diff --git a/Documentation/dev-plugins.txt b/Documentation/dev-plugins.txt
index 82a9527..e84effd 100644
--- a/Documentation/dev-plugins.txt
+++ b/Documentation/dev-plugins.txt
@@ -2670,6 +2670,94 @@
 are met, but marked as `OK`. If the requirements were not displayed, reviewers
 would need to use their precious time to manually check that they were met.
 
+[[quota-enforcer]]
+== Quota Enforcer
+
+Gerrit provides an extension point that allows a plugin to enforce quota.
+link:quota.html[This documentation page] has a list of all quota requests that
+Gerrit core issues. Plugins can choose to respond to all or just a subset of
+requests. Some implementations might want to keep track of user quota in buckets,
+others might just check against instance or project state to enforce limits on how
+many projects can be created or how large a repository can become.
+
+Checking against instance state can be racy for concurrent requests as the server does not
+refill tokens if the action fails in a later stage (e.g. database failure). If
+plugins want to guarantee an absolute maximum on a resource, they have to do their own
+book-keeping.
+
+[source, java]
+----
+import com.google.server.quota.QuotaEnforcer;
+
+class ProjectLimiter implements QuotaEnforcer {
+  private final long maxNumberOfProjects = 100;
+  @Override
+  QuotaResponse requestTokens(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    if (!"/projects/create".equals(quotaGroup)) {
+      return QuotaResponse.noOp();
+    }
+    // No deduction because we always check against the instance state (racy but fine for
+    // this plugin)
+    if (currentNumberOfProjects() + numTokens > maxNumberOfProjects) {
+      return QuotaResponse.error("too many projects");
+    }
+    return QuotaResponse.ok();
+  }
+
+  @Override
+  QuotaResponse dryRun(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    // Since we are not keeping any state in this enforcer, we can simply call requestTokens().
+    return requestTokens(quotaGroup, ctx, numTokens);
+  }
+
+  void refill(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    // No-op
+  }
+}
+----
+
+[source, java]
+----
+import com.google.server.quota.QuotaEnforcer;
+
+class ApiQpsEnforcer implements QuotaEnforcer {
+  // AutoRefillingPerUserBuckets is a imaginary bucket implementation that could be based on
+  // a loading cache or a commonly used bucketing algorithm.
+  private final AutoRefillingPerUserBuckets<CurrentUser, Long> buckets;
+  @Override
+  QuotaResponse requestTokens(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    if (!quotaGroup.startsWith("/restapi/")) {
+      return QuotaResponse.noOp();
+    }
+    boolean success = buckets.deduct(ctx.user(), numTokens);
+    if (!success) {
+      return QuotaResponse.error("user sent too many qps, please wait for 5 minutes");
+    }
+    return QuotaResponse.ok();
+  }
+
+  @Override
+  QuotaResponse dryRun(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    if (!quotaGroup.startsWith("/restapi/")) {
+      return QuotaResponse.noOp();
+    }
+    boolean success = buckets.checkOnly(ctx.user(), numTokens);
+    if (!success) {
+      return QuotaResponse.error("user sent too many qps, please wait for 5 minutes");
+    }
+    return QuotaResponse.ok();
+  }
+
+  @Override
+  void refill(String quotaGroup, QuotaRequestContext ctx, long numTokens) {
+    if (!quotaGroup.startsWith("/restapi/")) {
+      return;
+    }
+    buckets.add(ctx.user(), numTokens);
+  }
+}
+----
+
 
 == SEE ALSO
 
diff --git a/Documentation/index.txt b/Documentation/index.txt
index 6011158..557cf90 100644
--- a/Documentation/index.txt
+++ b/Documentation/index.txt
@@ -85,6 +85,7 @@
 .. link:js-api.html[JavaScript Plugin API]
 .. link:config-validation.html[Validation Interfaces]
 .. link:dev-stars.html[Starring Changes]
+.. link:quota.html[Quota Enforcement]
 . link:dev-design.html[System Design]
 . link:i18n-readme.html[i18n Support]
 
diff --git a/Documentation/quota.txt b/Documentation/quota.txt
new file mode 100644
index 0000000..a647e33
--- /dev/null
+++ b/Documentation/quota.txt
@@ -0,0 +1,50 @@
+= Gerrit Code Review - Quota
+
+Gerrit does not provide out of the box quota enforcement. However, it does
+support an extension mechanism for plugins to hook into to provide this
+functionality. The most prominent plugin is the
+link:https://gerrit.googlesource.com/plugins/quota/[Quota Plugin].
+
+This documentation is intended to be read by plugin developers. It contains all
+quota requests implemented in Gerrit-core as well as the metadata that they have
+associated.
+
+== Quota Groups
+
+The following quota groups are defined in core Gerrit:
+
+=== REST API
+[[rest-api]]
+
+The REST API enforces quota after the resource was parsed (if applicable) and before the
+endpoint's logic is executed. This enables quota enforcer implementations to throttle calls
+to specific endpoints while knowing the general context (user and top-level entity such as
+change, project or account).
+
+If the quota enforcer wants to throttle HTTP requests, they should use
+link:quota.html#http-requests[HTTP Requests] instead.
+
+The quota groups used for checking follow the exact definition of the endoint in the REST
+API, but remove all IDs. The schema is:
+
+/restapi/<ENDPOINT>:<HTTP-METHOD>
+
+Examples:
+
+[options="header",cols="1,6"]
+|=======================
+|HTTP call                                 |Quota Group                    |Metadata
+|GET /a/changes/1/revisions/current/detail |/changes/revisions/detail:GET  |CurrentUser, Change.Id, Project.NameKey
+|POST /a/changes/                          |/changes/:POST                 |CurrentUser
+|GET /a/accounts/self/detail               |/accounts/detail:GET           |CurrentUser, Account.Id
+|=======================
+
+The user provided in the check's metadata is always the calling user (having the
+impersonation bit and real user set in case the user is impersonating another user).
+
+GERRIT
+------
+Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------
diff --git a/Documentation/rest-api.txt b/Documentation/rest-api.txt
index 8f6a47b..a8ab353 100644
--- a/Documentation/rest-api.txt
+++ b/Documentation/rest-api.txt
@@ -191,6 +191,11 @@
 "`422 Unprocessable Entity`" is returned if the ID of a resource that is
 specified in the request body cannot be resolved.
 
+==== 429 Too Many Requests
+"`429 Too Many Requests`" is returned if the request exhausted any set
+quota limits. Depending on the exhausted quota, the request may be retried
+with exponential backoff.
+
 [[tracing]]
 === Request Tracing
 For each REST endpoint tracing can be enabled by setting the
diff --git a/java/com/google/gerrit/acceptance/BUILD b/java/com/google/gerrit/acceptance/BUILD
index b0a39cf..7becf99 100644
--- a/java/com/google/gerrit/acceptance/BUILD
+++ b/java/com/google/gerrit/acceptance/BUILD
@@ -26,6 +26,7 @@
         "//java/com/google/gerrit/pgm/util",
         "//java/com/google/gerrit/reviewdb:server",
         "//java/com/google/gerrit/server",
+        "//java/com/google/gerrit/server/audit",
         "//java/com/google/gerrit/server/git/receive",
         "//java/com/google/gerrit/server/project/testing:project-test-util",
         "//java/com/google/gerrit/server/restapi",
diff --git a/java/com/google/gerrit/httpd/GitOverHttpServlet.java b/java/com/google/gerrit/httpd/GitOverHttpServlet.java
index e74c4b2..2e1b562 100644
--- a/java/com/google/gerrit/httpd/GitOverHttpServlet.java
+++ b/java/com/google/gerrit/httpd/GitOverHttpServlet.java
@@ -15,7 +15,7 @@
 package com.google.gerrit.httpd;
 
 import com.google.common.cache.Cache;
-import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableListMultimap;
 import com.google.common.collect.ListMultimap;
 import com.google.common.collect.Lists;
 import com.google.gerrit.common.data.Capable;
@@ -52,6 +52,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
@@ -61,6 +62,7 @@
 import javax.servlet.ServletResponse;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
+import javax.servlet.http.HttpServletResponseWrapper;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.http.server.GitServlet;
 import org.eclipse.jgit.http.server.GitSmartHttpTools;
@@ -130,6 +132,55 @@
     }
   }
 
+  static class HttpServletResponseWithStatusWrapper extends HttpServletResponseWrapper {
+    private int responseStatus;
+
+    HttpServletResponseWithStatusWrapper(HttpServletResponse response) {
+      super(response);
+      /* Even if we could read the status from response, we assume that it is all
+       * fine because we entered the filter without any prior issues.
+       * When Google will have upgraded to Servlet 3.0, we could actually
+       * call response.getStatus() and the code will be clearer.
+       */
+      responseStatus = HttpServletResponse.SC_OK;
+    }
+
+    @Override
+    public void setStatus(int sc) {
+      responseStatus = sc;
+      super.setStatus(sc);
+    }
+
+    @SuppressWarnings("deprecation")
+    @Override
+    public void setStatus(int sc, String sm) {
+      responseStatus = sc;
+      super.setStatus(sc, sm);
+    }
+
+    @Override
+    public void sendError(int sc) throws IOException {
+      this.responseStatus = sc;
+      super.sendError(sc);
+    }
+
+    @Override
+    public void sendError(int sc, String msg) throws IOException {
+      this.responseStatus = sc;
+      super.sendError(sc, msg);
+    }
+
+    @Override
+    public void sendRedirect(String location) throws IOException {
+      this.responseStatus = HttpServletResponse.SC_MOVED_TEMPORARILY;
+      super.sendRedirect(location);
+    }
+
+    public int getResponseStatus() {
+      return responseStatus;
+    }
+  }
+
   @Inject
   GitOverHttpServlet(
       Resolver resolver,
@@ -156,19 +207,15 @@
   }
 
   private static ListMultimap<String, String> extractParameters(HttpServletRequest request) {
-
-    ListMultimap<String, String> multiMap = ArrayListMultimap.create();
-    if (request.getQueryString() != null) {
-      request
-          .getParameterMap()
-          .forEach(
-              (k, v) -> {
-                for (int i = 0; i < v.length; i++) {
-                  multiMap.put(k, v[i]);
-                }
-              });
+    if (request.getQueryString() == null) {
+      return ImmutableListMultimap.of();
     }
-    return multiMap;
+    // Explicit cast is required to compile under Servlet API 2.5, where the return type is raw Map.
+    @SuppressWarnings("cast")
+    Map<String, String[]> parameterMap = (Map<String, String[]>) request.getParameterMap();
+    ImmutableListMultimap.Builder<String, String> b = ImmutableListMultimap.builder();
+    parameterMap.forEach(b::putAll);
+    return b.build();
   }
 
   static class Resolver implements RepositoryResolver<HttpServletRequest> {
@@ -301,41 +348,48 @@
       UploadPack up = (UploadPack) request.getAttribute(ServletUtils.ATTRIBUTE_HANDLER);
       PermissionBackend.ForProject perm =
           permissionBackend.currentUser().project(state.getNameKey());
+      HttpServletResponseWithStatusWrapper responseWrapper =
+          new HttpServletResponseWithStatusWrapper((HttpServletResponse) response);
+      HttpServletRequest httpRequest = (HttpServletRequest) request;
+      String sessionId = httpRequest.getSession().getId();
+
       try {
-        perm.check(ProjectPermission.RUN_UPLOAD_PACK);
-      } catch (AuthException e) {
-        GitSmartHttpTools.sendError(
-            (HttpServletRequest) request,
-            (HttpServletResponse) response,
-            HttpServletResponse.SC_FORBIDDEN,
-            "upload-pack not permitted on this server");
-        return;
-      } catch (PermissionBackendException e) {
-        throw new ServletException(e);
+        try {
+          perm.check(ProjectPermission.RUN_UPLOAD_PACK);
+        } catch (AuthException e) {
+          GitSmartHttpTools.sendError(
+              (HttpServletRequest) request,
+              responseWrapper,
+              HttpServletResponse.SC_FORBIDDEN,
+              "upload-pack not permitted on this server");
+          return;
+        } catch (PermissionBackendException e) {
+          responseWrapper.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
+          throw new ServletException(e);
+        }
+
+        // We use getRemoteHost() here instead of getRemoteAddr() because REMOTE_ADDR
+        // may have been overridden by a proxy server -- we'll try to avoid this.
+        UploadValidators uploadValidators =
+            uploadValidatorsFactory.create(state.getProject(), repo, request.getRemoteHost());
+        up.setPreUploadHook(
+            PreUploadHookChain.newChain(
+                Lists.newArrayList(up.getPreUploadHook(), uploadValidators)));
+        up.setAdvertiseRefsHook(new DefaultAdvertiseRefsHook(perm, RefFilterOptions.defaults()));
+        next.doFilter(httpRequest, responseWrapper);
       } finally {
-        HttpServletRequest httpRequest = (HttpServletRequest) request;
-        HttpServletResponse httpResponse = (HttpServletResponse) response;
         groupAuditService.dispatch(
             new HttpAuditEvent(
-                httpRequest.getSession().getId(),
+                sessionId,
                 userProvider.get(),
                 extractWhat(httpRequest),
                 TimeUtil.nowMs(),
                 extractParameters(httpRequest),
                 httpRequest.getMethod(),
                 httpRequest,
-                httpResponse.getStatus(),
-                httpResponse));
+                responseWrapper.getResponseStatus(),
+                responseWrapper));
       }
-
-      // We use getRemoteHost() here instead of getRemoteAddr() because REMOTE_ADDR
-      // may have been overridden by a proxy server -- we'll try to avoid this.
-      UploadValidators uploadValidators =
-          uploadValidatorsFactory.create(state.getProject(), repo, request.getRemoteHost());
-      up.setPreUploadHook(
-          PreUploadHookChain.newChain(Lists.newArrayList(up.getPreUploadHook(), uploadValidators)));
-      up.setAdvertiseRefsHook(new DefaultAdvertiseRefsHook(perm, RefFilterOptions.defaults()));
-      next.doFilter(request, response);
     }
 
     @Override
@@ -411,25 +465,28 @@
       rp.getAdvertiseRefsHook().advertiseRefs(rp);
 
       ProjectState state = (ProjectState) request.getAttribute(ATT_STATE);
+      HttpServletResponseWithStatusWrapper responseWrapper =
+          new HttpServletResponseWithStatusWrapper((HttpServletResponse) response);
+      HttpServletRequest httpRequest = (HttpServletRequest) request;
       Capable canUpload;
       try {
-        permissionBackend
-            .currentUser()
-            .project(state.getNameKey())
-            .check(ProjectPermission.RUN_RECEIVE_PACK);
-        canUpload = arc.canUpload();
-      } catch (AuthException e) {
-        GitSmartHttpTools.sendError(
-            (HttpServletRequest) request,
-            (HttpServletResponse) response,
-            HttpServletResponse.SC_FORBIDDEN,
-            "receive-pack not permitted on this server");
-        return;
-      } catch (PermissionBackendException e) {
-        throw new RuntimeException(e);
+        try {
+          permissionBackend
+              .currentUser()
+              .project(state.getNameKey())
+              .check(ProjectPermission.RUN_RECEIVE_PACK);
+          canUpload = arc.canUpload();
+        } catch (AuthException e) {
+          GitSmartHttpTools.sendError(
+              httpRequest,
+              responseWrapper,
+              HttpServletResponse.SC_FORBIDDEN,
+              "receive-pack not permitted on this server");
+          return;
+        } catch (PermissionBackendException e) {
+          throw new RuntimeException(e);
+        }
       } finally {
-        HttpServletRequest httpRequest = (HttpServletRequest) request;
-        HttpServletResponse httpResponse = (HttpServletResponse) response;
         groupAuditService.dispatch(
             new HttpAuditEvent(
                 httpRequest.getSession().getId(),
@@ -439,26 +496,26 @@
                 extractParameters(httpRequest),
                 httpRequest.getMethod(),
                 httpRequest,
-                httpResponse.getStatus(),
-                httpResponse));
+                responseWrapper.getResponseStatus(),
+                responseWrapper));
       }
 
       if (canUpload != Capable.OK) {
         GitSmartHttpTools.sendError(
-            (HttpServletRequest) request,
-            (HttpServletResponse) response,
+            httpRequest,
+            responseWrapper,
             HttpServletResponse.SC_FORBIDDEN,
             "\n" + canUpload.getMessage());
         return;
       }
 
       if (!rp.isCheckReferencedObjectsAreReachable()) {
-        chain.doFilter(request, response);
+        chain.doFilter(request, responseWrapper);
         return;
       }
 
       if (!(userProvider.get().isIdentifiedUser())) {
-        chain.doFilter(request, response);
+        chain.doFilter(request, responseWrapper);
         return;
       }
 
@@ -475,7 +532,7 @@
         }
       }
 
-      chain.doFilter(request, response);
+      chain.doFilter(request, responseWrapper);
 
       if (isGet) {
         cache.put(cacheKey, Collections.unmodifiableSet(new HashSet<>(rp.getAdvertisedObjects())));
diff --git a/java/com/google/gerrit/httpd/restapi/RestApiQuotaEnforcer.java b/java/com/google/gerrit/httpd/restapi/RestApiQuotaEnforcer.java
new file mode 100644
index 0000000..c7678c2
--- /dev/null
+++ b/java/com/google/gerrit/httpd/restapi/RestApiQuotaEnforcer.java
@@ -0,0 +1,83 @@
+// Copyright (C) 2018 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.httpd.restapi;
+
+import com.google.gerrit.extensions.restapi.RestResource;
+import com.google.gerrit.server.account.AccountResource;
+import com.google.gerrit.server.change.ChangeResource;
+import com.google.gerrit.server.project.ProjectResource;
+import com.google.gerrit.server.quota.QuotaBackend;
+import com.google.gerrit.server.quota.QuotaException;
+import com.google.gerrit.util.http.RequestUtil;
+import javax.inject.Inject;
+import javax.servlet.http.HttpServletRequest;
+
+/**
+ * Enforces quota on specific REST API endpoints.
+ *
+ * <p>Examples:
+ *
+ * <ul>
+ *   <li>GET /a/accounts/self/detail => /restapi/accounts/detail:GET
+ *   <li>GET /changes/123/revisions/current/detail => /restapi/changes/revisions/detail:GET
+ *   <li>PUT /changes/10/reviewed => /changes/reviewed:PUT
+ * </ul>
+ *
+ * <p>Adds context (change, project, account) to the quota check if the call is for an existing
+ * entity that was successfully parsed. This quota check is generally enforced after the resource
+ * was parsed, but before the view is executed. If a quota enforcer desires to throttle earlier,
+ * they should consider quota groups in the {@code /http/*} space.
+ */
+public class RestApiQuotaEnforcer {
+  private final QuotaBackend quotaBackend;
+
+  @Inject
+  RestApiQuotaEnforcer(QuotaBackend quotaBackend) {
+    this.quotaBackend = quotaBackend;
+  }
+
+  /** Enforce quota on a request not tied to any {@code RestResource}. */
+  void enforce(HttpServletRequest req) throws QuotaException {
+    String pathForQuotaReporting = RequestUtil.getRestPathWithoutIds(req);
+    quotaBackend
+        .currentUser()
+        .requestToken(quotaGroup(pathForQuotaReporting, req.getMethod()))
+        .throwOnError();
+  }
+
+  /** Enforce quota on a request for a given resource. */
+  void enforce(RestResource rsrc, HttpServletRequest req) throws QuotaException {
+    String pathForQuotaReporting = RequestUtil.getRestPathWithoutIds(req);
+    // Enrich the quota request we are operating on an interesting collection
+    QuotaBackend.WithResource report = quotaBackend.currentUser();
+    if (rsrc instanceof ChangeResource) {
+      ChangeResource changeResource = (ChangeResource) rsrc;
+      report =
+          quotaBackend.currentUser().change(changeResource.getId(), changeResource.getProject());
+    } else if (rsrc instanceof AccountResource) {
+      AccountResource accountResource = (AccountResource) rsrc;
+      report = quotaBackend.currentUser().account(accountResource.getUser().getAccountId());
+    } else if (rsrc instanceof ProjectResource) {
+      ProjectResource accountResource = (ProjectResource) rsrc;
+      report = quotaBackend.currentUser().account(accountResource.getUser().getAccountId());
+    }
+
+    report.requestToken(quotaGroup(pathForQuotaReporting, req.getMethod())).throwOnError();
+  }
+
+  private static String quotaGroup(String path, String method) {
+    return "/restapi" + path + ":" + method;
+  }
+}
diff --git a/java/com/google/gerrit/httpd/restapi/RestApiServlet.java b/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
index ec71d8f..c9f3a77 100644
--- a/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
+++ b/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
@@ -114,6 +114,7 @@
 import com.google.gerrit.server.permissions.GlobalPermission;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
+import com.google.gerrit.server.quota.QuotaException;
 import com.google.gerrit.server.update.UpdateException;
 import com.google.gerrit.server.util.time.TimeUtil;
 import com.google.gerrit.util.http.CacheHeaders;
@@ -227,6 +228,7 @@
     final AuditService auditService;
     final RestApiMetrics metrics;
     final Pattern allowOrigin;
+    final RestApiQuotaEnforcer quotaChecker;
 
     @Inject
     Globals(
@@ -236,6 +238,7 @@
         PermissionBackend permissionBackend,
         AuditService auditService,
         RestApiMetrics metrics,
+        RestApiQuotaEnforcer quotaChecker,
         @GerritServerConfig Config cfg) {
       this.currentUser = currentUser;
       this.webSession = webSession;
@@ -243,6 +246,7 @@
       this.permissionBackend = permissionBackend;
       this.auditService = auditService;
       this.metrics = metrics;
+      this.quotaChecker = quotaChecker;
       allowOrigin = makeAllowOrigin(cfg);
     }
 
@@ -317,6 +321,7 @@
         viewData = new ViewData(null, null);
 
         if (path.isEmpty()) {
+          globals.quotaChecker.enforce(req);
           if (rc instanceof NeedsParams) {
             ((NeedsParams) rc).setParams(qp.params());
           }
@@ -339,6 +344,7 @@
           IdString id = path.remove(0);
           try {
             rsrc = rc.parse(rsrc, id);
+            globals.quotaChecker.enforce(rsrc, req);
             if (path.isEmpty()) {
               checkPreconditions(req);
             }
@@ -346,6 +352,7 @@
             if (!path.isEmpty()) {
               throw e;
             }
+            globals.quotaChecker.enforce(req);
 
             if (isPost(req) || isPut(req)) {
               RestView<RestResource> createView = rc.views().get(PluginName.GERRIT, "CREATE./");
@@ -602,6 +609,9 @@
           status = SC_INTERNAL_SERVER_ERROR;
           responseBytes = handleException(e, req, res);
         }
+      } catch (QuotaException e) {
+        responseBytes =
+            replyError(req, res, status = 429, messageOr(e, "Quota limit reached"), e.caching(), e);
       } catch (Exception e) {
         status = SC_INTERNAL_SERVER_ERROR;
         responseBytes = handleException(e, req, res);
diff --git a/java/com/google/gerrit/pgm/init/GroupsOnInit.java b/java/com/google/gerrit/pgm/init/GroupsOnInit.java
index 8e06aa1..584d8af 100644
--- a/java/com/google/gerrit/pgm/init/GroupsOnInit.java
+++ b/java/com/google/gerrit/pgm/init/GroupsOnInit.java
@@ -25,7 +25,6 @@
 import com.google.gerrit.pgm.init.api.InitFlags;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
-import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.GerritPersonIdentProvider;
 import com.google.gerrit.server.config.AllUsersName;
 import com.google.gerrit.server.config.GerritServerIdProvider;
@@ -37,7 +36,6 @@
 import com.google.gerrit.server.group.db.GroupConfig;
 import com.google.gerrit.server.group.db.GroupNameNotes;
 import com.google.gerrit.server.group.db.InternalGroupUpdate;
-import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
 import java.io.File;
 import java.io.IOException;
@@ -54,9 +52,8 @@
 /**
  * A database accessor for calls related to groups.
  *
- * <p>All calls which read or write group related details to the database <strong>during
- * init</strong> (either ReviewDb or NoteDb) are gathered here. For non-init cases, use {@code
- * Groups} or {@code GroupsUpdate} instead.
+ * <p>All calls which read or write group related details to the NoteDb <strong>during init</strong>
+ * are gathered here. For non-init cases, use {@code Groups} or {@code GroupsUpdate} instead.
  *
  * <p>All methods of this class refer to <em>internal</em> groups.
  */
@@ -76,16 +73,14 @@
   /**
    * Returns the {@code AccountGroup} for the specified {@code GroupReference}.
    *
-   * @param db the {@code ReviewDb} instance to use for lookups
    * @param groupReference the {@code GroupReference} of the group
    * @return the {@code InternalGroup} represented by the {@code GroupReference}
-   * @throws OrmException if the group couldn't be retrieved from ReviewDb
    * @throws IOException if an error occurs while reading from NoteDb
    * @throws ConfigInvalidException if the data in NoteDb is in an incorrect format
    * @throws NoSuchGroupException if a group with such a name doesn't exist
    */
-  public InternalGroup getExistingGroup(ReviewDb db, GroupReference groupReference)
-      throws OrmException, NoSuchGroupException, IOException, ConfigInvalidException {
+  public InternalGroup getExistingGroup(GroupReference groupReference)
+      throws NoSuchGroupException, IOException, ConfigInvalidException {
     File allUsersRepoPath = getPathToAllUsersRepository();
     if (allUsersRepoPath != null) {
       try (Repository allUsersRepo = new FileRepository(allUsersRepoPath)) {
@@ -102,14 +97,11 @@
   /**
    * Returns {@code GroupReference}s for all internal groups.
    *
-   * @param db the {@code ReviewDb} instance to use for lookups
    * @return a stream of the {@code GroupReference}s of all internal groups
-   * @throws OrmException if an error occurs while reading from ReviewDb
    * @throws IOException if an error occurs while reading from NoteDb
    * @throws ConfigInvalidException if the data in NoteDb is in an incorrect format
    */
-  public Stream<GroupReference> getAllGroupReferences(ReviewDb db)
-      throws OrmException, IOException, ConfigInvalidException {
+  public Stream<GroupReference> getAllGroupReferences() throws IOException, ConfigInvalidException {
     File allUsersRepoPath = getPathToAllUsersRepository();
     if (allUsersRepoPath != null) {
       try (Repository allUsersRepo = new FileRepository(allUsersRepoPath)) {
@@ -126,14 +118,12 @@
    * <p><strong>Note</strong>: This method doesn't check whether the account exists! It also doesn't
    * update the account index!
    *
-   * @param db the {@code ReviewDb} instance to update
    * @param groupUuid the UUID of the group
    * @param account the account to add
-   * @throws OrmException if an error occurs while reading/writing from/to ReviewDb
    * @throws NoSuchGroupException if the specified group doesn't exist
    */
-  public void addGroupMember(ReviewDb db, AccountGroup.UUID groupUuid, Account account)
-      throws OrmException, NoSuchGroupException, IOException, ConfigInvalidException {
+  public void addGroupMember(AccountGroup.UUID groupUuid, Account account)
+      throws NoSuchGroupException, IOException, ConfigInvalidException {
     File allUsersRepoPath = getPathToAllUsersRepository();
     if (allUsersRepoPath != null) {
       try (Repository repository = new FileRepository(allUsersRepoPath)) {
diff --git a/java/com/google/gerrit/pgm/init/InitAdminUser.java b/java/com/google/gerrit/pgm/init/InitAdminUser.java
index f12fa50..f19cf39 100644
--- a/java/com/google/gerrit/pgm/init/InitAdminUser.java
+++ b/java/com/google/gerrit/pgm/init/InitAdminUser.java
@@ -26,7 +26,6 @@
 import com.google.gerrit.pgm.init.api.InitStep;
 import com.google.gerrit.pgm.init.api.SequencesOnInit;
 import com.google.gerrit.reviewdb.client.Account;
-import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.account.AccountSshKey;
 import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.account.externalids.ExternalId;
@@ -37,7 +36,6 @@
 import com.google.gerrit.server.index.group.GroupIndex;
 import com.google.gerrit.server.index.group.GroupIndexCollection;
 import com.google.gerrit.server.util.time.TimeUtil;
-import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
 import java.io.IOException;
 import java.nio.file.Files;
@@ -57,7 +55,6 @@
   private final ExternalIdsOnInit externalIds;
   private final SequencesOnInit sequencesOnInit;
   private final GroupsOnInit groupsOnInit;
-  private SchemaFactory<ReviewDb> dbFactory;
   private AccountIndexCollection accountIndexCollection;
   private GroupIndexCollection groupIndexCollection;
 
@@ -84,11 +81,6 @@
   @Override
   public void run() {}
 
-  @Inject(optional = true)
-  void set(SchemaFactory<ReviewDb> dbFactory) {
-    this.dbFactory = dbFactory;
-  }
-
   @Inject
   void set(AccountIndexCollection accountIndexCollection) {
     this.accountIndexCollection = accountIndexCollection;
@@ -106,58 +98,56 @@
       return;
     }
 
-    try (ReviewDb db = dbFactory.open()) {
-      if (!accounts.hasAnyAccount()) {
-        ui.header("Gerrit Administrator");
-        if (ui.yesno(true, "Create administrator user")) {
-          Account.Id id = new Account.Id(sequencesOnInit.nextAccountId(db));
-          String username = ui.readString("admin", "username");
-          String name = ui.readString("Administrator", "name");
-          String httpPassword = ui.readString("secret", "HTTP password");
-          AccountSshKey sshKey = readSshKey(id);
-          String email = readEmail(sshKey);
+    if (!accounts.hasAnyAccount()) {
+      ui.header("Gerrit Administrator");
+      if (ui.yesno(true, "Create administrator user")) {
+        Account.Id id = new Account.Id(sequencesOnInit.nextAccountId());
+        String username = ui.readString("admin", "username");
+        String name = ui.readString("Administrator", "name");
+        String httpPassword = ui.readString("secret", "HTTP password");
+        AccountSshKey sshKey = readSshKey(id);
+        String email = readEmail(sshKey);
 
-          List<ExternalId> extIds = new ArrayList<>(2);
-          extIds.add(ExternalId.createUsername(username, id, httpPassword));
+        List<ExternalId> extIds = new ArrayList<>(2);
+        extIds.add(ExternalId.createUsername(username, id, httpPassword));
 
-          if (email != null) {
-            extIds.add(ExternalId.createEmail(id, email));
-          }
-          externalIds.insert("Add external IDs for initial admin user", extIds);
+        if (email != null) {
+          extIds.add(ExternalId.createEmail(id, email));
+        }
+        externalIds.insert("Add external IDs for initial admin user", extIds);
 
-          Account a = new Account(id, TimeUtil.nowTs());
-          a.setFullName(name);
-          a.setPreferredEmail(email);
-          accounts.insert(a);
+        Account a = new Account(id, TimeUtil.nowTs());
+        a.setFullName(name);
+        a.setPreferredEmail(email);
+        accounts.insert(a);
 
-          // Only two groups should exist at this point in time and hence iterating over all of them
-          // is cheap.
-          Optional<GroupReference> adminGroupReference =
-              groupsOnInit
-                  .getAllGroupReferences(db)
-                  .filter(group -> group.getName().equals("Administrators"))
-                  .findAny();
-          if (!adminGroupReference.isPresent()) {
-            throw new NoSuchGroupException("Administrators");
-          }
-          GroupReference adminGroup = adminGroupReference.get();
-          groupsOnInit.addGroupMember(db, adminGroup.getUUID(), a);
+        // Only two groups should exist at this point in time and hence iterating over all of them
+        // is cheap.
+        Optional<GroupReference> adminGroupReference =
+            groupsOnInit
+                .getAllGroupReferences()
+                .filter(group -> group.getName().equals("Administrators"))
+                .findAny();
+        if (!adminGroupReference.isPresent()) {
+          throw new NoSuchGroupException("Administrators");
+        }
+        GroupReference adminGroup = adminGroupReference.get();
+        groupsOnInit.addGroupMember(adminGroup.getUUID(), a);
 
-          if (sshKey != null) {
-            VersionedAuthorizedKeysOnInit authorizedKeys = authorizedKeysFactory.create(id).load();
-            authorizedKeys.addKey(sshKey.sshPublicKey());
-            authorizedKeys.save("Add SSH key for initial admin user\n");
-          }
+        if (sshKey != null) {
+          VersionedAuthorizedKeysOnInit authorizedKeys = authorizedKeysFactory.create(id).load();
+          authorizedKeys.addKey(sshKey.sshPublicKey());
+          authorizedKeys.save("Add SSH key for initial admin user\n");
+        }
 
-          AccountState as = AccountState.forAccount(new AllUsersName(allUsers.get()), a, extIds);
-          for (AccountIndex accountIndex : accountIndexCollection.getWriteIndexes()) {
-            accountIndex.replace(as);
-          }
+        AccountState as = AccountState.forAccount(new AllUsersName(allUsers.get()), a, extIds);
+        for (AccountIndex accountIndex : accountIndexCollection.getWriteIndexes()) {
+          accountIndex.replace(as);
+        }
 
-          InternalGroup adminInternalGroup = groupsOnInit.getExistingGroup(db, adminGroup);
-          for (GroupIndex groupIndex : groupIndexCollection.getWriteIndexes()) {
-            groupIndex.replace(adminInternalGroup);
-          }
+        InternalGroup adminInternalGroup = groupsOnInit.getExistingGroup(adminGroup);
+        for (GroupIndex groupIndex : groupIndexCollection.getWriteIndexes()) {
+          groupIndex.replace(adminInternalGroup);
         }
       }
     }
diff --git a/java/com/google/gerrit/pgm/init/api/SequencesOnInit.java b/java/com/google/gerrit/pgm/init/api/SequencesOnInit.java
index c9c3a64..1716a3c 100644
--- a/java/com/google/gerrit/pgm/init/api/SequencesOnInit.java
+++ b/java/com/google/gerrit/pgm/init/api/SequencesOnInit.java
@@ -35,16 +35,14 @@
     this.allUsersName = allUsersName;
   }
 
-  public int nextAccountId(ReviewDb db) throws OrmException {
-    @SuppressWarnings("deprecation")
-    RepoSequence.Seed accountSeed = db::nextAccountId;
+  public int nextAccountId() throws OrmException {
     RepoSequence accountSeq =
         new RepoSequence(
             repoManager,
             GitReferenceUpdated.DISABLED,
             new Project.NameKey(allUsersName.get()),
             Sequences.NAME_ACCOUNTS,
-            accountSeed,
+            () -> ReviewDb.FIRST_ACCOUNT_ID,
             1);
     return accountSeq.next();
   }
diff --git a/java/com/google/gerrit/reviewdb/server/ReviewDb.java b/java/com/google/gerrit/reviewdb/server/ReviewDb.java
index 8e4292c..90cd066 100644
--- a/java/com/google/gerrit/reviewdb/server/ReviewDb.java
+++ b/java/com/google/gerrit/reviewdb/server/ReviewDb.java
@@ -14,8 +14,6 @@
 
 package com.google.gerrit.reviewdb.server;
 
-import com.google.gerrit.reviewdb.client.Account;
-import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.Relation;
@@ -28,7 +26,6 @@
  * <p>Root entities that are at the top level of some important data graph:
  *
  * <ul>
- *   <li>{@link Account}: Per-user account registration, preferences, identity.
  *   <li>{@link Change}: All review information about a single proposed change.
  * </ul>
  */
@@ -91,22 +88,8 @@
 
   int FIRST_ACCOUNT_ID = 1000000;
 
-  /**
-   * Next unique id for a {@link Account}.
-   *
-   * @deprecated use {@link com.google.gerrit.server.Sequences#nextAccountId()}.
-   */
-  @Sequence(startWith = FIRST_ACCOUNT_ID)
-  @Deprecated
-  int nextAccountId() throws OrmException;
-
   int FIRST_GROUP_ID = 1;
 
-  /** Next unique id for a {@link AccountGroup}. */
-  @Sequence(startWith = FIRST_GROUP_ID)
-  @Deprecated
-  int nextAccountGroupId() throws OrmException;
-
   int FIRST_CHANGE_ID = 1;
 
   /**
diff --git a/java/com/google/gerrit/reviewdb/server/ReviewDbWrapper.java b/java/com/google/gerrit/reviewdb/server/ReviewDbWrapper.java
index 202729e..c420254 100644
--- a/java/com/google/gerrit/reviewdb/server/ReviewDbWrapper.java
+++ b/java/com/google/gerrit/reviewdb/server/ReviewDbWrapper.java
@@ -136,18 +136,6 @@
 
   @Override
   @SuppressWarnings("deprecation")
-  public int nextAccountId() throws OrmException {
-    return delegate.nextAccountId();
-  }
-
-  @Override
-  @SuppressWarnings("deprecation")
-  public int nextAccountGroupId() throws OrmException {
-    return delegate.nextAccountGroupId();
-  }
-
-  @Override
-  @SuppressWarnings("deprecation")
   public int nextChangeId() throws OrmException {
     return delegate.nextChangeId();
   }
diff --git a/java/com/google/gerrit/server/Sequences.java b/java/com/google/gerrit/server/Sequences.java
index fcf0759..70a02a8 100644
--- a/java/com/google/gerrit/server/Sequences.java
+++ b/java/com/google/gerrit/server/Sequences.java
@@ -93,11 +93,15 @@
         new RepoSequence(
             repoManager, gitRefUpdated, allProjects, NAME_CHANGES, changeSeed, changeBatchSize);
 
-    RepoSequence.Seed groupSeed = () -> nextGroupId(db.get());
     int groupBatchSize = 1;
     groupSeq =
         new RepoSequence(
-            repoManager, gitRefUpdated, allUsers, NAME_GROUPS, groupSeed, groupBatchSize);
+            repoManager,
+            gitRefUpdated,
+            allUsers,
+            NAME_GROUPS,
+            () -> ReviewDb.FIRST_GROUP_ID,
+            groupBatchSize);
 
     nextIdLatency =
         metrics.newTimer(
@@ -158,9 +162,4 @@
   private static int nextChangeId(ReviewDb db) throws OrmException {
     return db.nextChangeId();
   }
-
-  @SuppressWarnings("deprecation")
-  static int nextGroupId(ReviewDb db) throws OrmException {
-    return db.nextAccountGroupId();
-  }
 }
diff --git a/java/com/google/gerrit/server/config/GerritGlobalModule.java b/java/com/google/gerrit/server/config/GerritGlobalModule.java
index b4f9cc7..b26e875 100644
--- a/java/com/google/gerrit/server/config/GerritGlobalModule.java
+++ b/java/com/google/gerrit/server/config/GerritGlobalModule.java
@@ -170,6 +170,7 @@
 import com.google.gerrit.server.query.change.ChangeQueryBuilder;
 import com.google.gerrit.server.query.change.ChangeQueryProcessor;
 import com.google.gerrit.server.query.change.ConflictsCacheImpl;
+import com.google.gerrit.server.quota.QuotaEnforcer;
 import com.google.gerrit.server.restapi.change.SuggestReviewers;
 import com.google.gerrit.server.restapi.group.GroupModule;
 import com.google.gerrit.server.rules.DefaultSubmitRule;
@@ -394,6 +395,7 @@
     DynamicItem.itemOf(binder(), MergeSuperSetComputation.class);
     DynamicItem.itemOf(binder(), ProjectNameLockManager.class);
     DynamicSet.setOf(binder(), SubmitRule.class);
+    DynamicSet.setOf(binder(), QuotaEnforcer.class);
 
     DynamicMap.mapOf(binder(), MailFilter.class);
     bind(MailFilter.class).annotatedWith(Exports.named("ListMailFilter")).to(ListMailFilter.class);
diff --git a/java/com/google/gerrit/server/git/DefaultAdvertiseRefsHook.java b/java/com/google/gerrit/server/git/DefaultAdvertiseRefsHook.java
index be8fcdb..f255ea2 100644
--- a/java/com/google/gerrit/server/git/DefaultAdvertiseRefsHook.java
+++ b/java/com/google/gerrit/server/git/DefaultAdvertiseRefsHook.java
@@ -14,10 +14,10 @@
 
 package com.google.gerrit.server.git;
 
-import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import java.io.IOException;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import org.eclipse.jgit.lib.Ref;
@@ -49,13 +49,12 @@
       if (prefixes.isEmpty() || prefixes.get(0).isEmpty()) {
         refs = repo.getAllRefs();
       } else {
-        ImmutableMap.Builder<String, Ref> b = new ImmutableMap.Builder<>();
+        refs = new HashMap<>();
         for (String prefix : prefixes) {
           for (Ref ref : repo.getRefDatabase().getRefsByPrefix(prefix)) {
-            b.put(ref.getName(), ref);
+            refs.put(ref.getName(), ref);
           }
         }
-        refs = b.build();
       }
       return perm.filter(refs, repo, opts);
     } catch (IOException | PermissionBackendException e) {
diff --git a/java/com/google/gerrit/server/git/meta/MetaDataUpdate.java b/java/com/google/gerrit/server/git/meta/MetaDataUpdate.java
index bbe0c62..97beefd 100644
--- a/java/com/google/gerrit/server/git/meta/MetaDataUpdate.java
+++ b/java/com/google/gerrit/server/git/meta/MetaDataUpdate.java
@@ -22,6 +22,7 @@
 import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
+import com.google.inject.Singleton;
 import com.google.inject.assistedinject.Assisted;
 import java.io.IOException;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
@@ -33,21 +34,22 @@
 
 /** Helps with the updating of a {@link VersionedMetaData}. */
 public class MetaDataUpdate implements AutoCloseable {
+  @Singleton
   public static class User {
     private final InternalFactory factory;
     private final GitRepositoryManager mgr;
-    private final PersonIdent serverIdent;
+    private final Provider<PersonIdent> serverIdentProvider;
     private final Provider<IdentifiedUser> identifiedUser;
 
     @Inject
     User(
         InternalFactory factory,
         GitRepositoryManager mgr,
-        @GerritPersonIdent PersonIdent serverIdent,
+        @GerritPersonIdent Provider<PersonIdent> serverIdentProvider,
         Provider<IdentifiedUser> identifiedUser) {
       this.factory = factory;
       this.mgr = mgr;
-      this.serverIdent = serverIdent;
+      this.serverIdentProvider = serverIdentProvider;
       this.identifiedUser = identifiedUser;
     }
 
@@ -126,29 +128,31 @@
     public MetaDataUpdate create(
         Project.NameKey name, Repository repository, IdentifiedUser user, BatchRefUpdate batch) {
       MetaDataUpdate md = factory.create(name, repository, batch);
-      md.getCommitBuilder().setCommitter(serverIdent);
+      md.getCommitBuilder().setCommitter(serverIdentProvider.get());
       md.setAuthor(user);
       return md;
     }
 
     private PersonIdent createPersonIdent(IdentifiedUser user) {
+      PersonIdent serverIdent = serverIdentProvider.get();
       return user.newCommitterIdent(serverIdent.getWhen(), serverIdent.getTimeZone());
     }
   }
 
+  @Singleton
   public static class Server {
     private final InternalFactory factory;
     private final GitRepositoryManager mgr;
-    private final PersonIdent serverIdent;
+    private final Provider<PersonIdent> serverIdentProvider;
 
     @Inject
     Server(
         InternalFactory factory,
         GitRepositoryManager mgr,
-        @GerritPersonIdent PersonIdent serverIdent) {
+        @GerritPersonIdent Provider<PersonIdent> serverIdentProvider) {
       this.factory = factory;
       this.mgr = mgr;
-      this.serverIdent = serverIdent;
+      this.serverIdentProvider = serverIdentProvider;
     }
 
     public MetaDataUpdate create(Project.NameKey name)
@@ -162,6 +166,7 @@
       Repository repo = mgr.openRepository(name);
       MetaDataUpdate md = factory.create(name, repo, batch);
       md.setCloseRepository(true);
+      PersonIdent serverIdent = serverIdentProvider.get();
       md.getCommitBuilder().setAuthor(serverIdent);
       md.getCommitBuilder().setCommitter(serverIdent);
       return md;
diff --git a/java/com/google/gerrit/server/git/receive/ReceiveCommits.java b/java/com/google/gerrit/server/git/receive/ReceiveCommits.java
index b23fe71..cdfd00d 100644
--- a/java/com/google/gerrit/server/git/receive/ReceiveCommits.java
+++ b/java/com/google/gerrit/server/git/receive/ReceiveCommits.java
@@ -1753,9 +1753,10 @@
           reject(cmd, "cannot use merged with base");
           return;
         }
-        RevCommit branchTip = readBranchTip(cmd, magicBranch.dest);
+        RevCommit branchTip = readBranchTip(magicBranch.dest);
         if (branchTip == null) {
-          return; // readBranchTip already rejected cmd.
+          reject(cmd, magicBranch.dest.get() + " not found");
+          return;
         }
         if (!walk.isMergedInto(tip, branchTip)) {
           reject(cmd, "not merged into branch");
@@ -1793,12 +1794,21 @@
           }
         }
       } else if (newChangeForAllNotInTarget) {
-        RevCommit branchTip = readBranchTip(cmd, magicBranch.dest);
-        if (branchTip == null) {
-          return; // readBranchTip already rejected cmd.
+        RevCommit branchTip = readBranchTip(magicBranch.dest);
+        if (branchTip != null) {
+          magicBranch.baseCommit = Collections.singletonList(branchTip);
+          logger.atFine().log("Set baseCommit = %s", magicBranch.baseCommit.get(0).name());
+        } else {
+          // The target branch does not exist. Usually pushing changes for review requires that the
+          // target branch exists, but there is an exception for the branch to which HEAD points to
+          // and for refs/meta/config. Pushing for review to these branches is allowed even if the
+          // branch does not exist yet. This allows to push initial code for review to an empty
+          // repository and to review an initial project configuration.
+          if (!ref.equals(readHEAD(repo)) && !ref.equals(RefNames.REFS_CONFIG)) {
+            reject(cmd, magicBranch.dest.get() + " not found");
+            return;
+          }
         }
-        magicBranch.baseCommit = Collections.singletonList(branchTip);
-        logger.atFine().log("Set baseCommit = %s", magicBranch.baseCommit.get(0).name());
       }
     } catch (IOException ex) {
       logger.atWarning().withCause(ex).log(
@@ -1872,10 +1882,9 @@
     }
   }
 
-  private RevCommit readBranchTip(ReceiveCommand cmd, Branch.NameKey branch) throws IOException {
+  private RevCommit readBranchTip(Branch.NameKey branch) throws IOException {
     Ref r = allRefs().get(branch.get());
     if (r == null) {
-      reject(cmd, branch.get() + " not found");
       return null;
     }
     return receivePack.getRevWalk().parseCommit(r.getObjectId());
@@ -2727,10 +2736,13 @@
 
     /** prints a warning if the new PS has the same tree as the previous commit. */
     private void sameTreeWarning() throws IOException {
-      RevCommit newCommit = receivePack.getRevWalk().parseCommit(newCommitId);
+      RevWalk rw = receivePack.getRevWalk();
+      RevCommit newCommit = rw.parseCommit(newCommitId);
       RevCommit priorCommit = revisions.inverse().get(priorPatchSet);
 
       if (newCommit.getTree().equals(priorCommit.getTree())) {
+        rw.parseBody(newCommit);
+        rw.parseBody(priorCommit);
         boolean messageEq =
             Objects.equals(newCommit.getFullMessage(), priorCommit.getFullMessage());
         boolean parentsEq = parentsEqual(newCommit, priorCommit);
diff --git a/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java b/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java
new file mode 100644
index 0000000..8aa86b1
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java
@@ -0,0 +1,149 @@
+// Copyright (C) 2018 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.server.quota;
+
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Project.NameKey;
+import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.plugincontext.PluginSetContext;
+import com.google.gerrit.server.plugincontext.PluginSetEntryContext;
+import java.util.ArrayList;
+import java.util.List;
+import javax.inject.Inject;
+import javax.inject.Provider;
+import javax.inject.Singleton;
+
+@Singleton
+public class DefaultQuotaBackend implements QuotaBackend {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  private final Provider<CurrentUser> userProvider;
+  private final PluginSetContext<QuotaEnforcer> quotaEnforcers;
+
+  @Inject
+  DefaultQuotaBackend(
+      Provider<CurrentUser> userProvider, PluginSetContext<QuotaEnforcer> quotaEnforcers) {
+    this.userProvider = userProvider;
+    this.quotaEnforcers = quotaEnforcers;
+  }
+
+  @Override
+  public WithUser currentUser() {
+    return new WithUser(quotaEnforcers, userProvider.get());
+  }
+
+  @Override
+  public WithUser user(CurrentUser user) {
+    return new WithUser(quotaEnforcers, user);
+  }
+
+  private static QuotaResponse.Aggregated request(
+      PluginSetContext<QuotaEnforcer> quotaEnforcers,
+      String quotaGroup,
+      QuotaRequestContext requestContext,
+      long numTokens,
+      boolean deduct) {
+    checkState(numTokens > 0, "numTokens must be a positive, non-zero long");
+
+    // PluginSets can change their content when plugins (de-)register. Copy the currently registered
+    // plugins so that we can iterate twice on a stable list.
+    List<PluginSetEntryContext<QuotaEnforcer>> enforcers = ImmutableList.copyOf(quotaEnforcers);
+    List<QuotaResponse> responses = new ArrayList<>(enforcers.size());
+    for (PluginSetEntryContext<QuotaEnforcer> enforcer : enforcers) {
+      try {
+        if (deduct) {
+          responses.add(enforcer.call(p -> p.requestTokens(quotaGroup, requestContext, numTokens)));
+        } else {
+          responses.add(enforcer.call(p -> p.dryRun(quotaGroup, requestContext, numTokens)));
+        }
+      } catch (RuntimeException e) {
+        logger.atSevere().withCause(e).log("exception while enforcing quota");
+        responses.add(QuotaResponse.error(e.getMessage()));
+      }
+    }
+
+    if (deduct && responses.stream().anyMatch(r -> r.status().isError())) {
+      // Roll back the quota request for all enforcers that deducted the quota (= the request
+      // succeeded). Don't touch failed enforcers as the interface contract said that failed
+      // requests should not be deducted.
+      for (int i = 0; i < responses.size(); i++) {
+        if (responses.get(i).status().isOk()) {
+          enforcers.get(i).run(p -> p.refill(quotaGroup, requestContext, numTokens));
+        }
+      }
+    }
+
+    logger.atFine().log(
+        "Quota request for %s with %s (deduction=%s) for %s token returned %s",
+        quotaGroup,
+        requestContext,
+        deduct ? "(deduction=yes)" : "(deduction=no)",
+        numTokens,
+        responses);
+    return new AutoValue_QuotaResponse_Aggregated(ImmutableList.copyOf(responses));
+  }
+
+  static class WithUser extends WithResource implements QuotaBackend.WithUser {
+    WithUser(PluginSetContext<QuotaEnforcer> quotaEnforcers, CurrentUser user) {
+      super(quotaEnforcers, QuotaRequestContext.builder().user(user).build());
+    }
+
+    @Override
+    public QuotaBackend.WithResource account(Account.Id account) {
+      QuotaRequestContext ctx = requestContext.toBuilder().account(account).build();
+      return new WithResource(quotaEnforcers, ctx);
+    }
+
+    @Override
+    public QuotaBackend.WithResource project(NameKey project) {
+      QuotaRequestContext ctx = requestContext.toBuilder().project(project).build();
+      return new WithResource(quotaEnforcers, ctx);
+    }
+
+    @Override
+    public QuotaBackend.WithResource change(Change.Id change, NameKey project) {
+      QuotaRequestContext ctx = requestContext.toBuilder().change(change).project(project).build();
+      return new WithResource(quotaEnforcers, ctx);
+    }
+  }
+
+  static class WithResource implements QuotaBackend.WithResource {
+    protected final QuotaRequestContext requestContext;
+    protected final PluginSetContext<QuotaEnforcer> quotaEnforcers;
+
+    private WithResource(
+        PluginSetContext<QuotaEnforcer> quotaEnforcers, QuotaRequestContext quotaRequestContext) {
+      this.quotaEnforcers = quotaEnforcers;
+      this.requestContext = quotaRequestContext;
+    }
+
+    @Override
+    public QuotaResponse.Aggregated requestTokens(String quotaGroup, long numTokens) {
+      return DefaultQuotaBackend.request(
+          quotaEnforcers, quotaGroup, requestContext, numTokens, true);
+    }
+
+    @Override
+    public QuotaResponse.Aggregated dryRun(String quotaGroup, long numTokens) {
+      return DefaultQuotaBackend.request(
+          quotaEnforcers, quotaGroup, requestContext, numTokens, false);
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/quota/QuotaBackend.java b/java/com/google/gerrit/server/quota/QuotaBackend.java
new file mode 100644
index 0000000..d4dc46d
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/QuotaBackend.java
@@ -0,0 +1,86 @@
+// Copyright (C) 2018 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.server.quota;
+
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.server.CurrentUser;
+import com.google.inject.ImplementedBy;
+
+/**
+ * Backend interface to perform quota requests on. By default, this interface is backed by {@link
+ * DefaultQuotaBackend} which calls all plugins that implement {@link QuotaEnforcer}. A different
+ * implementation might be bound in tests. Plugins are not supposed to implement this interface, but
+ * bind a {@link QuotaEnforcer} implementation instead.
+ *
+ * <p>All quota requests require a quota group and a user. Enriching them with a top-level entity
+ * {@code Change, Project, Account} is optional but should be done if the request is targeted.
+ *
+ * <p>Example usage:
+ *
+ * <pre>
+ *   quotaBackend.currentUser().project(projectName).requestToken("/projects/create").throwOnError();
+ *   quotaBackend.user(user).requestToken("/restapi/config/put").throwOnError();
+ *   QuotaResponse.Aggregated result = quotaBackend.currentUser().account(accountId).requestToken("/restapi/accounts/emails/validate");
+ *   QuotaResponse.Aggregated result = quotaBackend.currentUser().project(projectName).requestTokens("/projects/git/upload", numBytesInPush);
+ * </pre>
+ *
+ * <p>All quota groups must be documented in {@code quota.txt} and detail the metadata that is
+ * provided (i.e. the parameters used to scope down the quota request).
+ */
+@ImplementedBy(DefaultQuotaBackend.class)
+public interface QuotaBackend {
+  /** Constructs a request for the current user. */
+  WithUser currentUser();
+
+  /**
+   * See {@link #currentUser()}. Use this method only if you can't guarantee that the request is for
+   * the current user (e.g. impersonation).
+   */
+  WithUser user(CurrentUser user);
+
+  /**
+   * An interface capable of issuing quota requests. Scope can be futher reduced by providing a
+   * top-level entity.
+   */
+  interface WithUser extends WithResource {
+    /** Scope the request down to an account. */
+    WithResource account(Account.Id account);
+
+    /** Scope the request down to a project. */
+    WithResource project(Project.NameKey project);
+
+    /** Scope the request down to a change. */
+    WithResource change(Change.Id change, Project.NameKey project);
+  }
+
+  /** An interface capable of issuing quota requests. */
+  interface WithResource {
+    /** Issues a single quota request for {@code 1} token. */
+    default QuotaResponse.Aggregated requestToken(String quotaGroup) {
+      return requestTokens(quotaGroup, 1);
+    }
+
+    /** Issues a single quota request for {@code numTokens} tokens. */
+    QuotaResponse.Aggregated requestTokens(String quotaGroup, long numTokens);
+
+    /**
+     * Issues a single quota request for {@code numTokens} tokens but signals the implementations
+     * not to deduct any quota yet. Can be used to do pre-flight requests where necessary
+     */
+    QuotaResponse.Aggregated dryRun(String quotaGroup, long tokens);
+  }
+}
diff --git a/java/com/google/gerrit/server/quota/QuotaEnforcer.java b/java/com/google/gerrit/server/quota/QuotaEnforcer.java
new file mode 100644
index 0000000..9c55e11
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/QuotaEnforcer.java
@@ -0,0 +1,72 @@
+// Copyright (C) 2018 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.server.quota;
+
+import com.google.gerrit.extensions.annotations.ExtensionPoint;
+
+/**
+ * Allows plugins to enforce different types of quota.
+ *
+ * <p>Enforcing quotas can be helpful in many scenarios. For example:
+ *
+ * <ul>
+ *   <li>Reducing the number of QPS a user can send to Gerrit on the REST API
+ *   <li>Limiting the size of a repository (project)
+ *   <li>Limiting the number of changes in a repository
+ *   <li>Limiting the number of actions that have the potential for spam, abuse or flooding if not
+ *       limited
+ * </ul>
+ *
+ * This endpoint gives plugins the capability to enforce any of these limits. The server will ask
+ * all plugins that registered this endpoint and collect all results. In case {@link
+ * #requestTokens(String, QuotaRequestContext, long)} was called and one or more plugins returned an
+ * erroneous result, the server will call {@link #refill(String, QuotaRequestContext, long)} on all
+ * plugins with the same parameters. Plugins that deducted tokens in the {@link
+ * #requestTokens(String, QuotaRequestContext, long)} call can refill them so that users don't get
+ * charged any quota for failed requests.
+ *
+ * <p>Not all implementations will need to deduct quota on {@link #requestTokens(String,
+ * QuotaRequestContext, long)}}. Implementations that work on top of instance-attributes, such as
+ * the number of projects per instance can choose not to keep any state and always check how many
+ * existing projects there are and if adding the inquired number would exceed the limit. In this
+ * case, {@link #requestTokens(String, QuotaRequestContext, long)} and {@link #dryRun(String,
+ * QuotaRequestContext, long)} share the same implementation and {@link #refill(String,
+ * QuotaRequestContext, long)} is a no-op.
+ */
+@ExtensionPoint
+public interface QuotaEnforcer {
+  /**
+   * Checks if there is at least {@code numTokens} quota to fulfil the request. Bucket-based
+   * implementations can deduct the inquired number of tokens from the bucket.
+   */
+  QuotaResponse requestTokens(String quotaGroup, QuotaRequestContext ctx, long numTokens);
+
+  /**
+   * Checks if there is at least {@code numTokens} quota to fulfil the request. This is a pre-flight
+   * request, implementations should not deduct tokens from a bucket, yet.
+   */
+  QuotaResponse dryRun(String quotaGroup, QuotaRequestContext ctx, long numTokens);
+
+  /**
+   * A previously requested and deducted quota has to be refilled (if possible) because the request
+   * failed other quota checks. Implementations can choose to leave this a no-op in case they are
+   * the first line of defence (e.g. always deduct HTTP quota even if the request failed for other
+   * quota issues so that the user gets throttled).
+   *
+   * <p>Will not be called if the {@link #requestTokens(String, QuotaRequestContext, long)} call
+   * returned {@link QuotaResponse.Status#NO_OP}.
+   */
+  void refill(String quotaGroup, QuotaRequestContext ctx, long numTokens);
+}
diff --git a/java/com/google/gerrit/server/quota/QuotaException.java b/java/com/google/gerrit/server/quota/QuotaException.java
new file mode 100644
index 0000000..56877b2
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/QuotaException.java
@@ -0,0 +1,27 @@
+// Copyright (C) 2018 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.server.quota;
+
+import com.google.gerrit.extensions.restapi.RestApiException;
+
+/**
+ * Exception that was encountered while checking if there is sufficient quota to fulfil the request.
+ * Can be propagated directly to the REST API.
+ */
+public class QuotaException extends RestApiException {
+  public QuotaException(String reason) {
+    super(reason);
+  }
+}
diff --git a/java/com/google/gerrit/server/quota/QuotaRequestContext.java b/java/com/google/gerrit/server/quota/QuotaRequestContext.java
new file mode 100644
index 0000000..90b501c
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/QuotaRequestContext.java
@@ -0,0 +1,54 @@
+// Copyright (C) 2018 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.server.quota;
+
+import com.google.auto.value.AutoValue;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.server.AnonymousUser;
+import com.google.gerrit.server.CurrentUser;
+import java.util.Optional;
+
+@AutoValue
+public abstract class QuotaRequestContext {
+
+  public static Builder builder() {
+    return new AutoValue_QuotaRequestContext.Builder().user(new AnonymousUser());
+  }
+
+  public abstract CurrentUser user();
+
+  public abstract Optional<Project.NameKey> project();
+
+  public abstract Optional<Change.Id> change();
+
+  public abstract Optional<Account.Id> account();
+
+  public abstract Builder toBuilder();
+
+  @AutoValue.Builder
+  public abstract static class Builder {
+    public abstract QuotaRequestContext.Builder user(CurrentUser user);
+
+    public abstract QuotaRequestContext.Builder account(Account.Id account);
+
+    public abstract QuotaRequestContext.Builder project(Project.NameKey project);
+
+    public abstract QuotaRequestContext.Builder change(Change.Id change);
+
+    public abstract QuotaRequestContext build();
+  }
+}
diff --git a/java/com/google/gerrit/server/quota/QuotaResponse.java b/java/com/google/gerrit/server/quota/QuotaResponse.java
new file mode 100644
index 0000000..c239aaf
--- /dev/null
+++ b/java/com/google/gerrit/server/quota/QuotaResponse.java
@@ -0,0 +1,113 @@
+// Copyright (C) 2018 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.server.quota;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+@AutoValue
+public abstract class QuotaResponse {
+  public enum Status {
+    /** The quota requests succeeded. */
+    OK,
+
+    /**
+     * The quota succeeded, but was a no-op because the plugin does not enforce this quota group
+     * (equivalent to OK, but relevant for debugging).
+     */
+    NO_OP,
+
+    /**
+     * The requested quota could not be allocated. This status code is not used to indicate
+     * processing failures as these are propagated as {@code RuntimeException}s.
+     */
+    ERROR;
+
+    public boolean isOk() {
+      return this == OK;
+    }
+
+    public boolean isError() {
+      return this == ERROR;
+    }
+  }
+
+  public static QuotaResponse ok() {
+    return new AutoValue_QuotaResponse.Builder().status(Status.OK).build();
+  }
+
+  public static QuotaResponse noOp() {
+    return new AutoValue_QuotaResponse.Builder().status(Status.NO_OP).build();
+  }
+
+  public static QuotaResponse error(String message) {
+    return new AutoValue_QuotaResponse.Builder().status(Status.ERROR).message(message).build();
+  }
+
+  public abstract Status status();
+
+  public abstract Optional<String> message();
+
+  @AutoValue.Builder
+  public abstract static class Builder {
+    public abstract QuotaResponse.Builder status(Status status);
+
+    public abstract QuotaResponse.Builder message(String message);
+
+    public abstract QuotaResponse build();
+  }
+
+  @AutoValue
+  public abstract static class Aggregated {
+    protected abstract ImmutableList<QuotaResponse> responses();
+
+    public boolean hasError() {
+      return responses().stream().anyMatch(r -> r.status().isError());
+    }
+
+    public ImmutableList<QuotaResponse> all() {
+      return responses();
+    }
+
+    public ImmutableList<QuotaResponse> ok() {
+      return responses().stream().filter(r -> r.status().isOk()).collect(toImmutableList());
+    }
+
+    public ImmutableList<QuotaResponse> error() {
+      return responses().stream().filter(r -> r.status().isError()).collect(toImmutableList());
+    }
+
+    public String errorMessage() {
+      return error()
+          .stream()
+          .map(QuotaResponse::message)
+          .flatMap(Streams::stream)
+          .collect(Collectors.joining(", "));
+    }
+
+    public void throwOnError() throws QuotaException {
+      String errorMessage = errorMessage();
+      if (!Strings.isNullOrEmpty(errorMessage)) {
+        throw new QuotaException(errorMessage);
+      }
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/schema/Schema_155.java b/java/com/google/gerrit/server/schema/Schema_155.java
index 812d7a6..e9372a5 100644
--- a/java/com/google/gerrit/server/schema/Schema_155.java
+++ b/java/com/google/gerrit/server/schema/Schema_155.java
@@ -40,15 +40,13 @@
 
   @Override
   protected void migrateData(ReviewDb db, UpdateUI ui) throws OrmException, SQLException {
-    @SuppressWarnings("deprecation")
-    RepoSequence.Seed accountSeed = db::nextAccountId;
     RepoSequence accountSeq =
         new RepoSequence(
             repoManager,
             GitReferenceUpdated.DISABLED,
             allUsersName,
             Sequences.NAME_ACCOUNTS,
-            accountSeed,
+            () -> ReviewDb.FIRST_ACCOUNT_ID,
             1);
 
     // consume one account ID to ensure that the account sequence is initialized in NoteDb
diff --git a/java/com/google/gerrit/server/schema/Schema_163.java b/java/com/google/gerrit/server/schema/Schema_163.java
index 9eb5d5e..4b3659de 100644
--- a/java/com/google/gerrit/server/schema/Schema_163.java
+++ b/java/com/google/gerrit/server/schema/Schema_163.java
@@ -40,15 +40,13 @@
 
   @Override
   protected void migrateData(ReviewDb db, UpdateUI ui) throws OrmException, SQLException {
-    @SuppressWarnings("deprecation")
-    RepoSequence.Seed groupSeed = db::nextAccountGroupId;
     RepoSequence groupSeq =
         new RepoSequence(
             repoManager,
             GitReferenceUpdated.DISABLED,
             allUsersName,
             Sequences.NAME_GROUPS,
-            groupSeed,
+            () -> ReviewDb.FIRST_GROUP_ID,
             1);
 
     // consume one account ID to ensure that the group sequence is initialized in NoteDb
diff --git a/java/com/google/gerrit/testing/DisabledReviewDb.java b/java/com/google/gerrit/testing/DisabledReviewDb.java
index 2bf95b0..d06beb9 100644
--- a/java/com/google/gerrit/testing/DisabledReviewDb.java
+++ b/java/com/google/gerrit/testing/DisabledReviewDb.java
@@ -95,16 +95,6 @@
   }
 
   @Override
-  public int nextAccountId() {
-    throw new Disabled();
-  }
-
-  @Override
-  public int nextAccountGroupId() {
-    throw new Disabled();
-  }
-
-  @Override
   public int nextChangeId() {
     throw new Disabled();
   }
diff --git a/java/com/google/gerrit/testing/FakeGroupAuditService.java b/java/com/google/gerrit/testing/FakeGroupAuditService.java
index f2e85cd..ddf03f5 100644
--- a/java/com/google/gerrit/testing/FakeGroupAuditService.java
+++ b/java/com/google/gerrit/testing/FakeGroupAuditService.java
@@ -63,7 +63,10 @@
 
   @Override
   public void dispatch(AuditEvent action) {
-    auditEvents.add(action);
+    synchronized (auditEvents) {
+      auditEvents.add(action);
+      auditEvents.notifyAll();
+    }
   }
 
   @Override
diff --git a/java/com/google/gerrit/util/http/RequestUtil.java b/java/com/google/gerrit/util/http/RequestUtil.java
index 2a359ca..2543ada 100644
--- a/java/com/google/gerrit/util/http/RequestUtil.java
+++ b/java/com/google/gerrit/util/http/RequestUtil.java
@@ -56,5 +56,38 @@
     return pathInfo;
   }
 
+  /**
+   * Trims leading '/' and 'a/'. Removes the context path, but keeps the servlet path. Removes all
+   * IDs from the rest of the URI.
+   *
+   * <p>The returned string is a good fit for cases where one wants the full context of the request
+   * without any identifiable data. For example: Logging or quota checks.
+   *
+   * <p>Examples:
+   *
+   * <ul>
+   *   <li>/a/accounts/self/detail => /accounts/detail
+   *   <li>/changes/123/revisions/current/detail => /changes/revisions/detail
+   *   <li>/changes/ => /changes
+   * </ul>
+   */
+  public static String getRestPathWithoutIds(HttpServletRequest req) {
+    String encodedPathInfo = req.getRequestURI().substring(req.getContextPath().length());
+    if (encodedPathInfo.startsWith("/")) {
+      encodedPathInfo = encodedPathInfo.substring(1);
+    }
+    if (encodedPathInfo.startsWith("a/")) {
+      encodedPathInfo = encodedPathInfo.substring(2);
+    }
+
+    String[] parts = encodedPathInfo.split("/");
+    StringBuilder result = new StringBuilder(parts.length);
+    for (int i = 0; i < parts.length; i = i + 2) {
+      result.append("/");
+      result.append(parts[i]);
+    }
+    return result.toString();
+  }
+
   private RequestUtil() {}
 }
diff --git a/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java b/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
index 6f25d28..18eb37a 100644
--- a/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/group/GroupsIT.java
@@ -89,14 +89,13 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 import java.sql.Timestamp;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.Stream;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
 import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.CommitBuilder;
@@ -334,9 +333,6 @@
     String p = createUniqueGroup();
     String g1 = createUniqueGroup();
     String g2 = createUniqueGroup();
-    List<String> groups = new ArrayList<>();
-    groups.add(g1);
-    groups.add(g2);
     gApi.groups().id(p).addGroups(g1, g2);
     assertIncludes(p, g1, g2);
   }
@@ -952,8 +948,8 @@
   }
 
   /**
-   * @Sandboxed is used by this test because it deletes a group reference which introduces an
-   * inconsistency for the group storage. Once group deletion is supported, this test should be
+   * {@code @Sandboxed} is used by this test because it deletes a group reference which introduces
+   * an inconsistency for the group storage. Once group deletion is supported, this test should be
    * updated to use the API instead.
    */
   @Test
@@ -1001,8 +997,7 @@
     TestAccount groupOwner = accountCreator.user2();
     GroupInput in = new GroupInput();
     in.name = name("group");
-    in.members =
-        Collections.singleton(groupOwner).stream().map(u -> u.id.toString()).collect(toList());
+    in.members = Stream.of(groupOwner).map(u -> u.id.toString()).collect(toList());
     in.visibleToAll = true;
     GroupInfo group = gApi.groups().create(in).get();
 
@@ -1045,7 +1040,7 @@
 
   @Test
   public void pushToGroupsBranchForNonAllUsersRepo() throws Exception {
-    assertCreateGroupBranch(project, null);
+    assertCreateGroupBranch(project);
     String groupRef =
         RefNames.refsGroups(new AccountGroup.UUID(gApi.groups().create(name("foo")).get().id));
     createBranch(project, groupRef);
@@ -1054,7 +1049,7 @@
 
   @Test
   public void pushToDeletedGroupsBranchForNonAllUsersRepo() throws Exception {
-    assertCreateGroupBranch(project, null);
+    assertCreateGroupBranch(project);
     String groupRef =
         RefNames.refsDeletedGroups(
             new AccountGroup.UUID(gApi.groups().create(name("foo")).get().id));
@@ -1092,8 +1087,7 @@
     }
   }
 
-  private void assertCreateGroupBranch(Project.NameKey project, String expectedErrorOnCreate)
-      throws Exception {
+  private void assertCreateGroupBranch(Project.NameKey project) throws Exception {
     grant(project, RefNames.REFS_GROUPS + "*", Permission.CREATE, false, REGISTERED_USERS);
     grant(project, RefNames.REFS_GROUPS + "*", Permission.PUSH, false, REGISTERED_USERS);
     TestRepository<InMemoryRepository> repo = cloneProject(project);
@@ -1102,11 +1096,7 @@
             .create(db, admin.getIdent(), repo, "Update group", "arbitraryFile.txt", "some content")
             .setParents(ImmutableList.of())
             .to(RefNames.REFS_GROUPS + name("bar"));
-    if (expectedErrorOnCreate != null) {
-      r.assertErrorStatus(expectedErrorOnCreate);
-    } else {
-      r.assertOkStatus();
-    }
+    r.assertOkStatus();
   }
 
   @Test
@@ -1495,7 +1485,7 @@
   private void assertMembers(String group, TestAccount... expectedMembers) throws Exception {
     assertMembers(
         gApi.groups().id(group).members(),
-        TestAccount.names(expectedMembers).stream().toArray(String[]::new));
+        TestAccount.names(expectedMembers).toArray(new String[0]));
     assertAccountInfos(Arrays.asList(expectedMembers), gApi.groups().id(group).members());
   }
 
diff --git a/javatests/com/google/gerrit/acceptance/git/AbstractPushForReview.java b/javatests/com/google/gerrit/acceptance/git/AbstractPushForReview.java
index 228784b..7529ee3 100644
--- a/javatests/com/google/gerrit/acceptance/git/AbstractPushForReview.java
+++ b/javatests/com/google/gerrit/acceptance/git/AbstractPushForReview.java
@@ -221,6 +221,18 @@
   @Test
   @TestProjectInput(createEmptyCommit = false)
   public void pushInitialCommitSeriesForMasterBranch() throws Exception {
+    testPushInitialCommitSeriesForMasterBranch();
+  }
+
+  @Test
+  @TestProjectInput(createEmptyCommit = false)
+  public void pushInitialCommitSeriesForMasterBranchWithCreateNewChangeForAllNotInTarget()
+      throws Exception {
+    enableCreateNewChangeForAllNotInTarget();
+    testPushInitialCommitSeriesForMasterBranch();
+  }
+
+  private void testPushInitialCommitSeriesForMasterBranch() throws Exception {
     RevCommit c = testRepo.commit().message("Initial commit").insertChangeId().create();
     String id = GitUtil.getChangeId(testRepo, c).get();
     testRepo.reset(c);
@@ -1464,14 +1476,7 @@
 
   @Test
   public void pushSameCommitTwice() throws Exception {
-    try (ProjectConfigUpdate u = updateProject(project)) {
-      u.getConfig()
-          .getProject()
-          .setBooleanConfig(
-              BooleanProjectConfig.CREATE_NEW_CHANGE_FOR_ALL_NOT_IN_TARGET,
-              InheritableBoolean.TRUE);
-      u.save();
-    }
+    enableCreateNewChangeForAllNotInTarget();
 
     PushOneCommit push =
         pushFactory.create(
@@ -1493,14 +1498,7 @@
 
   @Test
   public void pushSameCommitTwiceWhenIndexFailed() throws Exception {
-    try (ProjectConfigUpdate u = updateProject(project)) {
-      u.getConfig()
-          .getProject()
-          .setBooleanConfig(
-              BooleanProjectConfig.CREATE_NEW_CHANGE_FOR_ALL_NOT_IN_TARGET,
-              InheritableBoolean.TRUE);
-      u.save();
-    }
+    enableCreateNewChangeForAllNotInTarget();
 
     PushOneCommit push =
         pushFactory.create(
@@ -2356,6 +2354,113 @@
     assertPushOk(pr, "refs/heads/permitted");
   }
 
+  @Test
+  public void pushCommitsWithSameTreeNoChanges() throws Exception {
+    RevCommit c =
+        testRepo
+            .commit()
+            .message("Foo")
+            .parent(getHead(testRepo.getRepository()))
+            .insertChangeId()
+            .create();
+    testRepo.reset(c);
+
+    String r = "refs/for/master";
+    PushResult pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+
+    RevCommit amended = testRepo.amend(c).create();
+    testRepo.reset(amended);
+
+    pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+    assertThat(pr.getMessages())
+        .contains(
+            "warning: no changes between prior commit "
+                + c.abbreviate(7).name()
+                + " and new commit "
+                + amended.abbreviate(7).name());
+  }
+
+  @Test
+  public void pushCommitsWithSameTreeNoFilesChangedMessageUpdated() throws Exception {
+    RevCommit c =
+        testRepo
+            .commit()
+            .message("Foo")
+            .parent(getHead(testRepo.getRepository()))
+            .insertChangeId()
+            .create();
+    String id = GitUtil.getChangeId(testRepo, c).get();
+    testRepo.reset(c);
+
+    String r = "refs/for/master";
+    PushResult pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+
+    RevCommit amended =
+        testRepo.amend(c).message("Foo Bar").insertChangeId(id.substring(1)).create();
+    testRepo.reset(amended);
+
+    pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+    assertThat(pr.getMessages())
+        .contains(
+            "warning: " + amended.abbreviate(7).name() + ": no files changed, message updated");
+  }
+
+  @Test
+  public void pushCommitsWithSameTreeNoFilesChangedAuthorChanged() throws Exception {
+    RevCommit c =
+        testRepo
+            .commit()
+            .message("Foo")
+            .parent(getHead(testRepo.getRepository()))
+            .insertChangeId()
+            .create();
+    testRepo.reset(c);
+
+    String r = "refs/for/master";
+    PushResult pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+
+    RevCommit amended = testRepo.amend(c).author(user.getIdent()).create();
+    testRepo.reset(amended);
+
+    pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+    assertThat(pr.getMessages())
+        .contains(
+            "warning: " + amended.abbreviate(7).name() + ": no files changed, author changed");
+  }
+
+  @Test
+  public void pushCommitsWithSameTreeNoFilesChangedWasRebased() throws Exception {
+    RevCommit head = getHead(testRepo.getRepository());
+    RevCommit c = testRepo.commit().message("Foo").parent(head).insertChangeId().create();
+    testRepo.reset(c);
+
+    String r = "refs/for/master";
+    PushResult pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+
+    testRepo.reset(head);
+    RevCommit newBase = testRepo.commit().message("Base").parent(head).insertChangeId().create();
+    testRepo.reset(newBase);
+
+    pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+
+    testRepo.reset(c);
+    RevCommit amended = testRepo.amend(c).parent(newBase).create();
+    testRepo.reset(amended);
+
+    pr = pushHead(testRepo, r, false);
+    assertPushOk(pr, r);
+    assertThat(pr.getMessages())
+        .contains("warning: " + amended.abbreviate(7).name() + ": no files changed, was rebased");
+  }
+
   private DraftInput newDraft(String path, int line, String message) {
     DraftInput d = new DraftInput();
     d.path = path;
diff --git a/javatests/com/google/gerrit/acceptance/git/GitOverHttpServletIT.java b/javatests/com/google/gerrit/acceptance/git/GitOverHttpServletIT.java
index 42e046a..90f4134 100644
--- a/javatests/com/google/gerrit/acceptance/git/GitOverHttpServletIT.java
+++ b/javatests/com/google/gerrit/acceptance/git/GitOverHttpServletIT.java
@@ -17,7 +17,9 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import com.google.gerrit.server.AuditEvent;
+import com.google.gerrit.server.audit.HttpAuditEvent;
 import java.util.Collections;
+import javax.servlet.http.HttpServletResponse;
 import org.eclipse.jgit.transport.CredentialsProvider;
 import org.eclipse.jgit.transport.RefSpec;
 import org.eclipse.jgit.transport.UsernamePasswordCredentialsProvider;
@@ -25,6 +27,7 @@
 import org.junit.Test;
 
 public class GitOverHttpServletIT extends AbstractPushForReview {
+  private static final long AUDIT_EVENT_TIMEOUT = 500L;
 
   @Before
   public void beforeEach() throws Exception {
@@ -42,6 +45,7 @@
         .setRemote("origin")
         .setRefSpecs(new RefSpec("HEAD:refs/for/master"))
         .call();
+    waitForAudit();
 
     // Git smart protocol makes two requests:
     // https://github.com/git/git/blob/master/Documentation/technical/http-protocol.txt
@@ -51,11 +55,13 @@
     assertThat(e.who.getAccountId()).isEqualTo(admin.id);
     assertThat(e.what).endsWith("/git-receive-pack");
     assertThat(e.params).isEmpty();
+    assertThat(((HttpAuditEvent) e).httpStatus).isEqualTo(HttpServletResponse.SC_OK);
   }
 
   @Test
   public void uploadPackAuditEventLog() throws Exception {
     testRepo.git().fetch().call();
+    waitForAudit();
 
     assertThat(auditService.auditEvents.size()).isEqualTo(1);
 
@@ -64,5 +70,12 @@
     assertThat(e.params.get("service"))
         .containsExactlyElementsIn(Collections.singletonList("git-upload-pack"));
     assertThat(e.what).endsWith("service=git-upload-pack");
+    assertThat(((HttpAuditEvent) e).httpStatus).isEqualTo(HttpServletResponse.SC_OK);
+  }
+
+  private void waitForAudit() throws InterruptedException {
+    synchronized (auditService.auditEvents) {
+      auditService.auditEvents.wait(AUDIT_EVENT_TIMEOUT);
+    }
   }
 }
diff --git a/javatests/com/google/gerrit/util/http/RequestUtilTest.java b/javatests/com/google/gerrit/util/http/RequestUtilTest.java
index 0bf34e7..adda5e7 100644
--- a/javatests/com/google/gerrit/util/http/RequestUtilTest.java
+++ b/javatests/com/google/gerrit/util/http/RequestUtilTest.java
@@ -15,6 +15,8 @@
 package com.google.gerrit.util.http;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.gerrit.util.http.RequestUtil.getEncodedPathInfo;
+import static com.google.gerrit.util.http.RequestUtil.getRestPathWithoutIds;
 
 import com.google.gerrit.testing.GerritBaseTests;
 import com.google.gerrit.util.http.testutil.FakeHttpServletRequest;
@@ -22,36 +24,45 @@
 
 public class RequestUtilTest extends GerritBaseTests {
   @Test
-  public void emptyContextPath() {
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("", "/s", "/foo/bar")))
-        .isEqualTo("/foo/bar");
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("", "/s", "/foo%2Fbar")))
-        .isEqualTo("/foo%2Fbar");
+  public void getEncodedPathInfo_emptyContextPath() {
+    assertThat(getEncodedPathInfo(fakeRequest("", "/s", "/foo/bar"))).isEqualTo("/foo/bar");
+    assertThat(getEncodedPathInfo(fakeRequest("", "/s", "/foo%2Fbar"))).isEqualTo("/foo%2Fbar");
   }
 
   @Test
-  public void emptyServletPath() {
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("", "/c", "/foo/bar")))
-        .isEqualTo("/foo/bar");
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("", "/c", "/foo%2Fbar")))
-        .isEqualTo("/foo%2Fbar");
+  public void getEncodedPathInfo_emptyServletPath() {
+    assertThat(getEncodedPathInfo(fakeRequest("", "/c", "/foo/bar"))).isEqualTo("/foo/bar");
+    assertThat(getEncodedPathInfo(fakeRequest("", "/c", "/foo%2Fbar"))).isEqualTo("/foo%2Fbar");
   }
 
   @Test
-  public void trailingSlashes() {
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("/c", "/s", "/foo/bar/")))
-        .isEqualTo("/foo/bar/");
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("/c", "/s", "/foo/bar///")))
-        .isEqualTo("/foo/bar/");
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("/c", "/s", "/foo%2Fbar/")))
-        .isEqualTo("/foo%2Fbar/");
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("/c", "/s", "/foo%2Fbar///")))
+  public void getEncodedPathInfo_trailingSlashes() {
+    assertThat(getEncodedPathInfo(fakeRequest("/c", "/s", "/foo/bar/"))).isEqualTo("/foo/bar/");
+    assertThat(getEncodedPathInfo(fakeRequest("/c", "/s", "/foo/bar///"))).isEqualTo("/foo/bar/");
+    assertThat(getEncodedPathInfo(fakeRequest("/c", "/s", "/foo%2Fbar/"))).isEqualTo("/foo%2Fbar/");
+    assertThat(getEncodedPathInfo(fakeRequest("/c", "/s", "/foo%2Fbar///")))
         .isEqualTo("/foo%2Fbar/");
   }
 
   @Test
   public void emptyPathInfo() {
-    assertThat(RequestUtil.getEncodedPathInfo(fakeRequest("/c", "/s", ""))).isNull();
+    assertThat(getEncodedPathInfo(fakeRequest("/c", "/s", ""))).isNull();
+  }
+
+  @Test
+  public void getRestPathWithoutIds_emptyContextPath() {
+    assertThat(getRestPathWithoutIds(fakeRequest("", "/a/accounts", "/123/test")))
+        .isEqualTo("/accounts/test");
+    assertThat(getRestPathWithoutIds(fakeRequest("", "/accounts", "/123/test")))
+        .isEqualTo("/accounts/test");
+  }
+
+  @Test
+  public void getRestPathWithoutIds_nonEmptyContextPath() {
+    assertThat(getRestPathWithoutIds(fakeRequest("/c", "/a/accounts", "/123/test")))
+        .isEqualTo("/accounts/test");
+    assertThat(getRestPathWithoutIds(fakeRequest("/c", "/accounts", "/123/test")))
+        .isEqualTo("/accounts/test");
   }
 
   private FakeHttpServletRequest fakeRequest(