diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index a8eb875..16dd9b2 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -874,6 +874,12 @@
 away from the defaults. The cache may be persisted by setting
 `diskLimit`, which is only recommended if cold start performance is
 problematic.
++
+`external_ids_map` supports computing the new cache value based on a
+previously cached state. This applies modifications based on the Git
+diff and is almost always faster.
+`cache.external_ids_map.enablePartialReloads` turns this behavior on
+or off. The default is `false`.
 
 cache `"git_tags"`::
 +
diff --git a/Documentation/dev-plugins.txt b/Documentation/dev-plugins.txt
index c8ea869..e292549 100644
--- a/Documentation/dev-plugins.txt
+++ b/Documentation/dev-plugins.txt
@@ -2451,40 +2451,6 @@
 Disabled plugins can be re-enabled using the
 link:cmd-plugin-enable.html[plugin enable] command.
 
-== Known issues and bugs
-
-=== Error handling in UI when using the REST API
-
-When a plugin invokes a REST endpoint in the UI, it provides an
-`AsyncCallback` to handle the result. At the moment the
-`onFailure(Throwable)` of the callback is never invoked, even if there
-is an error. Errors are always handled by the Gerrit core UI which
-shows the error dialog. This means currently plugins cannot do any
-error handling and e.g. ignore expected errors.
-
-In the following example the REST endpoint would return '404 Not
-Found' if the user has no username and the Gerrit core UI would
-display an error dialog for this. However having no username is
-not an error and the plugin may like to handle this case.
-
-[source,java]
-----
-new RestApi("accounts").id("self").view("username")
-    .get(new AsyncCallback<NativeString>() {
-
-  @Override
-  public void onSuccess(NativeString username) {
-    // TODO
-  }
-
-  @Override
-  public void onFailure(Throwable caught) {
-    // never invoked
-  }
-});
-----
-
-
 [[reviewer-suggestion]]
 == Reviewer Suggestion Plugins
 
diff --git a/Documentation/intro-gerrit-walkthrough.txt b/Documentation/intro-gerrit-walkthrough.txt
index 1fba1dc..b4f799c2 100644
--- a/Documentation/intro-gerrit-walkthrough.txt
+++ b/Documentation/intro-gerrit-walkthrough.txt
@@ -28,7 +28,7 @@
 modify. To get this code, he runs the following `git clone` command:
 
 ----
-clone ssh://gerrithost:29418/RecipeBook.git RecipeBook
+git clone ssh://gerrithost:29418/RecipeBook.git RecipeBook
 ----
 
 After he clones the repository, he runs a couple of commands to add a
diff --git a/Documentation/metrics.txt b/Documentation/metrics.txt
index 49bed97..63cbd7c 100644
--- a/Documentation/metrics.txt
+++ b/Documentation/metrics.txt
@@ -138,6 +138,10 @@
 * `notedb/stage_update_latency`: Latency for staging updates to NoteDb by table.
 * `notedb/read_latency`: NoteDb read latency by table.
 * `notedb/parse_latency`: NoteDb parse latency by table.
+* `notedb/external_id_cache_load_count`: Total number of times the external ID
+  cache loader was called.
+* `notedb/external_id_partial_read_latency`: Latency for generating a new external ID
+  cache state from a prior state.
 * `notedb/external_id_update_count`: Total number of external ID updates.
 * `notedb/read_all_external_ids_latency`: Latency for reading all
 external ID's from NoteDb.
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 15f59c1..56376fa 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -849,8 +849,10 @@
 Creates a new patch set with a new commit message.
 
 The new commit message must be provided in the request body inside a
-link:#commit-message-input[CommitMessageInput] entity and contain the change ID footer if
-link:project-configuration.html#require-change-id[Require Change-Id] was specified.
+link:#commit-message-input[CommitMessageInput] entity. If a Change-Id
+footer is specified, it must match the current Change-Id footer. If
+the Change-Id footer is absent, the current Change-Id is added to the
+message.
 
 .Request
 ----
diff --git a/Documentation/rest-api-projects.txt b/Documentation/rest-api-projects.txt
index f69c4ae..76151b4 100644
--- a/Documentation/rest-api-projects.txt
+++ b/Documentation/rest-api-projects.txt
@@ -3058,12 +3058,12 @@
 |Field Name |        |Description
 |`match`    |        |A JavaScript regular expression to match
 positions to be replaced with a hyperlink, as documented in
-link#config-gerrit.html#commentlink.name.match[commentlink.name.match].
+link:config-gerrit.html#commentlink.name.match[commentlink.name.match].
 |`link`     |        |The URL to direct the user to whenever the
 regular expression is matched, as documented in
-link#config-gerrit.html#commentlink.name.link[commentlink.name.link].
+link:config-gerrit.html#commentlink.name.link[commentlink.name.link].
 |`enabled`  |optional|Whether the commentlink is enabled, as documented
-in link#config-gerrit.html#commentlink.name.enabled[
+in link:config-gerrit.html#commentlink.name.enabled[
 commentlink.name.enabled]. If not set the commentlink is enabled.
 |==================================================
 
diff --git a/Documentation/user-inline-edit.txt b/Documentation/user-inline-edit.txt
index f64c449..1f5e195 100644
--- a/Documentation/user-inline-edit.txt
+++ b/Documentation/user-inline-edit.txt
@@ -72,7 +72,7 @@
 
 To add a file to the change:
 
-. In the top left corner of the change, click Edit.
+. In the top right corner of the change, click Edit.
 . Next to Files, click Open:
 
 +
diff --git a/java/com/google/gerrit/extensions/api/changes/HashtagsInput.java b/java/com/google/gerrit/extensions/api/changes/HashtagsInput.java
index 8f66f12..bbc8a2e 100644
--- a/java/com/google/gerrit/extensions/api/changes/HashtagsInput.java
+++ b/java/com/google/gerrit/extensions/api/changes/HashtagsInput.java
@@ -26,4 +26,9 @@
   public HashtagsInput(Set<String> add) {
     this.add = add;
   }
+
+  public HashtagsInput(Set<String> add, Set<String> remove) {
+    this(add);
+    this.remove = remove;
+  }
 }
diff --git a/java/com/google/gerrit/json/BUILD b/java/com/google/gerrit/json/BUILD
index 7282dc4..030dddc 100644
--- a/java/com/google/gerrit/json/BUILD
+++ b/java/com/google/gerrit/json/BUILD
@@ -4,5 +4,6 @@
     visibility = ["//visibility:public"],
     deps = [
         "//lib:gson",
+        "//lib/flogger:api",
     ],
 )
diff --git a/java/com/google/gerrit/json/EnumTypeAdapterFactory.java b/java/com/google/gerrit/json/EnumTypeAdapterFactory.java
new file mode 100644
index 0000000..dc74f67
--- /dev/null
+++ b/java/com/google/gerrit/json/EnumTypeAdapterFactory.java
@@ -0,0 +1,78 @@
+// Copyright (C) 2019 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.json;
+
+import com.google.common.flogger.FluentLogger;
+import com.google.gson.Gson;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.internal.bind.TypeAdapters;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+
+/**
+ * A {@code TypeAdapterFactory} for enums.
+ *
+ * <p>This factory introduces a wrapper around Gson's own default enum handler to add the following
+ * special behavior: log when input which doesn't match any existing enum value is encountered.
+ */
+public class EnumTypeAdapterFactory implements TypeAdapterFactory {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  @SuppressWarnings({"unchecked"})
+  @Override
+  public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
+    TypeAdapter<T> defaultEnumAdapter = TypeAdapters.ENUM_FACTORY.create(gson, typeToken);
+    if (defaultEnumAdapter == null) {
+      // Not an enum. -> Enum type adapter doesn't apply.
+      return null;
+    }
+
+    return (TypeAdapter<T>) new EnumTypeAdapter(defaultEnumAdapter, typeToken);
+  }
+
+  private static class EnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
+
+    private final TypeAdapter<T> defaultEnumAdapter;
+    private final TypeToken<T> typeToken;
+
+    public EnumTypeAdapter(TypeAdapter<T> defaultEnumAdapter, TypeToken<T> typeToken) {
+      this.defaultEnumAdapter = defaultEnumAdapter;
+      this.typeToken = typeToken;
+    }
+
+    @Override
+    public T read(JsonReader in) throws IOException {
+      // Still handle null values. -> Check them first.
+      if (in.peek() == JsonToken.NULL) {
+        in.nextNull();
+        return null;
+      }
+      T enumValue = defaultEnumAdapter.read(in);
+      if (enumValue == null) {
+        logger.atWarning().log("Expected an existing value for enum %s.", typeToken);
+      }
+      return enumValue;
+    }
+
+    @Override
+    public void write(JsonWriter out, T value) throws IOException {
+      defaultEnumAdapter.write(out, value);
+    }
+  }
+}
diff --git a/java/com/google/gerrit/json/OutputFormat.java b/java/com/google/gerrit/json/OutputFormat.java
index a2d174f..3e7c319 100644
--- a/java/com/google/gerrit/json/OutputFormat.java
+++ b/java/com/google/gerrit/json/OutputFormat.java
@@ -55,7 +55,8 @@
     GsonBuilder gb =
         new GsonBuilder()
             .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
-            .registerTypeAdapter(Timestamp.class, new SqlTimestampDeserializer());
+            .registerTypeAdapter(Timestamp.class, new SqlTimestampDeserializer())
+            .registerTypeAdapterFactory(new EnumTypeAdapterFactory());
     if (this == OutputFormat.JSON) {
       gb.setPrettyPrinting();
     }
diff --git a/java/com/google/gerrit/server/BUILD b/java/com/google/gerrit/server/BUILD
index 2cc4fb2..6d4dfcf 100644
--- a/java/com/google/gerrit/server/BUILD
+++ b/java/com/google/gerrit/server/BUILD
@@ -8,6 +8,11 @@
     "config/GerritGlobalModule.java",
 ]
 
+TESTING_SRC = [
+    "account/externalids/testing/ExternalIdInserter.java",
+    "account/externalids/testing/ExternalIdTestUtil.java",
+]
+
 java_library(
     name = "constants",
     srcs = CONSTANTS_SRC,
@@ -24,7 +29,7 @@
     name = "server",
     srcs = glob(
         ["**/*.java"],
-        exclude = CONSTANTS_SRC + GERRIT_GLOBAL_MODULE_SRC,
+        exclude = CONSTANTS_SRC + GERRIT_GLOBAL_MODULE_SRC + TESTING_SRC,
     ),
     resource_strip_prefix = "resources",
     resources = ["//resources/com/google/gerrit/server"],
diff --git a/java/com/google/gerrit/server/account/AccountManager.java b/java/com/google/gerrit/server/account/AccountManager.java
index 7fb9997..09757eb 100644
--- a/java/com/google/gerrit/server/account/AccountManager.java
+++ b/java/com/google/gerrit/server/account/AccountManager.java
@@ -15,6 +15,7 @@
 package com.google.gerrit.server.account;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_USERNAME;
 
 import com.google.common.base.Strings;
@@ -448,8 +449,10 @@
             "Delete External IDs on Update Link",
             to,
             (a, u) -> {
-              Collection<ExternalId> filteredExtIdsByScheme =
-                  a.getExternalIds(who.getExternalIdKey().scheme());
+              Set<ExternalId> filteredExtIdsByScheme =
+                  a.getExternalIds().stream()
+                      .filter(e -> e.key().isScheme(who.getExternalIdKey().scheme()))
+                      .collect(toImmutableSet());
               if (filteredExtIdsByScheme.isEmpty()) {
                 return;
               }
diff --git a/java/com/google/gerrit/server/account/AccountState.java b/java/com/google/gerrit/server/account/AccountState.java
index 4a04f01..8555166 100644
--- a/java/com/google/gerrit/server/account/AccountState.java
+++ b/java/com/google/gerrit/server/account/AccountState.java
@@ -14,13 +14,10 @@
 
 package com.google.gerrit.server.account;
 
-import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_USERNAME;
 
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Strings;
-import com.google.common.cache.Cache;
-import com.google.common.cache.CacheBuilder;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.flogger.FluentLogger;
@@ -29,8 +26,6 @@
 import com.google.gerrit.extensions.client.EditPreferencesInfo;
 import com.google.gerrit.extensions.client.GeneralPreferencesInfo;
 import com.google.gerrit.reviewdb.client.Account;
-import com.google.gerrit.server.CurrentUser.PropertyKey;
-import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.account.ProjectWatches.NotifyType;
 import com.google.gerrit.server.account.ProjectWatches.ProjectWatchKey;
 import com.google.gerrit.server.account.externalids.ExternalId;
@@ -146,7 +141,6 @@
   private final GeneralPreferencesInfo generalPreferences;
   private final DiffPreferencesInfo diffPreferences;
   private final EditPreferencesInfo editPreferences;
-  private Cache<IdentifiedUser.PropertyKey<Object>, Object> properties;
 
   private AccountState(
       Account account,
@@ -209,11 +203,6 @@
     return externalIds;
   }
 
-  /** The external identities that identify the account holder that match the given scheme. */
-  public ImmutableSet<ExternalId> getExternalIds(String scheme) {
-    return externalIds.stream().filter(e -> e.key().isScheme(scheme)).collect(toImmutableSet());
-  }
-
   /** The project watches of the account. */
   public ImmutableMap<ProjectWatchKey, ImmutableSet<NotifyType>> getProjectWatches() {
     return projectWatches;
@@ -234,61 +223,6 @@
     return editPreferences;
   }
 
-  /**
-   * Lookup a previously stored property.
-   *
-   * <p>All properties are automatically cleared when the account cache invalidates the {@code
-   * AccountState}. This method is thread-safe.
-   *
-   * @param key unique property key.
-   * @return previously stored value, or {@code null}.
-   */
-  @Nullable
-  public <T> T get(PropertyKey<T> key) {
-    Cache<PropertyKey<Object>, Object> p = properties(false);
-    if (p != null) {
-      @SuppressWarnings("unchecked")
-      T value = (T) p.getIfPresent(key);
-      return value;
-    }
-    return null;
-  }
-
-  /**
-   * Store a property for later retrieval.
-   *
-   * <p>This method is thread-safe.
-   *
-   * @param key unique property key.
-   * @param value value to store; or {@code null} to clear the value.
-   */
-  public <T> void put(PropertyKey<T> key, @Nullable T value) {
-    Cache<PropertyKey<Object>, Object> p = properties(value != null);
-    if (p != null) {
-      @SuppressWarnings("unchecked")
-      PropertyKey<Object> k = (PropertyKey<Object>) key;
-      if (value != null) {
-        p.put(k, value);
-      } else {
-        p.invalidate(k);
-      }
-    }
-  }
-
-  private synchronized Cache<PropertyKey<Object>, Object> properties(boolean allocate) {
-    if (properties == null && allocate) {
-      properties =
-          CacheBuilder.newBuilder()
-              .concurrencyLevel(1)
-              .initialCapacity(16)
-              // Use weakKeys to ensure plugins that garbage collect will also
-              // eventually release data held in any still live AccountState.
-              .weakKeys()
-              .build();
-    }
-    return properties;
-  }
-
   @Override
   public String toString() {
     MoreObjects.ToStringHelper h = MoreObjects.toStringHelper(this);
diff --git a/java/com/google/gerrit/server/account/externalids/ExternalIdCacheImpl.java b/java/com/google/gerrit/server/account/externalids/ExternalIdCacheImpl.java
index 25fca4d..35c4c98 100644
--- a/java/com/google/gerrit/server/account/externalids/ExternalIdCacheImpl.java
+++ b/java/com/google/gerrit/server/account/externalids/ExternalIdCacheImpl.java
@@ -14,17 +14,12 @@
 
 package com.google.gerrit.server.account.externalids;
 
-import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
-import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
 import com.google.common.collect.MultimapBuilder;
 import com.google.common.collect.SetMultimap;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.reviewdb.client.Account;
-import com.google.gerrit.server.logging.Metadata;
-import com.google.gerrit.server.logging.TraceContext;
-import com.google.gerrit.server.logging.TraceContext.TraceTimer;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import com.google.inject.name.Named;
@@ -147,24 +142,4 @@
       lock.unlock();
     }
   }
-
-  static class Loader extends CacheLoader<ObjectId, AllExternalIds> {
-    private final ExternalIdReader externalIdReader;
-
-    @Inject
-    Loader(ExternalIdReader externalIdReader) {
-      this.externalIdReader = externalIdReader;
-    }
-
-    @Override
-    public AllExternalIds load(ObjectId notesRev) throws Exception {
-      try (TraceTimer timer =
-          TraceContext.newTimer(
-              "Loading external IDs", Metadata.builder().revision(notesRev.name()).build())) {
-        ImmutableSet<ExternalId> externalIds = externalIdReader.all(notesRev);
-        externalIds.forEach(ExternalId::checkThatBlobIdIsSet);
-        return AllExternalIds.create(externalIds);
-      }
-    }
-  }
 }
diff --git a/java/com/google/gerrit/server/account/externalids/ExternalIdCacheLoader.java b/java/com/google/gerrit/server/account/externalids/ExternalIdCacheLoader.java
new file mode 100644
index 0000000..68841da
--- /dev/null
+++ b/java/com/google/gerrit/server/account/externalids/ExternalIdCacheLoader.java
@@ -0,0 +1,271 @@
+// Copyright (C) 2019 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.account.externalids;
+
+import com.google.common.base.CharMatcher;
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheLoader;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSetMultimap;
+import com.google.common.flogger.FluentLogger;
+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.MetricMaker;
+import com.google.gerrit.metrics.Timer0;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.config.AllUsersName;
+import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.logging.Metadata;
+import com.google.gerrit.server.logging.TraceContext;
+import com.google.gerrit.server.logging.TraceContext.TraceTimer;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import com.google.inject.name.Named;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.treewalk.TreeWalk;
+import org.eclipse.jgit.treewalk.filter.TreeFilter;
+
+/** Loads cache values for the external ID cache using either a full or a partial reload. */
+@Singleton
+public class ExternalIdCacheLoader extends CacheLoader<ObjectId, AllExternalIds> {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  // Maximum number of prior states we inspect to find a base for differential. If no cached state
+  // is found within this number of parents, we fall back to reading everything from scratch.
+  private static final int MAX_HISTORY_LOOKBACK = 10;
+
+  private final ExternalIdReader externalIdReader;
+  private final Provider<Cache<ObjectId, AllExternalIds>> externalIdCache;
+  private final GitRepositoryManager gitRepositoryManager;
+  private final AllUsersName allUsersName;
+  private final Counter1<Boolean> reloadCounter;
+  private final Timer0 reloadDifferential;
+  private final boolean enablePartialReloads;
+
+  @Inject
+  ExternalIdCacheLoader(
+      GitRepositoryManager gitRepositoryManager,
+      AllUsersName allUsersName,
+      ExternalIdReader externalIdReader,
+      @Named(ExternalIdCacheImpl.CACHE_NAME)
+          Provider<Cache<ObjectId, AllExternalIds>> externalIdCache,
+      MetricMaker metricMaker,
+      @GerritServerConfig Config config) {
+    this.externalIdReader = externalIdReader;
+    this.externalIdCache = externalIdCache;
+    this.gitRepositoryManager = gitRepositoryManager;
+    this.allUsersName = allUsersName;
+    this.reloadCounter =
+        metricMaker.newCounter(
+            "notedb/external_id_cache_load_count",
+            new Description("Total number of external ID cache reloads from Git.")
+                .setRate()
+                .setUnit("updates"),
+            Field.ofBoolean("partial", Metadata.Builder::partial).build());
+    this.reloadDifferential =
+        metricMaker.newTimer(
+            "notedb/external_id_partial_read_latency",
+            new Description(
+                    "Latency for generating a new external ID cache state from a prior state.")
+                .setCumulative()
+                .setUnit(Units.MILLISECONDS));
+    this.enablePartialReloads =
+        config.getBoolean("cache", ExternalIdCacheImpl.CACHE_NAME, "enablePartialReloads", false);
+  }
+
+  @Override
+  public AllExternalIds load(ObjectId notesRev) throws IOException, ConfigInvalidException {
+    if (!enablePartialReloads) {
+      logger.atInfo().log(
+          "Partial reloads of "
+              + ExternalIdCacheImpl.CACHE_NAME
+              + " disabled. Falling back to full reload.");
+      return reloadAllExternalIds(notesRev);
+    }
+
+    // The requested value was not in the cache (hence, this loader was invoked). Therefore, try to
+    // create this entry from a past value using the minimal amount of Git operations possible to
+    // reduce latency.
+    //
+    // First, try to find the most recent state we have in the cache. Most of the time, this will be
+    // the state before the last update happened, but it can also date further back. We try a best
+    // effort approach and check the last 10 states. If nothing is found, we default to loading the
+    // value from scratch.
+    //
+    // If a prior state was found, we use Git to diff the trees and find modifications. This is
+    // faster than just loading the complete current tree and working off of that because of how the
+    // data is structured: NotesMaps use nested trees, so, for example, a NotesMap with 200k entries
+    // has two layers of nesting: 12/34/1234..99. TreeWalk is smart in skipping the traversal of
+    // identical subtrees.
+    //
+    // Once we know what files changed, we apply additions and removals to the previously cached
+    // state.
+
+    try (Repository repo = gitRepositoryManager.openRepository(allUsersName);
+        RevWalk rw = new RevWalk(repo)) {
+      long start = System.nanoTime();
+      Ref extIdRef = repo.exactRef(RefNames.REFS_EXTERNAL_IDS);
+      if (extIdRef == null) {
+        logger.atInfo().log(
+            RefNames.REFS_EXTERNAL_IDS + " not initialized, falling back to full reload.");
+        return reloadAllExternalIds(notesRev);
+      }
+
+      RevCommit currentCommit = rw.parseCommit(extIdRef.getObjectId());
+      rw.markStart(currentCommit);
+      RevCommit parentWithCacheValue;
+      AllExternalIds oldExternalIds = null;
+      int i = 0;
+      while ((parentWithCacheValue = rw.next()) != null
+          && i++ < MAX_HISTORY_LOOKBACK
+          && parentWithCacheValue.getParentCount() < 2) {
+        oldExternalIds = externalIdCache.get().getIfPresent(parentWithCacheValue.getId());
+        if (oldExternalIds != null) {
+          // We found a previously cached state.
+          break;
+        }
+      }
+      if (oldExternalIds == null) {
+        logger.atWarning().log(
+            "Unable to find an old ExternalId cache state, falling back to full reload");
+        return reloadAllExternalIds(notesRev);
+      }
+
+      // Diff trees to recognize modifications
+      Set<ObjectId> removals = new HashSet<>(); // Set<Blob-Object-Id>
+      Map<ObjectId, ObjectId> additions = new HashMap<>(); // Map<Name-ObjectId, Blob-Object-Id>
+      try (TreeWalk treeWalk = new TreeWalk(repo)) {
+        treeWalk.setFilter(TreeFilter.ANY_DIFF);
+        treeWalk.setRecursive(true);
+        treeWalk.reset(parentWithCacheValue.getTree(), currentCommit.getTree());
+        while (treeWalk.next()) {
+          String path = treeWalk.getPathString();
+          ObjectId oldBlob = treeWalk.getObjectId(0);
+          ObjectId newBlob = treeWalk.getObjectId(1);
+          if (ObjectId.zeroId().equals(newBlob)) {
+            // Deletion
+            removals.add(oldBlob);
+          } else if (ObjectId.zeroId().equals(oldBlob)) {
+            // Addition
+            additions.put(fileNameToObjectId(path), newBlob);
+          } else {
+            // Modification
+            removals.add(oldBlob);
+            additions.put(fileNameToObjectId(path), newBlob);
+          }
+        }
+      }
+
+      AllExternalIds allExternalIds =
+          buildAllExternalIds(repo, oldExternalIds, additions, removals);
+      reloadCounter.increment(true);
+      reloadDifferential.record(System.nanoTime() - start, TimeUnit.NANOSECONDS);
+      return allExternalIds;
+    }
+  }
+
+  private static ObjectId fileNameToObjectId(String path) {
+    return ObjectId.fromString(CharMatcher.is('/').removeFrom(path));
+  }
+
+  /**
+   * Build a new {@link AllExternalIds} from an old state by applying additions and removals that
+   * were performed since then.
+   *
+   * <p>Removals are applied before additions.
+   *
+   * @param repo open repository
+   * @param oldExternalIds prior state that is used as base
+   * @param additions map of name to blob ID for each external ID that should be added
+   * @param removals set of name {@link ObjectId}s that should be removed
+   */
+  private static AllExternalIds buildAllExternalIds(
+      Repository repo,
+      AllExternalIds oldExternalIds,
+      Map<ObjectId, ObjectId> additions,
+      Set<ObjectId> removals)
+      throws IOException {
+    ImmutableSetMultimap.Builder<Account.Id, ExternalId> byAccount = ImmutableSetMultimap.builder();
+    ImmutableSetMultimap.Builder<String, ExternalId> byEmail = ImmutableSetMultimap.builder();
+
+    // Copy over old ExternalIds but exclude deleted ones
+    for (ExternalId externalId : oldExternalIds.byAccount().values()) {
+      if (removals.contains(externalId.blobId())) {
+        continue;
+      }
+
+      byAccount.put(externalId.accountId(), externalId);
+      if (externalId.email() != null) {
+        byEmail.put(externalId.email(), externalId);
+      }
+    }
+
+    // Add newly discovered ExternalIds
+    try (ObjectReader reader = repo.newObjectReader()) {
+      for (Map.Entry<ObjectId, ObjectId> nameToBlob : additions.entrySet()) {
+        ExternalId parsedExternalId;
+        try {
+          parsedExternalId =
+              ExternalId.parse(
+                  nameToBlob.getKey().name(),
+                  reader.open(nameToBlob.getValue()).getCachedBytes(),
+                  nameToBlob.getValue());
+        } catch (ConfigInvalidException | RuntimeException e) {
+          logger.atSevere().withCause(e).log(
+              "Ignoring invalid external ID note %s", nameToBlob.getKey().name());
+          continue;
+        }
+
+        byAccount.put(parsedExternalId.accountId(), parsedExternalId);
+        if (parsedExternalId.email() != null) {
+          byEmail.put(parsedExternalId.email(), parsedExternalId);
+        }
+      }
+    }
+    return new AutoValue_AllExternalIds(byAccount.build(), byEmail.build());
+  }
+
+  private AllExternalIds reloadAllExternalIds(ObjectId notesRev)
+      throws IOException, ConfigInvalidException {
+    try (TraceTimer ignored =
+        TraceContext.newTimer(
+            "Loading external IDs from scratch",
+            Metadata.builder().revision(notesRev.name()).build())) {
+      ImmutableSet<ExternalId> externalIds = externalIdReader.all(notesRev);
+      externalIds.forEach(ExternalId::checkThatBlobIdIsSet);
+      AllExternalIds allExternalIds = AllExternalIds.create(externalIds);
+      reloadCounter.increment(false);
+      return allExternalIds;
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/account/externalids/ExternalIdModule.java b/java/com/google/gerrit/server/account/externalids/ExternalIdModule.java
index fc311e7..3e5d7b8 100644
--- a/java/com/google/gerrit/server/account/externalids/ExternalIdModule.java
+++ b/java/com/google/gerrit/server/account/externalids/ExternalIdModule.java
@@ -14,7 +14,6 @@
 
 package com.google.gerrit.server.account.externalids;
 
-import com.google.gerrit.server.account.externalids.ExternalIdCacheImpl.Loader;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.cache.serialize.ObjectIdCacheSerializer;
 import com.google.inject.TypeLiteral;
@@ -31,9 +30,12 @@
         // from the cache. Extend the cache size by 1 to cover this case, but expire the extra
         // object after a short period of time, since it may be a potentially large amount of
         // memory.
+        // When loading a new value because the primary data advanced, we want to leverage the old
+        // cache state to recompute only what changed. This doesn't affect cache size though as
+        // Guava calls the loader first and evicts later on.
         .maximumWeight(2)
         .expireFromMemoryAfterAccess(Duration.ofMinutes(1))
-        .loader(Loader.class)
+        .loader(ExternalIdCacheLoader.class)
         .diskLimit(-1)
         .version(1)
         .keySerializer(ObjectIdCacheSerializer.INSTANCE)
diff --git a/java/com/google/gerrit/server/account/externalids/testing/BUILD b/java/com/google/gerrit/server/account/externalids/testing/BUILD
new file mode 100644
index 0000000..ec98ec8
--- /dev/null
+++ b/java/com/google/gerrit/server/account/externalids/testing/BUILD
@@ -0,0 +1,11 @@
+java_library(
+    name = "testing",
+    testonly = 1,
+    srcs = glob(["**/*.java"]),
+    visibility = ["//visibility:public"],
+    deps = [
+        "//java/com/google/gerrit/reviewdb:server",
+        "//java/com/google/gerrit/server",
+        "//lib/jgit/org.eclipse.jgit:jgit",
+    ],
+)
diff --git a/java/com/google/gerrit/server/account/externalids/testing/ExternalIdInserter.java b/java/com/google/gerrit/server/account/externalids/testing/ExternalIdInserter.java
new file mode 100644
index 0000000..a93192a
--- /dev/null
+++ b/java/com/google/gerrit/server/account/externalids/testing/ExternalIdInserter.java
@@ -0,0 +1,25 @@
+// Copyright (C) 2019 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.account.externalids.testing;
+
+import java.io.IOException;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.notes.NoteMap;
+
+@FunctionalInterface
+public interface ExternalIdInserter {
+  public ObjectId addNote(ObjectInserter ins, NoteMap noteMap) throws IOException;
+}
diff --git a/java/com/google/gerrit/server/account/externalids/testing/ExternalIdTestUtil.java b/java/com/google/gerrit/server/account/externalids/testing/ExternalIdTestUtil.java
new file mode 100644
index 0000000..97fff60
--- /dev/null
+++ b/java/com/google/gerrit/server/account/externalids/testing/ExternalIdTestUtil.java
@@ -0,0 +1,163 @@
+// Copyright (C) 2019 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.account.externalids.testing;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
+import static org.eclipse.jgit.lib.Constants.OBJ_TREE;
+
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.account.externalids.ExternalId;
+import com.google.gerrit.server.account.externalids.ExternalIdReader;
+import java.io.IOException;
+import org.eclipse.jgit.lib.CommitBuilder;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectInserter;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.RefUpdate;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.notes.NoteMap;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+/** Common methods for dealing with external IDs in tests. */
+public class ExternalIdTestUtil {
+
+  public static String insertExternalIdWithoutAccountId(
+      Repository repo, RevWalk rw, PersonIdent ident, Account.Id accountId, String externalId)
+      throws IOException {
+    return insertExternalId(
+        repo,
+        rw,
+        ident,
+        (ins, noteMap) -> {
+          ExternalId extId = ExternalId.create(ExternalId.Key.parse(externalId), accountId);
+          ObjectId noteId = extId.key().sha1();
+          Config c = new Config();
+          extId.writeToConfig(c);
+          c.unset("externalId", extId.key().get(), "accountId");
+          byte[] raw = c.toText().getBytes(UTF_8);
+          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
+          noteMap.set(noteId, dataBlob);
+          return noteId;
+        });
+  }
+
+  public static String insertExternalIdWithKeyThatDoesntMatchNoteId(
+      Repository repo, RevWalk rw, PersonIdent ident, Account.Id accountId, String externalId)
+      throws IOException {
+    return insertExternalId(
+        repo,
+        rw,
+        ident,
+        (ins, noteMap) -> {
+          ExternalId extId = ExternalId.create(ExternalId.Key.parse(externalId), accountId);
+          ObjectId noteId = ExternalId.Key.parse(externalId + "x").sha1();
+          Config c = new Config();
+          extId.writeToConfig(c);
+          byte[] raw = c.toText().getBytes(UTF_8);
+          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
+          noteMap.set(noteId, dataBlob);
+          return noteId;
+        });
+  }
+
+  public static String insertExternalIdWithInvalidConfig(
+      Repository repo, RevWalk rw, PersonIdent ident, String externalId) throws IOException {
+    return insertExternalId(
+        repo,
+        rw,
+        ident,
+        (ins, noteMap) -> {
+          ObjectId noteId = ExternalId.Key.parse(externalId).sha1();
+          byte[] raw = "bad-config".getBytes(UTF_8);
+          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
+          noteMap.set(noteId, dataBlob);
+          return noteId;
+        });
+  }
+
+  public static String insertExternalIdWithEmptyNote(
+      Repository repo, RevWalk rw, PersonIdent ident, String externalId) throws IOException {
+    return insertExternalId(
+        repo,
+        rw,
+        ident,
+        (ins, noteMap) -> {
+          ObjectId noteId = ExternalId.Key.parse(externalId).sha1();
+          byte[] raw = "".getBytes(UTF_8);
+          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
+          noteMap.set(noteId, dataBlob);
+          return noteId;
+        });
+  }
+
+  private static String insertExternalId(
+      Repository repo, RevWalk rw, PersonIdent ident, ExternalIdInserter extIdInserter)
+      throws IOException {
+    ObjectId rev = ExternalIdReader.readRevision(repo);
+    NoteMap noteMap = ExternalIdReader.readNoteMap(rw, rev);
+
+    try (ObjectInserter ins = repo.newObjectInserter()) {
+      ObjectId noteId = extIdInserter.addNote(ins, noteMap);
+
+      CommitBuilder cb = new CommitBuilder();
+      cb.setMessage("Update external IDs");
+      cb.setTreeId(noteMap.writeTree(ins));
+      cb.setAuthor(ident);
+      cb.setCommitter(ident);
+      if (!rev.equals(ObjectId.zeroId())) {
+        cb.setParentId(rev);
+      } else {
+        cb.setParentIds(); // Ref is currently nonexistent, commit has no parents.
+      }
+      if (cb.getTreeId() == null) {
+        if (rev.equals(ObjectId.zeroId())) {
+          cb.setTreeId(ins.insert(OBJ_TREE, new byte[] {})); // No parent, assume empty tree.
+        } else {
+          RevCommit p = rw.parseCommit(rev);
+          cb.setTreeId(p.getTree()); // Copy tree from parent.
+        }
+      }
+      ObjectId commitId = ins.insert(cb);
+      ins.flush();
+
+      RefUpdate u = repo.updateRef(RefNames.REFS_EXTERNAL_IDS);
+      u.setExpectedOldObjectId(rev);
+      u.setNewObjectId(commitId);
+      RefUpdate.Result res = u.update();
+      switch (res) {
+        case NEW:
+        case FAST_FORWARD:
+        case NO_CHANGE:
+        case RENAMED:
+        case FORCED:
+          break;
+        case LOCK_FAILURE:
+        case IO_FAILURE:
+        case NOT_ATTEMPTED:
+        case REJECTED:
+        case REJECTED_CURRENT_BRANCH:
+        case REJECTED_MISSING_OBJECT:
+        case REJECTED_OTHER_REASON:
+        default:
+          throw new IOException("Updating external IDs failed with " + res);
+      }
+      return noteId.getName();
+    }
+  }
+}
diff --git a/java/com/google/gerrit/server/change/ChangeETagComputation.java b/java/com/google/gerrit/server/change/ChangeETagComputation.java
index 5f03200..463989b 100644
--- a/java/com/google/gerrit/server/change/ChangeETagComputation.java
+++ b/java/com/google/gerrit/server/change/ChangeETagComputation.java
@@ -50,6 +50,11 @@
    * <p><strong>Note:</strong> Change ETags are computed very frequently and the computation must be
    * cheap. Take good care to not perform any expensive computations when implementing this.
    *
+   * <p>If an error is encountered during the ETag computation the plugin can indicate this by
+   * throwing any RuntimeException. In this case no value will be included in the change ETag
+   * computation. This means if the error is transient, the ETag will differ when the computation
+   * succeeds on a follow-up run.
+   *
    * @param projectName the name of the project that contains the change
    * @param changeId ID of the change for which the ETag should be computed
    * @return the ETag
diff --git a/java/com/google/gerrit/server/change/ChangeResource.java b/java/com/google/gerrit/server/change/ChangeResource.java
index bb0040d..d8d82c6 100644
--- a/java/com/google/gerrit/server/change/ChangeResource.java
+++ b/java/com/google/gerrit/server/change/ChangeResource.java
@@ -197,6 +197,14 @@
     for (ProjectState p : projectStateTree) {
       hashObjectId(h, p.getConfig().getRevision(), buf);
     }
+
+    changeETagComputation.runEach(
+        c -> {
+          String pluginETag = c.getETag(notes.getProjectName(), notes.getChangeId());
+          if (pluginETag != null) {
+            h.putString(pluginETag, UTF_8);
+          }
+        });
   }
 
   @Override
@@ -206,13 +214,6 @@
       h.putString(starredChangesUtil.getObjectId(user.getAccountId(), getId()).name(), UTF_8);
     }
     prepareETag(h, user);
-    changeETagComputation.runEach(
-        c -> {
-          String pluginETag = c.getETag(notes.getProjectName(), notes.getChangeId());
-          if (pluginETag != null) {
-            h.putString(pluginETag, UTF_8);
-          }
-        });
     return h.hash().toString();
   }
 
diff --git a/java/com/google/gerrit/server/git/receive/ReplaceOp.java b/java/com/google/gerrit/server/git/receive/ReplaceOp.java
index 5e1f178..a9a49bf 100644
--- a/java/com/google/gerrit/server/git/receive/ReplaceOp.java
+++ b/java/com/google/gerrit/server/git/receive/ReplaceOp.java
@@ -481,11 +481,7 @@
     change.setCurrentPatchSet(info);
 
     List<String> idList = commit.getFooterLines(CHANGE_ID);
-    if (idList.isEmpty()) {
-      change.setKey(Change.key("I" + commitId.name()));
-    } else {
-      change.setKey(Change.key(idList.get(idList.size() - 1).trim()));
-    }
+    change.setKey(Change.key(idList.get(idList.size() - 1).trim()));
   }
 
   private List<Comment> publishComments(ChangeContext ctx, boolean workInProgress) {
diff --git a/java/com/google/gerrit/server/logging/Metadata.java b/java/com/google/gerrit/server/logging/Metadata.java
index 400f48f..7eba4de 100644
--- a/java/com/google/gerrit/server/logging/Metadata.java
+++ b/java/com/google/gerrit/server/logging/Metadata.java
@@ -86,9 +86,12 @@
   // The name of the implementation method.
   public abstract Optional<String> methodName();
 
-  // Boolean: one or more
+  // One or more resources
   public abstract Optional<Boolean> multiple();
 
+  // Partial or full computation
+  public abstract Optional<Boolean> partial();
+
   // Path of a metadata file in NoteDb.
   public abstract Optional<String> noteDbFilePath();
 
@@ -182,6 +185,8 @@
 
     public abstract Builder multiple(boolean multiple);
 
+    public abstract Builder partial(boolean partial);
+
     public abstract Builder noteDbFilePath(@Nullable String noteDbFilePath);
 
     public abstract Builder noteDbRefName(@Nullable String noteDbRefName);
diff --git a/java/com/google/gerrit/server/plugincontext/PluginContext.java b/java/com/google/gerrit/server/plugincontext/PluginContext.java
index 266eb92..90d56c8 100644
--- a/java/com/google/gerrit/server/plugincontext/PluginContext.java
+++ b/java/com/google/gerrit/server/plugincontext/PluginContext.java
@@ -272,7 +272,7 @@
       Throwables.throwIfUnchecked(e);
       pluginMetrics.incrementErrorCount(extension);
       logger.atWarning().withCause(e).log(
-          "Failure in %s of plugin invoke%s", extensionImpl.getClass(), extension.getPluginName());
+          "Failure in %s of plugin %s", extensionImpl.getClass(), extension.getPluginName());
     }
   }
 
diff --git a/java/com/google/gerrit/server/restapi/change/PutMessage.java b/java/com/google/gerrit/server/restapi/change/PutMessage.java
index db02418..f05641f 100644
--- a/java/com/google/gerrit/server/restapi/change/PutMessage.java
+++ b/java/com/google/gerrit/server/restapi/change/PutMessage.java
@@ -111,10 +111,13 @@
     String sanitizedCommitMessage = CommitMessageUtil.checkAndSanitizeCommitMessage(input.message);
 
     ensureCanEditCommitMessage(resource.getNotes());
-    ensureChangeIdIsCorrect(
-        projectCache.checkedGet(resource.getProject()).is(BooleanProjectConfig.REQUIRE_CHANGE_ID),
-        resource.getChange().getKey().get(),
-        sanitizedCommitMessage);
+    sanitizedCommitMessage =
+        ensureChangeIdIsCorrect(
+            projectCache
+                .checkedGet(resource.getProject())
+                .is(BooleanProjectConfig.REQUIRE_CHANGE_ID),
+            resource.getChange().getKey().get(),
+            sanitizedCommitMessage);
 
     try (Repository repository = repositoryManager.openRepository(resource.getProject());
         RevWalk revWalk = new RevWalk(repository);
@@ -193,7 +196,7 @@
     }
   }
 
-  private static void ensureChangeIdIsCorrect(
+  private static String ensureChangeIdIsCorrect(
       boolean requireChangeId, String currentChangeId, String newCommitMessage)
       throws ResourceConflictException, BadRequestException {
     RevCommit revCommit =
@@ -204,14 +207,21 @@
     CommitMessageUtil.checkAndSanitizeCommitMessage(revCommit.getShortMessage());
 
     List<String> changeIdFooters = revCommit.getFooterLines(FooterConstants.CHANGE_ID);
-    if (requireChangeId && changeIdFooters.isEmpty()) {
-      throw new ResourceConflictException("missing Change-Id footer");
-    }
     if (!changeIdFooters.isEmpty() && !changeIdFooters.get(0).equals(currentChangeId)) {
       throw new ResourceConflictException("wrong Change-Id footer");
     }
-    if (changeIdFooters.size() > 1) {
+
+    if (requireChangeId && revCommit.getFooterLines().isEmpty()) {
+      // sanitization always adds '\n' at the end.
+      newCommitMessage += "\n";
+    }
+
+    if (requireChangeId && changeIdFooters.isEmpty()) {
+      newCommitMessage += FooterConstants.CHANGE_ID.getName() + ": " + currentChangeId + "\n";
+    } else if (changeIdFooters.size() > 1) {
       throw new ResourceConflictException("multiple Change-Id footers");
     }
+
+    return newCommitMessage;
   }
 }
diff --git a/java/com/google/gerrit/server/update/RetryHelper.java b/java/com/google/gerrit/server/update/RetryHelper.java
index 695feba..f50f857 100644
--- a/java/com/google/gerrit/server/update/RetryHelper.java
+++ b/java/com/google/gerrit/server/update/RetryHelper.java
@@ -291,7 +291,7 @@
                       .addTag(RequestId.Type.TRACE_ID, "retry-on-failure-" + new RequestId())
                       .forceLogging();
                   logger.atFine().withCause(t).log(
-                      "%s failed, retry with tracing eanbled",
+                      "%s failed, retry with tracing enabled",
                       opts.caller().map(Class::getSimpleName).orElse("N/A"));
                   return true;
                 }
diff --git a/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java b/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
index 5c2f033..be4162e 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
@@ -87,6 +87,7 @@
 import com.google.gerrit.common.data.LabelFunction;
 import com.google.gerrit.common.data.LabelType;
 import com.google.gerrit.common.data.Permission;
+import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.extensions.annotations.Exports;
 import com.google.gerrit.extensions.api.changes.AddReviewerInput;
 import com.google.gerrit.extensions.api.changes.AddReviewerResult;
@@ -2183,6 +2184,24 @@
   }
 
   @Test
+  public void throwingExceptionFromETagComputationDoesNotBreakGerrit() throws Exception {
+    PushOneCommit.Result r = createChange();
+    String oldETag = parseResource(r).getETag();
+
+    RegistrationHandle registrationHandle =
+        changeETagComputations.add(
+            "gerrit",
+            (p, id) -> {
+              throw new StorageException("exception during test");
+            });
+    try {
+      assertThat(parseResource(r).getETag()).isEqualTo(oldETag);
+    } finally {
+      registrationHandle.remove();
+    }
+  }
+
+  @Test
   public void emailNotificationForFileLevelComment() throws Exception {
     String changeId = createChange().getChangeId();
 
@@ -3861,15 +3880,13 @@
   }
 
   @Test
-  public void changeCommitMessageWithNoChangeIdFails() throws Exception {
+  public void changeCommitMessageWithNoChangeIdRetainsChangeID() throws Exception {
     PushOneCommit.Result r = createChange();
     assertThat(getCommitMessage(r.getChangeId()))
         .isEqualTo("test commit\n\nChange-Id: " + r.getChangeId() + "\n");
-    ResourceConflictException thrown =
-        assertThrows(
-            ResourceConflictException.class,
-            () -> gApi.changes().id(r.getChangeId()).setMessage("modified commit\n"));
-    assertThat(thrown).hasMessageThat().contains("missing Change-Id footer");
+    gApi.changes().id(r.getChangeId()).setMessage("modified commit\n");
+    assertThat(getCommitMessage(r.getChangeId()))
+        .isEqualTo("modified commit\n\nChange-Id: " + r.getChangeId() + "\n");
   }
 
   @Test
diff --git a/javatests/com/google/gerrit/acceptance/rest/account/BUILD b/javatests/com/google/gerrit/acceptance/rest/account/BUILD
index 3b46414..17a6053 100644
--- a/javatests/com/google/gerrit/acceptance/rest/account/BUILD
+++ b/javatests/com/google/gerrit/acceptance/rest/account/BUILD
@@ -4,7 +4,10 @@
     srcs = glob(["*IT.java"]),
     group = "rest_account",
     labels = ["rest"],
-    deps = [":util"],
+    deps = [
+        ":util",
+        "//java/com/google/gerrit/server/account/externalids/testing",
+    ],
 )
 
 java_library(
@@ -18,6 +21,7 @@
     deps = [
         "//java/com/google/gerrit/acceptance:lib",
         "//java/com/google/gerrit/reviewdb:server",
+        "//java/com/google/gerrit/server/account/externalids/testing",
         "//lib:junit",
     ],
 )
diff --git a/javatests/com/google/gerrit/acceptance/rest/account/ExternalIdIT.java b/javatests/com/google/gerrit/acceptance/rest/account/ExternalIdIT.java
index ba3c7ea..e9e8b7f 100644
--- a/javatests/com/google/gerrit/acceptance/rest/account/ExternalIdIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/account/ExternalIdIT.java
@@ -16,6 +16,7 @@
 
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth8.assertThat;
+import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.GitUtil.fetch;
 import static com.google.gerrit.acceptance.GitUtil.pushHead;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allow;
@@ -23,12 +24,13 @@
 import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_MAILTO;
 import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_USERNAME;
 import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_UUID;
+import static com.google.gerrit.server.account.externalids.testing.ExternalIdTestUtil.insertExternalIdWithEmptyNote;
+import static com.google.gerrit.server.account.externalids.testing.ExternalIdTestUtil.insertExternalIdWithInvalidConfig;
+import static com.google.gerrit.server.account.externalids.testing.ExternalIdTestUtil.insertExternalIdWithKeyThatDoesntMatchNoteId;
+import static com.google.gerrit.server.account.externalids.testing.ExternalIdTestUtil.insertExternalIdWithoutAccountId;
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
-import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.stream.Collectors.toList;
-import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
-import static org.eclipse.jgit.lib.Constants.OBJ_TREE;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -58,6 +60,7 @@
 import com.google.gerrit.server.account.externalids.ExternalIds;
 import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
 import com.google.gerrit.server.git.meta.MetaDataUpdate;
+import com.google.gerrit.testing.ConfigSuite;
 import com.google.gson.reflect.TypeToken;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
@@ -74,13 +77,8 @@
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
 import org.eclipse.jgit.junit.TestRepository;
-import org.eclipse.jgit.lib.CommitBuilder;
 import org.eclipse.jgit.lib.Config;
-import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.notes.NoteMap;
 import org.eclipse.jgit.revwalk.FooterLine;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevWalk;
@@ -98,6 +96,20 @@
   @Inject private ProjectOperations projectOperations;
   @Inject private RequestScopeOperations requestScopeOperations;
 
+  @ConfigSuite.Default
+  public static Config partialCacheReloadingEnabled() {
+    Config cfg = new Config();
+    cfg.setBoolean("cache", "external_ids_map", "enablePartialReloads", true);
+    return cfg;
+  }
+
+  @ConfigSuite.Config
+  public static Config partialCacheReloadingDisabled() {
+    Config cfg = new Config();
+    cfg.setBoolean("cache", "external_ids_map", "enablePartialReloads", false);
+    return cfg;
+  }
+
   @Test
   public void getExternalIds() throws Exception {
     Collection<ExternalId> expectedIds = getAccountState(user.id()).getExternalIds();
@@ -329,7 +341,11 @@
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     insertExternalIdWithoutAccountId(
-        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), "foo:bar");
+        allUsersRepo.getRepository(),
+        allUsersRepo.getRevWalk(),
+        admin.newIdent(),
+        admin.id(),
+        "foo:bar");
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     allowPushOfExternalIds();
@@ -350,7 +366,11 @@
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     insertExternalIdWithKeyThatDoesntMatchNoteId(
-        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), "foo:bar");
+        allUsersRepo.getRepository(),
+        allUsersRepo.getRevWalk(),
+        admin.newIdent(),
+        admin.id(),
+        "foo:bar");
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     allowPushOfExternalIds();
@@ -370,7 +390,7 @@
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     insertExternalIdWithInvalidConfig(
-        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), "foo:bar");
+        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), admin.newIdent(), "foo:bar");
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     allowPushOfExternalIds();
@@ -390,7 +410,7 @@
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     insertExternalIdWithEmptyNote(
-        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), "foo:bar");
+        allUsersRepo.getRepository(), allUsersRepo.getRevWalk(), admin.newIdent(), "foo:bar");
     allUsersRepo.reset(RefNames.REFS_EXTERNAL_IDS);
 
     allowPushOfExternalIds();
@@ -571,7 +591,8 @@
     try (Repository repo = repoManager.openRepository(allUsers);
         RevWalk rw = new RevWalk(repo)) {
       String externalId = nextId(scheme, i);
-      String noteId = insertExternalIdWithoutAccountId(repo, rw, externalId);
+      String noteId =
+          insertExternalIdWithoutAccountId(repo, rw, admin.newIdent(), admin.id(), externalId);
       expectedProblems.add(
           consistencyError(
               "Invalid external ID config for note '"
@@ -581,7 +602,9 @@
                   + ".accountId' is missing, expected account ID"));
 
       externalId = nextId(scheme, i);
-      noteId = insertExternalIdWithKeyThatDoesntMatchNoteId(repo, rw, externalId);
+      noteId =
+          insertExternalIdWithKeyThatDoesntMatchNoteId(
+              repo, rw, admin.newIdent(), admin.id(), externalId);
       expectedProblems.add(
           consistencyError(
               "Invalid external ID config for note '"
@@ -592,12 +615,12 @@
                   + noteId
                   + "'"));
 
-      noteId = insertExternalIdWithInvalidConfig(repo, rw, nextId(scheme, i));
+      noteId = insertExternalIdWithInvalidConfig(repo, rw, admin.newIdent(), nextId(scheme, i));
       expectedProblems.add(
           consistencyError(
               "Invalid external ID config for note '" + noteId + "': Invalid line in config file"));
 
-      noteId = insertExternalIdWithEmptyNote(repo, rw, nextId(scheme, i));
+      noteId = insertExternalIdWithEmptyNote(repo, rw, admin.newIdent(), nextId(scheme, i));
       expectedProblems.add(
           consistencyError(
               "Invalid external ID config for note '"
@@ -616,123 +639,6 @@
         "password");
   }
 
-  private String insertExternalIdWithoutAccountId(Repository repo, RevWalk rw, String externalId)
-      throws IOException {
-    return insertExternalId(
-        repo,
-        rw,
-        (ins, noteMap) -> {
-          ExternalId extId = ExternalId.create(ExternalId.Key.parse(externalId), admin.id());
-          ObjectId noteId = extId.key().sha1();
-          Config c = new Config();
-          extId.writeToConfig(c);
-          c.unset("externalId", extId.key().get(), "accountId");
-          byte[] raw = c.toText().getBytes(UTF_8);
-          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
-          noteMap.set(noteId, dataBlob);
-          return noteId;
-        });
-  }
-
-  private String insertExternalIdWithKeyThatDoesntMatchNoteId(
-      Repository repo, RevWalk rw, String externalId) throws IOException {
-    return insertExternalId(
-        repo,
-        rw,
-        (ins, noteMap) -> {
-          ExternalId extId = ExternalId.create(ExternalId.Key.parse(externalId), admin.id());
-          ObjectId noteId = ExternalId.Key.parse(externalId + "x").sha1();
-          Config c = new Config();
-          extId.writeToConfig(c);
-          byte[] raw = c.toText().getBytes(UTF_8);
-          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
-          noteMap.set(noteId, dataBlob);
-          return noteId;
-        });
-  }
-
-  private String insertExternalIdWithInvalidConfig(Repository repo, RevWalk rw, String externalId)
-      throws IOException {
-    return insertExternalId(
-        repo,
-        rw,
-        (ins, noteMap) -> {
-          ObjectId noteId = ExternalId.Key.parse(externalId).sha1();
-          byte[] raw = "bad-config".getBytes(UTF_8);
-          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
-          noteMap.set(noteId, dataBlob);
-          return noteId;
-        });
-  }
-
-  private String insertExternalIdWithEmptyNote(Repository repo, RevWalk rw, String externalId)
-      throws IOException {
-    return insertExternalId(
-        repo,
-        rw,
-        (ins, noteMap) -> {
-          ObjectId noteId = ExternalId.Key.parse(externalId).sha1();
-          byte[] raw = "".getBytes(UTF_8);
-          ObjectId dataBlob = ins.insert(OBJ_BLOB, raw);
-          noteMap.set(noteId, dataBlob);
-          return noteId;
-        });
-  }
-
-  private String insertExternalId(Repository repo, RevWalk rw, ExternalIdInserter extIdInserter)
-      throws IOException {
-    ObjectId rev = ExternalIdReader.readRevision(repo);
-    NoteMap noteMap = ExternalIdReader.readNoteMap(rw, rev);
-
-    try (ObjectInserter ins = repo.newObjectInserter()) {
-      ObjectId noteId = extIdInserter.addNote(ins, noteMap);
-
-      CommitBuilder cb = new CommitBuilder();
-      cb.setMessage("Update external IDs");
-      cb.setTreeId(noteMap.writeTree(ins));
-      cb.setAuthor(admin.newIdent());
-      cb.setCommitter(admin.newIdent());
-      if (!rev.equals(ObjectId.zeroId())) {
-        cb.setParentId(rev);
-      } else {
-        cb.setParentIds(); // Ref is currently nonexistent, commit has no parents.
-      }
-      if (cb.getTreeId() == null) {
-        if (rev.equals(ObjectId.zeroId())) {
-          cb.setTreeId(ins.insert(OBJ_TREE, new byte[] {})); // No parent, assume empty tree.
-        } else {
-          RevCommit p = rw.parseCommit(rev);
-          cb.setTreeId(p.getTree()); // Copy tree from parent.
-        }
-      }
-      ObjectId commitId = ins.insert(cb);
-      ins.flush();
-
-      RefUpdate u = repo.updateRef(RefNames.REFS_EXTERNAL_IDS);
-      u.setExpectedOldObjectId(rev);
-      u.setNewObjectId(commitId);
-      RefUpdate.Result res = u.update();
-      switch (res) {
-        case NEW:
-        case FAST_FORWARD:
-        case NO_CHANGE:
-        case RENAMED:
-        case FORCED:
-          break;
-        case LOCK_FAILURE:
-        case IO_FAILURE:
-        case NOT_ATTEMPTED:
-        case REJECTED:
-        case REJECTED_CURRENT_BRANCH:
-        case REJECTED_MISSING_OBJECT:
-        case REJECTED_OTHER_REASON:
-        default:
-          throw new IOException("Updating external IDs failed with " + res);
-      }
-      return noteId.getName();
-    }
-  }
-
   private ExternalId createExternalIdForNonExistingAccount(String externalId) {
     return ExternalId.create(ExternalId.Key.parse(externalId), Account.id(1));
   }
@@ -803,6 +709,8 @@
 
   @Test
   public void byAccountFailIfReadingExternalIdsFails() throws Exception {
+    assume().that(isPartialCacheReloadingEnabled()).isFalse();
+
     try (AutoCloseable ctx = createFailOnLoadContext()) {
       // update external ID branch so that external IDs need to be reloaded
       insertExtIdBehindGerritsBack(ExternalId.create("foo", "bar", admin.id()));
@@ -813,6 +721,8 @@
 
   @Test
   public void byEmailFailIfReadingExternalIdsFails() throws Exception {
+    assume().that(isPartialCacheReloadingEnabled()).isFalse();
+
     try (AutoCloseable ctx = createFailOnLoadContext()) {
       // update external ID branch so that external IDs need to be reloaded
       insertExtIdBehindGerritsBack(ExternalId.create("foo", "bar", admin.id()));
@@ -954,6 +864,10 @@
     }
   }
 
+  private boolean isPartialCacheReloadingEnabled() {
+    return cfg.getBoolean("cache", "external_ids_map", "enablePartialReloads", true);
+  }
+
   private void insertExtId(ExternalId extId) throws Exception {
     accountsUpdateProvider
         .get()
@@ -1038,9 +952,4 @@
     externalIdReader.setFailOnLoad(true);
     return () -> externalIdReader.setFailOnLoad(false);
   }
-
-  @FunctionalInterface
-  private interface ExternalIdInserter {
-    public ObjectId addNote(ObjectInserter ins, NoteMap noteMap) throws IOException;
-  }
 }
diff --git a/javatests/com/google/gerrit/acceptance/rest/change/ActionsIT.java b/javatests/com/google/gerrit/acceptance/rest/change/ActionsIT.java
index 5fb42da..ae212b6 100644
--- a/javatests/com/google/gerrit/acceptance/rest/change/ActionsIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/change/ActionsIT.java
@@ -25,6 +25,7 @@
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.TestProjectInput;
 import com.google.gerrit.acceptance.testsuite.request.RequestScopeOperations;
+import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.extensions.api.changes.ActionVisitor;
 import com.google.gerrit.extensions.api.changes.ReviewInput;
 import com.google.gerrit.extensions.client.ListChangesOption;
@@ -36,6 +37,7 @@
 import com.google.gerrit.extensions.registration.RegistrationHandle;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.PatchSet;
+import com.google.gerrit.server.change.ChangeETagComputation;
 import com.google.gerrit.server.change.RevisionJson;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.testing.ConfigSuite;
@@ -58,6 +60,7 @@
   @Inject private DynamicSet<ActionVisitor> actionVisitors;
   @Inject private RequestScopeOperations requestScopeOperations;
   @Inject private RevisionJson.Factory revisionJsonFactory;
+  @Inject private DynamicSet<ChangeETagComputation> changeETagComputations;
 
   private RegistrationHandle visitorHandle;
 
@@ -206,6 +209,52 @@
   }
 
   @Test
+  public void pluginCanContributeToETagComputation() throws Exception {
+    String change = createChange().getChangeId();
+    String oldETag = getETag(change);
+
+    RegistrationHandle registrationHandle = changeETagComputations.add("gerrit", (p, id) -> "foo");
+    try {
+      assertThat(getETag(change)).isNotEqualTo(oldETag);
+    } finally {
+      registrationHandle.remove();
+    }
+
+    assertThat(getETag(change)).isEqualTo(oldETag);
+  }
+
+  @Test
+  public void returningNullFromETagComputationDoesNotBreakGerrit() throws Exception {
+    String change = createChange().getChangeId();
+    String oldETag = getETag(change);
+
+    RegistrationHandle registrationHandle = changeETagComputations.add("gerrit", (p, id) -> null);
+    try {
+      assertThat(getETag(change)).isEqualTo(oldETag);
+    } finally {
+      registrationHandle.remove();
+    }
+  }
+
+  @Test
+  public void throwingExceptionFromETagComputationDoesNotBreakGerrit() throws Exception {
+    String change = createChange().getChangeId();
+    String oldETag = getETag(change);
+
+    RegistrationHandle registrationHandle =
+        changeETagComputations.add(
+            "gerrit",
+            (p, id) -> {
+              throw new StorageException("exception during test");
+            });
+    try {
+      assertThat(getETag(change)).isEqualTo(oldETag);
+    } finally {
+      registrationHandle.remove();
+    }
+  }
+
+  @Test
   public void revisionActionsTwoChangesInTopic_conflicting() throws Exception {
     String changeId = createChangeWithTopic().getChangeId();
     approve(changeId);
diff --git a/javatests/com/google/gerrit/json/JsonEnumMappingTest.java b/javatests/com/google/gerrit/json/JsonEnumMappingTest.java
new file mode 100644
index 0000000..6e57b01
--- /dev/null
+++ b/javatests/com/google/gerrit/json/JsonEnumMappingTest.java
@@ -0,0 +1,84 @@
+// Copyright (C) 2019 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.json;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.gson.Gson;
+import org.junit.Test;
+
+public class JsonEnumMappingTest {
+
+  // Use the regular, pre-configured Gson object we use throughout the Gerrit server to ensure that
+  // the EnumTypeAdapterFactory is properly set up.
+  private final Gson gson = OutputFormat.JSON.newGson();
+
+  @Test
+  public void nullCanBeWrittenAndParsedBack() {
+    String resultingJson = gson.toJson(null, TestEnum.class);
+    TestEnum value = gson.fromJson(resultingJson, TestEnum.class);
+    assertThat(value).isNull();
+  }
+
+  @Test
+  public void enumValueCanBeWrittenAndParsedBack() {
+    String resultingJson = gson.toJson(TestEnum.ONE, TestEnum.class);
+    TestEnum value = gson.fromJson(resultingJson, TestEnum.class);
+    assertThat(value).isEqualTo(TestEnum.ONE);
+  }
+
+  @Test
+  public void enumValueCanBeParsed() {
+    TestData data = gson.fromJson("{\"value\":\"ONE\"}", TestData.class);
+    assertThat(data.value).isEqualTo(TestEnum.ONE);
+  }
+
+  @Test
+  public void mixedCaseEnumValueIsTreatedAsUnset() {
+    TestData data = gson.fromJson("{\"value\":\"oNe\"}", TestData.class);
+    assertThat(data.value).isNull();
+  }
+
+  @Test
+  public void lowerCaseEnumValueIsTreatedAsUnset() {
+    TestData data = gson.fromJson("{\"value\":\"one\"}", TestData.class);
+    assertThat(data.value).isNull();
+  }
+
+  @Test
+  public void notExistingEnumValueIsTreatedAsUnset() {
+    TestData data = gson.fromJson("{\"value\":\"FOUR\"}", TestData.class);
+    assertThat(data.value).isNull();
+  }
+
+  @Test
+  public void emptyEnumValueIsTreatedAsUnset() {
+    TestData data = gson.fromJson("{\"value\":\"\"}", TestData.class);
+    assertThat(data.value).isNull();
+  }
+
+  private static class TestData {
+    TestEnum value;
+
+    public TestData(TestEnum value) {
+      this.value = value;
+    }
+  }
+
+  private enum TestEnum {
+    ONE,
+    TWO
+  }
+}
diff --git a/javatests/com/google/gerrit/server/BUILD b/javatests/com/google/gerrit/server/BUILD
index 525a416..f6ed5ef 100644
--- a/javatests/com/google/gerrit/server/BUILD
+++ b/javatests/com/google/gerrit/server/BUILD
@@ -51,6 +51,7 @@
         "//java/com/google/gerrit/proto/testing",
         "//java/com/google/gerrit/reviewdb:server",
         "//java/com/google/gerrit/server",
+        "//java/com/google/gerrit/server/account/externalids/testing",
         "//java/com/google/gerrit/server/cache/serialize",
         "//java/com/google/gerrit/server/cache/testing",
         "//java/com/google/gerrit/server/group/testing",
@@ -75,6 +76,7 @@
         "//lib/guice",
         "//lib/jgit/org.eclipse.jgit:jgit",
         "//lib/jgit/org.eclipse.jgit.junit:junit",
+        "//lib/mockito",
         "//lib/truth",
         "//lib/truth:truth-java8-extension",
         "//lib/truth:truth-proto-extension",
diff --git a/javatests/com/google/gerrit/server/account/externalids/ExternalIDCacheLoaderTest.java b/javatests/com/google/gerrit/server/account/externalids/ExternalIDCacheLoaderTest.java
new file mode 100644
index 0000000..9cd8023
--- /dev/null
+++ b/javatests/com/google/gerrit/server/account/externalids/ExternalIDCacheLoaderTest.java
@@ -0,0 +1,307 @@
+// Copyright (C) 2019 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.account.externalids;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyZeroInteractions;
+import static org.mockito.Mockito.when;
+
+import com.google.common.cache.Cache;
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.metrics.DisabledMetricMaker;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.account.externalids.testing.ExternalIdTestUtil;
+import com.google.gerrit.server.config.AllUsersName;
+import com.google.gerrit.server.config.AllUsersNameProvider;
+import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.git.meta.MetaDataUpdate;
+import com.google.gerrit.testing.InMemoryRepositoryManager;
+import com.google.inject.util.Providers;
+import java.io.IOException;
+import java.util.function.Consumer;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.treewalk.TreeWalk;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.junit.MockitoJUnitRunner;
+
+@RunWith(MockitoJUnitRunner.class)
+public class ExternalIDCacheLoaderTest {
+  private static AllUsersName ALL_USERS = new AllUsersName(AllUsersNameProvider.DEFAULT);
+
+  @Mock Cache<ObjectId, AllExternalIds> externalIdCache;
+
+  private ExternalIdCacheLoader loader;
+  private GitRepositoryManager repoManager = new InMemoryRepositoryManager();
+  private ExternalIdReader externalIdReader;
+  private ExternalIdReader externalIdReaderSpy;
+
+  @Before
+  public void setUp() throws Exception {
+    repoManager.createRepository(ALL_USERS).close();
+    externalIdReader = new ExternalIdReader(repoManager, ALL_USERS, new DisabledMetricMaker());
+    externalIdReaderSpy = Mockito.spy(externalIdReader);
+    loader = createLoader(true);
+  }
+
+  @Test
+  public void worksOnSingleCommit() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    assertThat(loader.load(firstState)).isEqualTo(allFromGit(firstState));
+    verify(externalIdReaderSpy, times(1)).all(firstState);
+  }
+
+  @Test
+  public void reloadsSingleUpdateUsingPartialReload() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    ObjectId head = insertExternalId(2, 2);
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(allFromGit(firstState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void reloadsMultipleUpdatesUsingPartialReload() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    insertExternalId(2, 2);
+    insertExternalId(3, 3);
+    ObjectId head = insertExternalId(4, 4);
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(allFromGit(firstState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void reloadsAllExternalIdsWhenNoOldStateIsCached() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    ObjectId head = insertExternalId(2, 2);
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(null);
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verify(externalIdReaderSpy, times(1)).all(head);
+  }
+
+  @Test
+  public void partialReloadingDisabledAlwaysTriggersFullReload() throws Exception {
+    loader = createLoader(false);
+    insertExternalId(1, 1);
+    ObjectId head = insertExternalId(2, 2);
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verify(externalIdReaderSpy, times(1)).all(head);
+  }
+
+  @Test
+  public void fallsBackToFullReloadOnManyUpdatesOnBranch() throws Exception {
+    insertExternalId(1, 1);
+    ObjectId head = null;
+    for (int i = 2; i < 20; i++) {
+      head = insertExternalId(i, i);
+    }
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verify(externalIdReaderSpy, times(1)).all(head);
+  }
+
+  @Test
+  public void doesFullReloadWhenNoCacheStateIsFound() throws Exception {
+    ObjectId head = insertExternalId(1, 1);
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verify(externalIdReaderSpy, times(1)).all(head);
+  }
+
+  @Test
+  public void handlesDeletionInPartialReload() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    ObjectId head = deleteExternalId(1, 1);
+    assertThat(allFromGit(head).byAccount().size()).isEqualTo(0);
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(allFromGit(firstState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void handlesModifyInPartialReload() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    ObjectId head =
+        modifyExternalId(
+            externalId(1, 1),
+            ExternalId.create("fooschema", "bar1", Account.id(1), "foo@bar.com", "password"));
+    assertThat(allFromGit(head).byAccount().size()).isEqualTo(1);
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(allFromGit(firstState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void ignoresInvalidExternalId() throws Exception {
+    ObjectId firstState = insertExternalId(1, 1);
+    ObjectId head;
+    try (Repository repo = repoManager.openRepository(ALL_USERS);
+        RevWalk rw = new RevWalk(repo)) {
+      ExternalIdTestUtil.insertExternalIdWithKeyThatDoesntMatchNoteId(
+          repo, rw, new PersonIdent("foo", "foo@bar.com"), Account.id(2), "test");
+      head = repo.exactRef(RefNames.REFS_EXTERNAL_IDS).getObjectId();
+    }
+
+    when(externalIdCache.getIfPresent(firstState)).thenReturn(allFromGit(firstState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void handlesTreePrefixesInDifferentialReload() throws Exception {
+    // Create more than 256 notes (NoteMap's current sharding limit) and check that we really have
+    // created a situation where NoteNames are sharded.
+    ObjectId oldState = inserExternalIds(257);
+    assertAllFilesHaveSlashesInPath();
+    ObjectId head = insertExternalId(500, 500);
+
+    when(externalIdCache.getIfPresent(oldState)).thenReturn(allFromGit(oldState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  @Test
+  public void handlesReshard() throws Exception {
+    // Create 256 notes (NoteMap's current sharding limit) and check that we are not yet sharding
+    ObjectId oldState = inserExternalIds(256);
+    assertNoFilesHaveSlashesInPath();
+    // Create one more external ID and then have the Loader compute the new state
+    ObjectId head = insertExternalId(500, 500);
+    assertAllFilesHaveSlashesInPath(); // NoteMap resharded
+
+    when(externalIdCache.getIfPresent(oldState)).thenReturn(allFromGit(oldState));
+
+    assertThat(loader.load(head)).isEqualTo(allFromGit(head));
+    verifyZeroInteractions(externalIdReaderSpy);
+  }
+
+  private ExternalIdCacheLoader createLoader(boolean allowPartial) {
+    Config cfg = new Config();
+    cfg.setBoolean("cache", "external_ids_map", "enablePartialReloads", allowPartial);
+    return new ExternalIdCacheLoader(
+        repoManager,
+        ALL_USERS,
+        externalIdReaderSpy,
+        Providers.of(externalIdCache),
+        new DisabledMetricMaker(),
+        cfg);
+  }
+
+  private AllExternalIds allFromGit(ObjectId revision) throws Exception {
+    return AllExternalIds.create(externalIdReader.all(revision));
+  }
+
+  private ObjectId inserExternalIds(int numberOfIdsToInsert) throws Exception {
+    ObjectId oldState = null;
+    // Create more than 256 notes (NoteMap's current sharding limit) and check that we really have
+    // created a situation where NoteNames are sharded.
+    for (int i = 0; i < numberOfIdsToInsert; i++) {
+      oldState = insertExternalId(i, i);
+    }
+    return oldState;
+  }
+
+  private ObjectId insertExternalId(int key, int accountId) throws Exception {
+    return performExternalIdUpdate(
+        u -> {
+          try {
+            u.insert(externalId(key, accountId));
+          } catch (IOException e) {
+            throw new RuntimeException(e);
+          }
+        });
+  }
+
+  private ObjectId modifyExternalId(ExternalId oldId, ExternalId newId) throws Exception {
+    return performExternalIdUpdate(
+        u -> {
+          try {
+            u.replace(oldId, newId);
+          } catch (IOException e) {
+            throw new RuntimeException(e);
+          }
+        });
+  }
+
+  private ObjectId deleteExternalId(int key, int accountId) throws Exception {
+    return performExternalIdUpdate(u -> u.delete(externalId(key, accountId)));
+  }
+
+  private ExternalId externalId(int key, int accountId) {
+    return ExternalId.create("fooschema", "bar" + key, Account.id(accountId));
+  }
+
+  private ObjectId performExternalIdUpdate(Consumer<ExternalIdNotes> update) throws Exception {
+    try (Repository repo = repoManager.openRepository(ALL_USERS)) {
+      PersonIdent updater = new PersonIdent("Foo bar", "foo@bar.com");
+      ExternalIdNotes extIdNotes = ExternalIdNotes.loadNoCacheUpdate(ALL_USERS, repo);
+      update.accept(extIdNotes);
+      try (MetaDataUpdate metaDataUpdate =
+          new MetaDataUpdate(GitReferenceUpdated.DISABLED, null, repo)) {
+        metaDataUpdate.getCommitBuilder().setAuthor(updater);
+        metaDataUpdate.getCommitBuilder().setCommitter(updater);
+        return extIdNotes.commit(metaDataUpdate).getId();
+      }
+    }
+  }
+
+  private void assertAllFilesHaveSlashesInPath() throws Exception {
+    assertThat(allFilesInExternalIdRef().stream().allMatch(f -> f.contains("/"))).isTrue();
+  }
+
+  private void assertNoFilesHaveSlashesInPath() throws Exception {
+    assertThat(allFilesInExternalIdRef().stream().noneMatch(f -> f.contains("/"))).isTrue();
+  }
+
+  private ImmutableList<String> allFilesInExternalIdRef() throws Exception {
+    try (Repository repo = repoManager.openRepository(ALL_USERS);
+        TreeWalk treeWalk = new TreeWalk(repo);
+        RevWalk rw = new RevWalk(repo)) {
+      treeWalk.reset(
+          rw.parseCommit(repo.exactRef(RefNames.REFS_EXTERNAL_IDS).getObjectId()).getTree());
+      treeWalk.setRecursive(true);
+      ImmutableList.Builder<String> allPaths = ImmutableList.builder();
+      while (treeWalk.next()) {
+        allPaths.add(treeWalk.getPathString());
+      }
+      return allPaths.build();
+    }
+  }
+}
diff --git a/plugins/plugin-manager b/plugins/plugin-manager
index f681e7e..833889d 160000
--- a/plugins/plugin-manager
+++ b/plugins/plugin-manager
@@ -1 +1 @@
-Subproject commit f681e7ecb6ddbc52fe9e07cf3672ccdcad7d7d0b
+Subproject commit 833889d327a159b5ccea7064f4fcff3f94d4b26e
diff --git a/plugins/webhooks b/plugins/webhooks
index 8078749..f860a0c 160000
--- a/plugins/webhooks
+++ b/plugins/webhooks
@@ -1 +1 @@
-Subproject commit 8078749bfd64d9dcd3372bc3f8965d192747c5b4
+Subproject commit f860a0cf6931164a6e5c2b333eaa0004ea14acec
diff --git a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.js b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.js
index 4d7fd0c..5b728eb 100644
--- a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.js
+++ b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.js
@@ -198,10 +198,6 @@
       this.reload();
     },
 
-    _computeSelectedTitle(params) {
-      return this.getSelectedTitle(params.view);
-    },
-
     // TODO (beckysiegel): Update these functions after router abstraction is
     // updated. They are currently copied from gr-dropdown (and should be
     // updated there as well once complete).
@@ -228,6 +224,7 @@
      * @param {string=} opt_detailType
      */
     _computeSelectedClass(itemView, params, opt_detailType) {
+      if (!params) return '';
       // Group params are structured differently from admin params. Compute
       // selected differently for groups.
       // TODO(wyatta): Simplify this when all routes work like group params.
diff --git a/polygerrit-ui/app/elements/admin/gr-repo/gr-repo.js b/polygerrit-ui/app/elements/admin/gr-repo/gr-repo.js
index 08b59c2..fded936 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo/gr-repo.js
+++ b/polygerrit-ui/app/elements/admin/gr-repo/gr-repo.js
@@ -309,6 +309,9 @@
     },
 
     _computeCommands(repo, schemesObj, _selectedScheme) {
+      if (!schemesObj || !repo || !_selectedScheme) {
+        return [];
+      }
       const commands = [];
       let commandObj;
       if (schemesObj.hasOwnProperty(_selectedScheme)) {
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
index e69d48f..1e50e4b 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.html
@@ -176,7 +176,7 @@
           on-cancel="_handleConfirmDialogCancel"
           branch="[[change.branch]]"
           has-parent="[[hasParent]]"
-          rebase-on-current="[[revisionActions.rebase.rebaseOnCurrent]]"
+          rebase-on-current="[[_revisionRebaseAction.rebaseOnCurrent]]"
           hidden></gr-confirm-rebase-dialog>
       <gr-confirm-cherrypick-dialog id="confirmCherrypick"
           class="confirmDialog"
@@ -216,7 +216,7 @@
           id="confirmSubmitDialog"
           class="confirmDialog"
           change="[[change]]"
-          action="[[revisionActions.submit]]"
+          action="[[_revisionSubmitAction]]"
           on-cancel="_handleConfirmDialogCancel"
           on-confirm="_handleSubmitConfirm" hidden></gr-confirm-submit-dialog>
       <gr-dialog id="createFollowUpDialog"
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
index 83a454b..a448377 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.js
@@ -271,6 +271,20 @@
         type: Object,
         value() { return {}; },
       },
+      // If property binds directly to [[revisionActions.submit]] it is not
+      // updated when revisionActions doesn't contain submit action.
+      /** @type {?} */
+      _revisionSubmitAction: {
+        type: Object,
+        computed: '_getSubmitAction(revisionActions)',
+      },
+      // If property binds directly to [[revisionActions.rebase]] it is not
+      // updated when revisionActions doesn't contain rebase action.
+      /** @type {?} */
+      _revisionRebaseAction: {
+        type: Object,
+        computed: '_getRebaseAction(revisionActions)',
+      },
       privateByDefault: String,
 
       _loading: {
@@ -415,6 +429,28 @@
       this._handleLoadingComplete();
     },
 
+    _getSubmitAction(revisionActions) {
+      return this._getRevisionAction(revisionActions, 'submit', null);
+    },
+
+    _getRebaseAction(revisionActions) {
+      return this._getRevisionAction(revisionActions, 'rebase',
+        {rebaseOnCurrent: null}
+      );
+    },
+
+    _getRevisionAction(revisionActions, actionName, emptyActionValue) {
+      if (!revisionActions) {
+        return undefined;
+      }
+      if (revisionActions[actionName] === undefined) {
+        // Return null to fire an event when reveisionActions was loaded
+        // but doesn't contain actionName. undefined doesn't fire an event
+        return emptyActionValue;
+      }
+      return revisionActions[actionName];
+    },
+
     reload() {
       if (!this.changeNum || !this.latestPatchNum) {
         return Promise.resolve();
@@ -575,7 +611,9 @@
     _deleteAndNotify(actionName) {
       if (this.actions[actionName]) {
         delete this.actions[actionName];
-        this.notifyPath('actions.' + actionName);
+        // We assign a fake value of 'false' to support Polymer 2
+        // see https://github.com/Polymer/polymer/issues/2631
+        this.notifyPath('actions.' + actionName, false);
       }
     },
 
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
index 184e175..b88e06b 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_test.html
@@ -1513,4 +1513,50 @@
       assert.equal(reportStub.lastCall.args[0], 'type-key');
     });
   });
+
+  suite('getChangeRevisionActions returns only some actions', () => {
+    let element;
+    let sandbox;
+    let changeRevisionActions;
+
+    setup(() => {
+      stub('gr-rest-api-interface', {
+        getChangeRevisionActions() {
+          return Promise.resolve(changeRevisionActions);
+        },
+        send(method, url, payload) {
+          return Promise.reject(new Error('error'));
+        },
+        getProjectConfig() { return Promise.resolve({}); },
+      });
+
+      sandbox = sinon.sandbox.create();
+      sandbox.stub(Gerrit, 'awaitPluginsLoaded').returns(Promise.resolve());
+
+      element = fixture('basic');
+      // getChangeRevisionActions is not called without
+      // set the following properies
+      element.change = {};
+      element.changeNum = '42';
+      element.latestPatchNum = '2';
+
+
+      sandbox.stub(element.$.confirmCherrypick.$.restAPI,
+          'getRepoBranches').returns(Promise.resolve([]));
+      sandbox.stub(element.$.confirmMove.$.restAPI,
+          'getRepoBranches').returns(Promise.resolve([]));
+      return element.reload();
+    });
+
+    teardown(() => {
+      sandbox.restore();
+    });
+
+    test('confirmSubmitDialog and confirmRebase properties are changed', () => {
+      changeRevisionActions = {};
+      element.reload();
+      assert.strictEqual(element.$.confirmSubmitDialog.action, null);
+      assert.strictEqual(element.$.confirmRebase.rebaseOnCurrent, null);
+    });
+  });
 </script>
diff --git a/polygerrit-ui/app/elements/gr-app-element.html b/polygerrit-ui/app/elements/gr-app-element.html
index aff71f7..46c4502 100644
--- a/polygerrit-ui/app/elements/gr-app-element.html
+++ b/polygerrit-ui/app/elements/gr-app-element.html
@@ -196,7 +196,9 @@
       <div>
         <a class="feedback"
             href$="[[_feedbackUrl]]"
-            rel="noopener" target="_blank">Report bug</a>
+            rel="noopener"
+            target="_blank"
+            hidden$="[[!_showFeedbackUrl(_feedbackUrl)]]">Report bug</a>
         | Press &ldquo;?&rdquo; for keyboard shortcuts
         <gr-endpoint-decorator name="footer-right"></gr-endpoint-decorator>
       </div>
diff --git a/polygerrit-ui/app/elements/gr-app-element.js b/polygerrit-ui/app/elements/gr-app-element.js
index 4d556ae..eb35878 100644
--- a/polygerrit-ui/app/elements/gr-app-element.js
+++ b/polygerrit-ui/app/elements/gr-app-element.js
@@ -78,11 +78,7 @@
         computed: '_computePluginScreenName(params)',
       },
       _settingsUrl: String,
-      _feedbackUrl: {
-        type: String,
-        value: 'https://bugs.chromium.org/p/gerrit/issues/entry' +
-          '?template=PolyGerrit%20Issue',
-      },
+      _feedbackUrl: String,
       // Used to allow searching on mobile
       mobileSearch: {
         type: Boolean,
@@ -441,5 +437,13 @@
     _mobileSearchToggle(e) {
       this.mobileSearch = !this.mobileSearch;
     },
+
+    _showFeedbackUrl(feedbackUrl) {
+      if (feedbackUrl) {
+        return feedbackUrl;
+      }
+
+      return false;
+    },
   });
 })();
diff --git a/polygerrit-ui/app/elements/settings/gr-identities/gr-identities.html b/polygerrit-ui/app/elements/settings/gr-identities/gr-identities.html
index be851b1..a876611 100644
--- a/polygerrit-ui/app/elements/settings/gr-identities/gr-identities.html
+++ b/polygerrit-ui/app/elements/settings/gr-identities/gr-identities.html
@@ -27,8 +27,20 @@
   <template>
     <style include="shared-styles"></style>
     <style include="gr-form-styles">
-      td {
-        width: 5em;
+      tr th.emailAddressHeader,
+      tr th.identityHeader {
+        width: 15em;
+        padding: 0 10px;
+      }
+      tr td.statusColumn,
+      tr td.emailAddressColumn,
+      tr td.identityColumn {
+        word-break: break-word;
+      }
+      tr td.emailAddressColumn,
+      tr td.identityColumn {
+        padding: 4px 10px;
+        width: 15em;
       }
       .deleteButton {
         float: right;
@@ -36,40 +48,38 @@
       .deleteButton:not(.show) {
         display: none;
       }
-      .statusColumn {
-        white-space: nowrap;
-      }
     </style>
     <div class="gr-form-styles">
-      <table id="identities">
-        <thead>
-          <tr>
-            <th class="statusHeader">Status</th>
-            <th class="emailAddressHeader">Email Address</th>
-            <th class="identityHeader">Identity</th>
-            <th class="deleteHeader"></th>
-          </tr>
-        </thead>
-        <tbody>
-          <template is="dom-repeat" items="[[_identities]]" filter="filterIdentities">
+      <fieldset>
+        <table>
+          <thead>
             <tr>
-              <td class$="statusColumn">
-                [[_computeIsTrusted(item.trusted)]]
-              </td>
-              <td>[[item.email_address]]</td>
-              <td>[[_computeIdentity(item.identity)]]</td>
-              <td>
-                <gr-button
-                    link
-                    class$="deleteButton [[_computeHideDeleteClass(item.can_delete)]]"
-                    on-tap="_handleDeleteItem">
-                  Delete
-                </gr-button>
-              </td>
+              <th class="statusHeader">Status</th>
+              <th class="emailAddressHeader">Email Address</th>
+              <th class="identityHeader">Identity</th>
+              <th class="deleteHeader"></th>
             </tr>
-          </template>
-        </tbody>
-      </table>
+          </thead>
+          <tbody>
+            <template is="dom-repeat" items="[[_identities]]" filter="filterIdentities">
+              <tr>
+                <td class="statusColumn">
+                  [[_computeIsTrusted(item.trusted)]]
+                </td>
+                <td class="emailAddressColumn">[[item.email_address]]</td>
+                <td class="identityColumn">[[_computeIdentity(item.identity)]]</td>
+                <td class="deleteColumn">
+                  <gr-button
+                      class$="deleteButton [[_computeHideDeleteClass(item.can_delete)]]"
+                      on-tap="_handleDeleteItem">
+                    Delete
+                  </gr-button>
+                </td>
+              </tr>
+            </template>
+          </tbody>
+        </table>
+      </fieldset>
     </div>
     <gr-overlay id="overlay" with-backdrop>
       <gr-confirm-delete-item-dialog
diff --git a/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view.js b/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view.js
index 53d05e1..2508196 100644
--- a/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view.js
+++ b/polygerrit-ui/app/elements/shared/gr-list-view/gr-list-view.js
@@ -90,11 +90,11 @@
     },
 
     _hideNextArrow(loading, items) {
-      let lastPage = false;
-      if (items.length < this.itemsPerPage + 1) {
-        lastPage = true;
+      if (loading || !items || !items.length) {
+        return true;
       }
-      return loading || lastPage || !items || !items.length;
+      const lastPage = items.length < this.itemsPerPage + 1;
+      return lastPage;
     },
   });
 })();
diff --git a/polygerrit-ui/app/test/index.html b/polygerrit-ui/app/test/index.html
index 9448662..2b052a0 100644
--- a/polygerrit-ui/app/test/index.html
+++ b/polygerrit-ui/app/test/index.html
@@ -197,7 +197,6 @@
   for (let file of elements) {
     file = elementsPath + file;
     testFiles.push(file);
-    testFiles.push(file + '?dom=shadow');
   }
 
   // Behaviors tests.