diff --git a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
index 5fbd4118e5..dda8d14118 100644
--- a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
+++ b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/MigrateToNoteDb.java
@@ -20,8 +20,11 @@ import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toList;
 
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.gerrit.elasticsearch.ElasticIndexModule;
 import com.google.gerrit.extensions.config.FactoryModule;
 import com.google.gerrit.lifecycle.LifecycleManager;
+import com.google.gerrit.lucene.LuceneIndexModule;
 import com.google.gerrit.pgm.util.BatchProgramModule;
 import com.google.gerrit.pgm.util.RuntimeShutdown;
 import com.google.gerrit.pgm.util.SiteProgram;
@@ -30,10 +33,11 @@ import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.extensions.events.GitReferenceUpdated;
-import com.google.gerrit.server.index.DummyIndexModule;
+import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.notedb.rebuild.NoteDbMigrator;
 import com.google.inject.Inject;
 import com.google.inject.Injector;
+import com.google.inject.Module;
 import com.google.inject.Provider;
 import java.util.ArrayList;
 import java.util.List;
@@ -160,12 +164,23 @@ public class MigrateToNoteDb extends SiteProgram {
           public void configure() {
             install(dbInjector.getInstance(BatchProgramModule.class));
             bind(GitReferenceUpdated.class).toInstance(GitReferenceUpdated.DISABLED);
-            install(new DummyIndexModule());
+            install(getIndexModule());
             factory(ChangeResource.Factory.class);
           }
         });
   }
 
+  private Module getIndexModule() {
+    switch (IndexModule.getIndexType(dbInjector)) {
+      case LUCENE:
+        return LuceneIndexModule.singleVersionWithExplicitVersions(ImmutableMap.of(), threads);
+      case ELASTICSEARCH:
+        return ElasticIndexModule.singleVersionWithExplicitVersions(ImmutableMap.of(), threads);
+      default:
+        throw new IllegalStateException("unsupported index.type");
+    }
+  }
+
   private void stop() {
     try {
       LifecycleManager m = sysManager;
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/AccountCacheImpl.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/AccountCacheImpl.java
index 4c6f6703d3..44ffb90693 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/AccountCacheImpl.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/AccountCacheImpl.java
@@ -20,6 +20,7 @@ import static com.google.gerrit.server.account.externalids.ExternalId.SCHEME_USE
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Streams;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.common.TimeUtil;
 import com.google.gerrit.extensions.client.GeneralPreferencesInfo;
@@ -33,6 +34,7 @@ import com.google.gerrit.server.account.externalids.ExternalIds;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.config.AllUsersName;
 import com.google.gerrit.server.group.Groups;
+import com.google.gerrit.server.group.InternalGroup;
 import com.google.gerrit.server.index.account.AccountIndexer;
 import com.google.gerrit.server.query.account.InternalAccountQuery;
 import com.google.gwtorm.server.OrmException;
@@ -46,7 +48,6 @@ import com.google.inject.name.Named;
 import java.io.IOException;
 import java.util.Collections;
 import java.util.HashMap;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ExecutionException;
@@ -199,8 +200,8 @@ public class AccountCacheImpl implements AccountCache {
           groups
               .getGroupsWithMember(db, who)
               .map(groupCache::get)
-              .map(AccountGroup::getGroupUUID)
-              .filter(Objects::nonNull)
+              .flatMap(Streams::stream)
+              .map(InternalGroup::getGroupUUID)
               .collect(toImmutableSet());
 
       try {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCache.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCache.java
index 122c0bc836..82bcce377e 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCache.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCache.java
@@ -22,7 +22,14 @@ import java.util.Optional;
 
 /** Tracks group objects in memory for efficient access. */
 public interface GroupCache {
-  AccountGroup get(AccountGroup.Id groupId);
+  /**
+   * Looks up an internal group by its ID.
+   *
+   * @param groupId the ID of the internal group
+   * @return an {@code Optional} of the internal group, or an empty {@code Optional} if no internal
+   *     group with this ID exists on this server or an error occurred during lookup
+   */
+  Optional<InternalGroup> get(AccountGroup.Id groupId);
 
   /**
    * Looks up an internal group by its name.
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCacheImpl.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCacheImpl.java
index c95517b590..988439c8e7 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCacheImpl.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupCacheImpl.java
@@ -21,7 +21,6 @@ import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
-import com.google.gerrit.common.TimeUtil;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.server.ReviewDb;
@@ -57,7 +56,7 @@ public class GroupCacheImpl implements GroupCache {
     return new CacheModule() {
       @Override
       protected void configure() {
-        cache(BYID_NAME, AccountGroup.Id.class, new TypeLiteral<Optional<AccountGroup>>() {})
+        cache(BYID_NAME, AccountGroup.Id.class, new TypeLiteral<Optional<InternalGroup>>() {})
             .loader(ByIdLoader.class);
 
         cache(BYNAME_NAME, String.class, new TypeLiteral<Optional<InternalGroup>>() {})
@@ -72,7 +71,7 @@ public class GroupCacheImpl implements GroupCache {
     };
   }
 
-  private final LoadingCache<AccountGroup.Id, Optional<AccountGroup>> byId;
+  private final LoadingCache<AccountGroup.Id, Optional<InternalGroup>> byId;
   private final LoadingCache<String, Optional<InternalGroup>> byName;
   private final LoadingCache<String, Optional<InternalGroup>> byUUID;
   private final SchemaFactory<ReviewDb> schema;
@@ -81,7 +80,7 @@ public class GroupCacheImpl implements GroupCache {
 
   @Inject
   GroupCacheImpl(
-      @Named(BYID_NAME) LoadingCache<AccountGroup.Id, Optional<AccountGroup>> byId,
+      @Named(BYID_NAME) LoadingCache<AccountGroup.Id, Optional<InternalGroup>> byId,
       @Named(BYNAME_NAME) LoadingCache<String, Optional<InternalGroup>> byName,
       @Named(BYUUID_NAME) LoadingCache<String, Optional<InternalGroup>> byUUID,
       SchemaFactory<ReviewDb> schema,
@@ -96,13 +95,12 @@ public class GroupCacheImpl implements GroupCache {
   }
 
   @Override
-  public AccountGroup get(AccountGroup.Id groupId) {
+  public Optional<InternalGroup> get(AccountGroup.Id groupId) {
     try {
-      Optional<AccountGroup> g = byId.get(groupId);
-      return g.isPresent() ? g.get() : missing(groupId);
+      return byId.get(groupId);
     } catch (ExecutionException e) {
       log.warn("Cannot load group " + groupId, e);
-      return missing(groupId);
+      return Optional.empty();
     }
   }
 
@@ -171,26 +169,17 @@ public class GroupCacheImpl implements GroupCache {
     indexer.get().index(group.getGroupUUID());
   }
 
-  private static AccountGroup missing(AccountGroup.Id key) {
-    AccountGroup.NameKey name = new AccountGroup.NameKey("Deleted Group" + key);
-    return new AccountGroup(name, key, null, TimeUtil.nowTs());
-  }
-
-  static class ByIdLoader extends CacheLoader<AccountGroup.Id, Optional<AccountGroup>> {
-    private final SchemaFactory<ReviewDb> schema;
-    private final Groups groups;
+  static class ByIdLoader extends CacheLoader<AccountGroup.Id, Optional<InternalGroup>> {
+    private final Provider<InternalGroupQuery> groupQueryProvider;
 
     @Inject
-    ByIdLoader(SchemaFactory<ReviewDb> sf, Groups groups) {
-      schema = sf;
-      this.groups = groups;
+    ByIdLoader(Provider<InternalGroupQuery> groupQueryProvider) {
+      this.groupQueryProvider = groupQueryProvider;
     }
 
     @Override
-    public Optional<AccountGroup> load(AccountGroup.Id key) throws Exception {
-      try (ReviewDb db = schema.open()) {
-        return groups.getGroup(db, key);
-      }
+    public Optional<InternalGroup> load(AccountGroup.Id key) throws Exception {
+      return groupQueryProvider.get().byId(key);
     }
   }
 
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupControl.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupControl.java
index 5af4898a8c..020a04dc88 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupControl.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupControl.java
@@ -21,12 +21,15 @@ import com.google.gerrit.extensions.restapi.AuthException;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.group.InternalGroup;
+import com.google.gerrit.server.group.InternalGroupDescription;
 import com.google.gerrit.server.permissions.GlobalPermission;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.google.inject.Singleton;
+import java.util.Optional;
 
 /** Access control management for a group of accounts managed in Gerrit. */
 public class GroupControl {
@@ -71,11 +74,11 @@ public class GroupControl {
     }
 
     public GroupControl controlFor(AccountGroup.Id groupId) throws NoSuchGroupException {
-      final AccountGroup group = groupCache.get(groupId);
-      if (group == null) {
-        throw new NoSuchGroupException(groupId);
-      }
-      return controlFor(GroupDescriptions.forAccountGroup(group));
+      Optional<InternalGroup> group = groupCache.get(groupId);
+      return group
+          .map(InternalGroupDescription::new)
+          .map(this::controlFor)
+          .orElseThrow(() -> new NoSuchGroupException(groupId));
     }
 
     public GroupControl controlFor(AccountGroup.UUID groupId) throws NoSuchGroupException {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupIncludeCacheImpl.java b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupIncludeCacheImpl.java
index 10c002c01f..c686928c96 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupIncludeCacheImpl.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/account/GroupIncludeCacheImpl.java
@@ -19,11 +19,13 @@ import static com.google.common.collect.ImmutableList.toImmutableList;
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
 import com.google.gerrit.common.errors.NoSuchGroupException;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.group.Groups;
+import com.google.gerrit.server.group.InternalGroup;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
@@ -33,7 +35,6 @@ import com.google.inject.TypeLiteral;
 import com.google.inject.name.Named;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.Objects;
 import java.util.concurrent.ExecutionException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -174,8 +175,8 @@ public class GroupIncludeCacheImpl implements GroupIncludeCache {
         return groups
             .getParentGroups(db, key)
             .map(groupCache::get)
-            .map(AccountGroup::getGroupUUID)
-            .filter(Objects::nonNull)
+            .flatMap(Streams::stream)
+            .map(InternalGroup::getGroupUUID)
             .collect(toImmutableList());
       }
     }
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/group/CreateGroup.java b/gerrit-server/src/main/java/com/google/gerrit/server/group/CreateGroup.java
index a1aefc5147..e55397ec64 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/group/CreateGroup.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/group/CreateGroup.java
@@ -56,6 +56,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
+import java.util.Optional;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.PersonIdent;
@@ -198,10 +199,8 @@ public class CreateGroup implements RestModifyView<TopLevelResource, GroupInput>
         new AccountGroup(createGroupArgs.getGroup(), groupId, uuid, TimeUtil.nowTs());
     group.setVisibleToAll(createGroupArgs.visibleToAll);
     if (createGroupArgs.ownerGroupId != null) {
-      AccountGroup ownerGroup = groupCache.get(createGroupArgs.ownerGroupId);
-      if (ownerGroup != null) {
-        group.setOwnerGroupUUID(ownerGroup.getGroupUUID());
-      }
+      Optional<InternalGroup> ownerGroup = groupCache.get(createGroupArgs.ownerGroupId);
+      ownerGroup.map(InternalGroup::getGroupUUID).ifPresent(group::setOwnerGroupUUID);
     }
     if (createGroupArgs.groupDescription != null) {
       group.setDescription(createGroupArgs.groupDescription);
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/group/DbGroupMemberAuditListener.java b/gerrit-server/src/main/java/com/google/gerrit/server/group/DbGroupMemberAuditListener.java
index ce287d0c0d..5af7ebdf8b 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/group/DbGroupMemberAuditListener.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/group/DbGroupMemberAuditListener.java
@@ -152,7 +152,7 @@ class DbGroupMemberAuditListener implements GroupMemberAuditListener {
       Account.Id accountId = m.getAccountId();
       String userName = accountCache.get(accountId).getUserName();
       AccountGroup.Id groupId = m.getAccountGroupId();
-      String groupName = groupCache.get(groupId).getName();
+      String groupName = getGroupName(groupId);
 
       descriptions.add(
           MessageFormat.format(
@@ -168,7 +168,7 @@ class DbGroupMemberAuditListener implements GroupMemberAuditListener {
       AccountGroup.UUID groupUuid = m.getIncludeUUID();
       String groupName = groupBackend.get(groupUuid).getName();
       AccountGroup.Id targetGroupId = m.getGroupId();
-      String targetGroupName = groupCache.get(targetGroupId).getName();
+      String targetGroupName = getGroupName(targetGroupId);
 
       descriptions.add(
           MessageFormat.format(
@@ -178,6 +178,10 @@ class DbGroupMemberAuditListener implements GroupMemberAuditListener {
     logOrmException(header, me, descriptions, e);
   }
 
+  private String getGroupName(AccountGroup.Id groupId) {
+    return groupCache.get(groupId).map(InternalGroup::getName).orElse("Deleted group " + groupId);
+  }
+
   private void logOrmException(String header, Account.Id me, Iterable<?> values, OrmException e) {
     StringBuilder message = new StringBuilder(header);
     message.append(" ");
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/group/Groups.java b/gerrit-server/src/main/java/com/google/gerrit/server/group/Groups.java
index a1947ecfca..1e5d634445 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/group/Groups.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/group/Groups.java
@@ -59,18 +59,6 @@ public class Groups {
     return group.orElseThrow(() -> new NoSuchGroupException(groupUuid));
   }
 
-  /**
-   * Returns the {@code AccountGroup} for the specified ID if it exists.
-   *
-   * @param db the {@code ReviewDb} instance to use for lookups
-   * @param groupId the ID of the group
-   * @return the found {@code AccountGroup} if it exists, or else an empty {@code Optional}
-   * @throws OrmException if the group couldn't be retrieved from ReviewDb
-   */
-  public Optional<AccountGroup> getGroup(ReviewDb db, AccountGroup.Id groupId) throws OrmException {
-    return Optional.ofNullable(db.accountGroups().get(groupId));
-  }
-
   /**
    * Returns the {@code AccountGroup} for the specified UUID if it exists.
    *
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/query/group/GroupPredicates.java b/gerrit-server/src/main/java/com/google/gerrit/server/query/group/GroupPredicates.java
index 983d3b3694..d02f6a46fa 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/query/group/GroupPredicates.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/query/group/GroupPredicates.java
@@ -24,6 +24,10 @@ import com.google.gerrit.server.index.group.GroupField;
 import java.util.Locale;
 
 public class GroupPredicates {
+  public static Predicate<InternalGroup> id(AccountGroup.Id groupId) {
+    return new GroupPredicate(GroupField.ID, groupId.toString());
+  }
+
   public static Predicate<InternalGroup> uuid(AccountGroup.UUID uuid) {
     return new GroupPredicate(GroupField.UUID, GroupQueryBuilder.FIELD_UUID, uuid.get());
   }
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/query/group/InternalGroupQuery.java b/gerrit-server/src/main/java/com/google/gerrit/server/query/group/InternalGroupQuery.java
index b261e259fe..513fffe78a 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/query/group/InternalGroupQuery.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/query/group/InternalGroupQuery.java
@@ -20,6 +20,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.gerrit.index.IndexConfig;
 import com.google.gerrit.index.query.InternalQuery;
+import com.google.gerrit.index.query.Predicate;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.server.group.InternalGroup;
 import com.google.gerrit.server.index.group.GroupIndexCollection;
@@ -46,7 +47,16 @@ public class InternalGroupQuery extends InternalQuery<InternalGroup> {
   }
 
   public Optional<InternalGroup> byName(AccountGroup.NameKey groupName) throws OrmException {
-    List<InternalGroup> groups = query(GroupPredicates.name(groupName.get()));
+    return getOnlyGroup(GroupPredicates.name(groupName.get()), "group name '" + groupName + "'");
+  }
+
+  public Optional<InternalGroup> byId(AccountGroup.Id groupId) throws OrmException {
+    return getOnlyGroup(GroupPredicates.id(groupId), "group id '" + groupId + "'");
+  }
+
+  private Optional<InternalGroup> getOnlyGroup(
+      Predicate<InternalGroup> predicate, String groupDescription) throws OrmException {
+    List<InternalGroup> groups = query(predicate);
     if (groups.isEmpty()) {
       return Optional.empty();
     }
@@ -57,7 +67,7 @@ public class InternalGroupQuery extends InternalQuery<InternalGroup> {
 
     ImmutableList<AccountGroup.UUID> groupUuids =
         groups.stream().map(InternalGroup::getGroupUUID).collect(toImmutableList());
-    log.warn(String.format("Ambiguous group name '%s' for groups %s.", groupName, groupUuids));
+    log.warn(String.format("Ambiguous %s for groups %s.", groupDescription, groupUuids));
     return Optional.empty();
   }
 }