    this.fields = fields;
+    this.total = metrics.newHistogramImpl(name + "_total");
+    this.cells = new ConcurrentHashMap<>();
+  }
+
+  void doRemove() {
+    for (HistogramImpl c : cells.values()) {
+      c.remove();
+    }
+    total.remove();
+    metrics.remove(name);
+  }
+
+  HistogramImpl forceCreate(Object f1, Object f2) {
+    return forceCreate(ImmutableList.of(f1, f2));
+  }
+
+  HistogramImpl forceCreate(Object f1, Object f2, Object f3) {
+    return forceCreate(ImmutableList.of(f1, f2, f3));
+  }
+
+  HistogramImpl forceCreate(Object key) {
+    HistogramImpl c = cells.get(key);
+    if (c != null) {
+      return c;
+    }
+
+    synchronized (cells) {
+      c = cells.get(key);
+      if (c == null) {
+        c = metrics.newHistogramImpl(submetric(key));
+        cells.put(key, c);
+      }
+      return c;
+    }
+  }
+
+  private String submetric(Object key) {
+    return DropWizardMetricMaker.name(ordering, name, name(key));
+  }
+
+  abstract String name(Object key);
+
+  @Override
+  public Metric getTotal() {
+    return total.metric;
+  }
+
+  @Override
+  public Field<?>[] getFields() {
+    return fields;
+  }
+
+  @Override
+  public Map<Object, Metric> getCells() {
+    return Maps.transformValues(
+        cells,
+        new Function<HistogramImpl, Metric> () {
+          @Override
+          public Metric apply(HistogramImpl in) {
+            return in.metric;
+          }
+        });
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/DropWizardMetricMaker.java

@@ -32,6 +32,10 @@ import com.google.gerrit.metrics.Counter3;
 import com.google.gerrit.metrics.Description;
 import com.google.gerrit.metrics.Description.FieldOrdering;
 import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram0;
+import com.google.gerrit.metrics.Histogram1;
+import com.google.gerrit.metrics.Histogram2;
+import com.google.gerrit.metrics.Histogram3;
 import com.google.gerrit.metrics.MetricMaker;
 import com.google.gerrit.metrics.Timer0;
 import com.google.gerrit.metrics.Timer1;
@@ -226,6 +230,56 @@ public class DropWizardMetricMaker extends MetricMaker {
     return new TimerImpl(name, registry.timer(name));
   }
 
+  @Override
+  public synchronized Histogram0 newHistogram(String name, Description desc) {
+    checkHistogramDescription(name, desc);
+    define(name, desc);
+    return newHistogramImpl(name);
+  }
+
+  @Override
+  public synchronized <F1> Histogram1<F1> newHistogram(String name,
+      Description desc, Field<F1> field1) {
+    checkHistogramDescription(name, desc);
+    HistogramImpl1<F1> m = new HistogramImpl1<>(this, name, desc, field1);
+    define(name, desc);
+    bucketed.put(name, m);
+    return m.histogram1();
+  }
+
+  @Override
+  public synchronized <F1, F2> Histogram2<F1, F2> newHistogram(String name,
+      Description desc, Field<F1> field1, Field<F2> field2) {
+    checkHistogramDescription(name, desc);
+    HistogramImplN m = new HistogramImplN(this, name, desc, field1, field2);
+    define(name, desc);
+    bucketed.put(name, m);
+    return m.histogram2();
+  }
+
+  @Override
+  public synchronized <F1, F2, F3> Histogram3<F1, F2, F3> newHistogram(
+      String name, Description desc,
+      Field<F1> field1, Field<F2> field2, Field<F3> field3) {
+    checkHistogramDescription(name, desc);
+    HistogramImplN m = new HistogramImplN(this, name, desc, field1, field2, field3);
+    define(name, desc);
+    bucketed.put(name, m);
+    return m.histogram3();
+  }
+
+  private static void checkHistogramDescription(String name, Description desc) {
+    checkMetricName(name);
+    checkArgument(!desc.isConstant(), "histogram must not be constant");
+    checkArgument(!desc.isGauge(), "histogram must not be a gauge");
+    checkArgument(!desc.isRate(), "histogram must not be a rate");
+    checkArgument(desc.isCumulative(), "histogram must be cumulative");
+  }
+
+  HistogramImpl newHistogramImpl(String name) {
+    return new HistogramImpl(name, registry.histogram(name));
+  }
+
   @Override
   public <V> CallbackMetric0<V> newCallbackMetric(
       String name, Class<V> valueClass, Description desc) {
@@ -339,4 +393,25 @@ public class DropWizardMetricMaker extends MetricMaker {
       registry.remove(name);
     }
   }
+
+  class HistogramImpl extends Histogram0 {
+    private final String name;
+    final com.codahale.metrics.Histogram metric;
+
+    private HistogramImpl(String name, com.codahale.metrics.Histogram metric) {
+      this.name = name;
+      this.metric = metric;
+    }
+
+    @Override
+    public void record(long value) {
+      metric.update(value);
+    }
+
+    @Override
+    public void remove() {
+      descriptions.remove(name);
+      registry.remove(name);
+    }
+  }
 }

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/HistogramImpl1.java

@@ -0,0 +1,52 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics.dropwizard;
+
+import com.google.common.base.Function;
+import com.google.gerrit.metrics.Description;
+import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram1;
+
+/** Optimized version of {@link BucketedHistogram} for single dimension. */
+class HistogramImpl1<F1> extends BucketedHistogram implements BucketedMetric {
+  HistogramImpl1(DropWizardMetricMaker metrics, String name,
+      Description desc, Field<F1> field1) {
+    super(metrics, name, desc, field1);
+  }
+
+  Histogram1<F1> histogram1() {
+    return new Histogram1<F1>() {
+      @Override
+      public void record(F1 field1, long value) {
+        total.record(value);
+        forceCreate(field1).record(value);
+      }
+
+      @Override
+      public void remove() {
+        doRemove();
+      }
+    };
+  }
+
+  @Override
+  String name(Object field1) {
+    @SuppressWarnings("unchecked")
+    Function<Object, String> fmt =
+        (Function<Object, String>) fields[0].formatter();
+
+    return fmt.apply(field1).replace('/', '-');
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/HistogramImplN.java

@@ -0,0 +1,75 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.metrics.dropwizard;
+
+import com.google.common.base.Function;
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.metrics.Description;
+import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram2;
+import com.google.gerrit.metrics.Histogram3;
+
+/** Generalized implementation of N-dimensional Histogram metrics. */
+class HistogramImplN extends BucketedHistogram implements BucketedMetric {
+  HistogramImplN(DropWizardMetricMaker metrics, String name,
+      Description desc, Field<?>... fields) {
+    super(metrics, name, desc, fields);
+  }
+
+  <F1, F2> Histogram2<F1, F2> histogram2() {
+    return new Histogram2<F1, F2>() {
+      @Override
+      public void record(F1 field1, F2 field2, long value) {
+        total.record(value);
+        forceCreate(field1, field2).record(value);
+      }
+
+      @Override
+      public void remove() {
+        doRemove();
+      }
+    };
+  }
+
+  <F1, F2, F3> Histogram3<F1, F2, F3> histogram3() {
+    return new Histogram3<F1, F2, F3>() {
+      @Override
+      public void record(F1 field1, F2 field2, F3 field3, long value) {
+        total.record(value);
+        forceCreate(field1, field2, field3).record(value);
+      }
+
+      @Override
+      public void remove() {
+        doRemove();
+      }
+    };
+  }
+
+  @SuppressWarnings("unchecked")
+  @Override
+  String name(Object key) {
+    ImmutableList<Object> keyList = (ImmutableList<Object>) key;
+    String[] parts = new String[fields.length];
+    for (int i = 0; i < fields.length; i++) {
+      Function<Object, String> fmt =
+          (Function<Object, String>) fields[i].formatter();
+
+      parts[i] = fmt.apply(keyList.get(i)).replace('/', '-');
+    }
+    return Joiner.on('/').join(parts);
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/MetricJson.java

@@ -22,6 +22,7 @@ import com.google.gerrit.metrics.Field;
 
 import com.codahale.metrics.Counter;
 import com.codahale.metrics.Gauge;
+import com.codahale.metrics.Histogram;
 import com.codahale.metrics.Meter;
 import com.codahale.metrics.Metric;
 import com.codahale.metrics.Snapshot;
@@ -56,7 +57,9 @@ class MetricJson {
   Double p99_9;
 
   Double min;
+  Double avg;
   Double max;
+  Double sum;
   Double std_dev;
 
   List<FieldJson> fields;
@@ -123,6 +126,24 @@ class MetricJson {
       min = s.getMin() / div;
       max = s.getMax() / div;
       std_dev = s.getStdDev() / div;
+
+    } else if (metric instanceof Histogram) {
+      Histogram m = (Histogram) metric;
+      Snapshot s = m.getSnapshot();
+      count = m.getCount();
+
+      p50 = s.getMedian();
+      p75 = s.get75thPercentile();
+      p95 = s.get95thPercentile();
+      p98 = s.get98thPercentile();
+      p99 = s.get99thPercentile();
+      p99_9 = s.get999thPercentile();
+
+      min = (double) s.getMin();
+      avg = (double) s.getMean();
+      max = (double) s.getMax();
+      sum = s.getMean() * m.getCount();
+      std_dev = s.getStdDev();
     }
   }
 

gerrit-server/src/main/java/com/google/gerrit/server/git/UploadPackMetricsHook.java

@@ -20,6 +20,7 @@ import com.google.gerrit.metrics.Counter1;
 import com.google.gerrit.metrics.Description;
 import com.google.gerrit.metrics.Description.Units;
 import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram1;
 import com.google.gerrit.metrics.MetricMaker;
 import com.google.gerrit.metrics.Timer1;
 import com.google.inject.Inject;
@@ -39,6 +40,7 @@ public class UploadPackMetricsHook implements PostUploadHook {
   private final Timer1<Operation> counting;
   private final Timer1<Operation> compressing;
   private final Timer1<Operation> writing;
+  private final Histogram1<Operation> packBytes;
 
   @Inject
   UploadPackMetricsHook(MetricMaker metricMaker) {
@@ -70,6 +72,13 @@ public class UploadPackMetricsHook implements PostUploadHook {
           .setCumulative()
           .setUnit(Units.MILLISECONDS),
         operation);
+
+    packBytes = metricMaker.newHistogram(
+        "git/upload-pack/pack_bytes",
+        new Description("Distribution of sizes of packs sent to clients")
+          .setCumulative()
+          .setUnit(Units.BYTES),
+        operation);
   }
 
   @Override
@@ -84,5 +93,6 @@ public class UploadPackMetricsHook implements PostUploadHook {
     counting.record(op, stats.getTimeCounting(), MILLISECONDS);
     compressing.record(op, stats.getTimeCompressing(), MILLISECONDS);
     writing.record(op, stats.getTimeWriting(), MILLISECONDS);
+    packBytes.record(op, stats.getTotalBytes());
   }
 }

gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginMetricMaker.java

@@ -25,6 +25,10 @@ import com.google.gerrit.metrics.Counter2;
 import com.google.gerrit.metrics.Counter3;
 import com.google.gerrit.metrics.Description;
 import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.Histogram0;
+import com.google.gerrit.metrics.Histogram1;
+import com.google.gerrit.metrics.Histogram2;
+import com.google.gerrit.metrics.Histogram3;
 import com.google.gerrit.metrics.MetricMaker;
 import com.google.gerrit.metrics.Timer0;
 import com.google.gerrit.metrics.Timer1;
@@ -117,6 +121,41 @@ class PluginMetricMaker extends MetricMaker implements LifecycleListener {
     return m;
   }
 
+  @Override
+  public Histogram0 newHistogram(String name, Description desc) {
+    Histogram0 m = root.newHistogram(prefix + name, desc);
+    cleanup.add(m);
+    return m;
+  }
+
+  @Override
+  public <F1> Histogram1<F1> newHistogram(
+      String name, Description desc,
+      Field<F1> field1) {
+    Histogram1<F1> m = root.newHistogram(prefix + name, desc, field1);
+    cleanup.add(m);
+    return m;
+  }
+
+  @Override
+  public <F1, F2> Histogram2<F1, F2> newHistogram(
+      String name, Description desc,
+      Field<F1> field1, Field<F2> field2) {
+    Histogram2<F1, F2> m = root.newHistogram(prefix + name, desc, field1, field2);
+    cleanup.add(m);
+    return m;
+  }
+
+  @Override
+  public <F1, F2, F3> Histogram3<F1, F2, F3> newHistogram(
+      String name, Description desc,
+      Field<F1> field1, Field<F2> field2, Field<F3> field3) {
+    Histogram3<F1, F2, F3> m =
+        root.newHistogram(prefix + name, desc, field1, field2, field3);
+    cleanup.add(m);
+    return m;
+  }
+
   @Override
   public <V> CallbackMetric0<V> newCallbackMetric(
       String name, Class<V> valueClass, Description desc) {