diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 750a002..95078c1 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -3054,7 +3054,7 @@
 [[index.batchThreads]]index.batchThreads::
 +
 Number of threads to use for indexing in background operations, such as
-online schema upgrades, and also for offline reindexing.
+online schema upgrades, and also the default for offline reindexing.
 +
 If not set or set to a zero, defaults to the number of logical CPUs as returned
 by the JVM. If set to a negative value, defaults to a direct executor.
@@ -3257,6 +3257,11 @@
 +
 Defaults to true (throttling enabled).
 
+During offline reindexing, setting ramBufferSize greater than the size
+of index (size of specific index folder under <site_dir>/index) and
+maxBufferedDocs as -1 avoids unnecessary flushes and triggers only a
+single flush at the end of the process.
+
 Sample Lucene index configuration:
 ----
 [index]
diff --git a/Documentation/pgm-reindex.txt b/Documentation/pgm-reindex.txt
index 5167277..5392564 100644
--- a/Documentation/pgm-reindex.txt
+++ b/Documentation/pgm-reindex.txt
@@ -20,7 +20,8 @@
 
 == OPTIONS
 --threads::
-	Number of threads to use for indexing.
+	Number of threads to use for indexing. Default is
+	link:config-gerrit.html#index.batchThreads[index.batchThreads]
 
 --changes-schema-version::
 	Schema version to reindex; default is most recent version.
diff --git a/java/com/google/gerrit/acceptance/GerritServer.java b/java/com/google/gerrit/acceptance/GerritServer.java
index 3f8a5a8..cfc0ce4 100644
--- a/java/com/google/gerrit/acceptance/GerritServer.java
+++ b/java/com/google/gerrit/acceptance/GerritServer.java
@@ -51,6 +51,7 @@
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePath;
 import com.google.gerrit.server.git.receive.AsyncReceiveCommits;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.schema.JdbcAccountPatchReviewStore;
 import com.google.gerrit.server.ssh.NoSshModule;
 import com.google.gerrit.server.util.ReplicaUtil;
@@ -428,7 +429,8 @@
         "accountPatchReviewDb", null, "url", JdbcAccountPatchReviewStore.TEST_IN_MEMORY_URL);
     daemon.setEnableHttpd(desc.httpd());
     daemon.setLuceneModule(
-        LuceneIndexModule.singleVersionAllLatest(0, ReplicaUtil.isReplica(baseConfig)));
+        LuceneIndexModule.singleVersionAllLatest(
+            0, ReplicaUtil.isReplica(baseConfig), AutoFlush.ENABLED));
     daemon.setDatabaseForTesting(
         ImmutableList.of(
             new InMemoryTestingDatabaseModule(cfg, site, inMemoryRepoManager),
diff --git a/java/com/google/gerrit/httpd/init/WebAppInitializer.java b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
index 193c4f1..e4a86f5 100644
--- a/java/com/google/gerrit/httpd/init/WebAppInitializer.java
+++ b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
@@ -79,6 +79,7 @@
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.OnlineUpgrader;
 import com.google.gerrit.server.index.VersionManager;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.mail.SignedTokenEmailTokenVerifier;
 import com.google.gerrit.server.mail.receive.MailReceiver;
 import com.google.gerrit.server.mail.send.SmtpEmailSender;
@@ -357,7 +358,7 @@
 
   private Module createIndexModule() {
     if (indexType.isLucene()) {
-      return LuceneIndexModule.latestVersion(false);
+      return LuceneIndexModule.latestVersion(false, AutoFlush.ENABLED);
     } else if (indexType.isElasticsearch()) {
       return ElasticIndexModule.latestVersion(false);
     } else {
diff --git a/java/com/google/gerrit/lucene/AbstractLuceneIndex.java b/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
index 5392ab4..1e6ccac 100644
--- a/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
+++ b/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
@@ -45,6 +45,7 @@
 import com.google.gerrit.index.query.ResultSet;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.IndexUtils;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.logging.LoggingContextAwareExecutorService;
 import com.google.gerrit.server.logging.LoggingContextAwareScheduledExecutorService;
 import java.io.IOException;
@@ -105,6 +106,7 @@
   private final ReferenceManager<IndexSearcher> searcherManager;
   private final ControlledRealTimeReopenThread<IndexSearcher> reopenThread;
   private final Set<NrtFuture> notDoneNrtFutures;
+  private final AutoFlush autoFlush;
   private ScheduledExecutorService autoCommitExecutor;
 
   AbstractLuceneIndex(
@@ -115,13 +117,15 @@
       ImmutableSet<String> skipFields,
       String subIndex,
       GerritIndexWriterConfig writerConfig,
-      SearcherFactory searcherFactory)
+      SearcherFactory searcherFactory,
+      AutoFlush autoFlush)
       throws IOException {
     this.schema = schema;
     this.sitePaths = sitePaths;
     this.dir = dir;
     this.name = name;
     this.skipFields = skipFields;
+    this.autoFlush = autoFlush;
     String index = Joiner.on('_').skipNulls().join(name, subIndex);
     long commitPeriod = writerConfig.getCommitWithinMs();
 
@@ -215,7 +219,9 @@
           }
         });
 
-    reopenThread.start();
+    if (autoFlush.equals(AutoFlush.ENABLED)) {
+      reopenThread.start();
+    }
   }
 
   @Override
@@ -484,6 +490,9 @@
     }
 
     private boolean isGenAvailableNowForCurrentSearcher() {
+      if (autoFlush.equals(AutoFlush.DISABLED)) {
+        return true;
+      }
       try {
         return reopenThread.waitForGeneration(gen, 0);
       } catch (InterruptedException e) {
diff --git a/java/com/google/gerrit/lucene/ChangeSubIndex.java b/java/com/google/gerrit/lucene/ChangeSubIndex.java
index e51a91a7..5c24b9a 100644
--- a/java/com/google/gerrit/lucene/ChangeSubIndex.java
+++ b/java/com/google/gerrit/lucene/ChangeSubIndex.java
@@ -33,6 +33,7 @@
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.change.ChangeField;
 import com.google.gerrit.server.index.change.ChangeIndex;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.query.change.ChangeData;
 import java.io.IOException;
 import java.nio.file.Path;
@@ -51,7 +52,8 @@
       Path path,
       ImmutableSet<String> skipFields,
       GerritIndexWriterConfig writerConfig,
-      SearcherFactory searcherFactory)
+      SearcherFactory searcherFactory,
+      AutoFlush autoFlush)
       throws IOException {
     this(
         schema,
@@ -60,7 +62,8 @@
         path.getFileName().toString(),
         skipFields,
         writerConfig,
-        searcherFactory);
+        searcherFactory,
+        autoFlush);
   }
 
   ChangeSubIndex(
@@ -70,9 +73,19 @@
       String subIndex,
       ImmutableSet<String> skipFields,
       GerritIndexWriterConfig writerConfig,
-      SearcherFactory searcherFactory)
+      SearcherFactory searcherFactory,
+      AutoFlush autoFlush)
       throws IOException {
-    super(schema, sitePaths, dir, NAME, skipFields, subIndex, writerConfig, searcherFactory);
+    super(
+        schema,
+        sitePaths,
+        dir,
+        NAME,
+        skipFields,
+        subIndex,
+        writerConfig,
+        searcherFactory,
+        autoFlush);
   }
 
   @Override
diff --git a/java/com/google/gerrit/lucene/LuceneAccountIndex.java b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
index 242cffd..87b7cce 100644
--- a/java/com/google/gerrit/lucene/LuceneAccountIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
@@ -36,6 +36,7 @@
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.index.account.AccountIndex;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.google.inject.assistedinject.Assisted;
@@ -94,7 +95,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<AccountCache> accountCache,
-      @Assisted Schema<AccountState> schema)
+      @Assisted Schema<AccountState> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -104,7 +106,8 @@
         ImmutableSet.of(),
         null,
         new GerritIndexWriterConfig(cfg, ACCOUNTS),
-        new SearcherFactory());
+        new SearcherFactory(),
+        autoFlush);
     this.accountCache = accountCache;
 
     indexWriterConfig = new GerritIndexWriterConfig(cfg, ACCOUNTS);
diff --git a/java/com/google/gerrit/lucene/LuceneChangeIndex.java b/java/com/google/gerrit/lucene/LuceneChangeIndex.java
index bf1a166..bb97936b 100644
--- a/java/com/google/gerrit/lucene/LuceneChangeIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneChangeIndex.java
@@ -64,6 +64,7 @@
 import com.google.gerrit.server.index.change.ChangeField;
 import com.google.gerrit.server.index.change.ChangeIndex;
 import com.google.gerrit.server.index.change.ChangeIndexRewriter;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.project.SubmitRuleOptions;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.query.change.ChangeDataSource;
@@ -179,7 +180,8 @@
       SitePaths sitePaths,
       @IndexExecutor(INTERACTIVE) ListeningExecutorService executor,
       ChangeData.Factory changeDataFactory,
-      @Assisted Schema<ChangeData> schema)
+      @Assisted Schema<ChangeData> schema,
+      AutoFlush autoFlush)
       throws IOException {
     this.executor = executor;
     this.changeDataFactory = changeDataFactory;
@@ -204,7 +206,8 @@
               "ramOpen",
               skipFields,
               openConfig,
-              searcherFactory);
+              searcherFactory,
+              autoFlush);
       closedIndex =
           new ChangeSubIndex(
               schema,
@@ -213,7 +216,8 @@
               "ramClosed",
               skipFields,
               closedConfig,
-              searcherFactory);
+              searcherFactory,
+              autoFlush);
     } else {
       Path dir = LuceneVersionManager.getDir(sitePaths, CHANGES, schema);
       openIndex =
@@ -223,7 +227,8 @@
               dir.resolve(CHANGES_OPEN),
               skipFields,
               openConfig,
-              searcherFactory);
+              searcherFactory,
+              autoFlush);
       closedIndex =
           new ChangeSubIndex(
               schema,
@@ -231,7 +236,8 @@
               dir.resolve(CHANGES_CLOSED),
               skipFields,
               closedConfig,
-              searcherFactory);
+              searcherFactory,
+              autoFlush);
     }
 
     idField = this.schema.useLegacyNumericFields() ? LEGACY_ID : LEGACY_ID_STR;
diff --git a/java/com/google/gerrit/lucene/LuceneGroupIndex.java b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
index 3d1d471..c1b44c7 100644
--- a/java/com/google/gerrit/lucene/LuceneGroupIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
@@ -33,6 +33,7 @@
 import com.google.gerrit.server.group.InternalGroup;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.index.group.GroupIndex;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.google.inject.assistedinject.Assisted;
@@ -84,7 +85,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<GroupCache> groupCache,
-      @Assisted Schema<InternalGroup> schema)
+      @Assisted Schema<InternalGroup> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -94,7 +96,8 @@
         ImmutableSet.of(),
         null,
         new GerritIndexWriterConfig(cfg, GROUPS),
-        new SearcherFactory());
+        new SearcherFactory(),
+        autoFlush);
     this.groupCache = groupCache;
 
     indexWriterConfig = new GerritIndexWriterConfig(cfg, GROUPS);
diff --git a/java/com/google/gerrit/lucene/LuceneIndexModule.java b/java/com/google/gerrit/lucene/LuceneIndexModule.java
index 302a2da..73256b1 100644
--- a/java/com/google/gerrit/lucene/LuceneIndexModule.java
+++ b/java/com/google/gerrit/lucene/LuceneIndexModule.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.lucene;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.index.IndexConfig;
 import com.google.gerrit.index.project.ProjectIndex;
@@ -23,30 +24,48 @@
 import com.google.gerrit.server.index.account.AccountIndex;
 import com.google.gerrit.server.index.change.ChangeIndex;
 import com.google.gerrit.server.index.group.GroupIndex;
+import com.google.gerrit.server.index.options.AutoFlush;
 import java.util.Map;
 import org.apache.lucene.search.BooleanQuery;
 import org.eclipse.jgit.lib.Config;
 
 public class LuceneIndexModule extends AbstractIndexModule {
-  public static LuceneIndexModule singleVersionAllLatest(int threads, boolean slave) {
-    return new LuceneIndexModule(ImmutableMap.of(), threads, slave);
+  private final AutoFlush autoFlush;
+
+  public static LuceneIndexModule singleVersionAllLatest(
+      int threads, boolean slave, AutoFlush autoFlush) {
+    return new LuceneIndexModule(ImmutableMap.of(), threads, slave, autoFlush);
+  }
+
+  @VisibleForTesting
+  public static LuceneIndexModule singleVersionWithExplicitVersions(
+      Map<String, Integer> versions, int threads, boolean slave) {
+    return new LuceneIndexModule(versions, threads, slave, AutoFlush.ENABLED);
   }
 
   public static LuceneIndexModule singleVersionWithExplicitVersions(
-      Map<String, Integer> versions, int threads, boolean slave) {
-    return new LuceneIndexModule(versions, threads, slave);
+      Map<String, Integer> versions, int threads, boolean slave, AutoFlush autoFlush) {
+    return new LuceneIndexModule(versions, threads, slave, autoFlush);
   }
 
-  public static LuceneIndexModule latestVersion(boolean slave) {
-    return new LuceneIndexModule(null, 0, slave);
+  public static LuceneIndexModule latestVersion(boolean slave, AutoFlush autoFlush) {
+    return new LuceneIndexModule(null, 0, slave, autoFlush);
   }
 
   static boolean isInMemoryTest(Config cfg) {
     return cfg.getBoolean("index", "lucene", "testInmemory", false);
   }
 
-  private LuceneIndexModule(Map<String, Integer> singleVersions, int threads, boolean slave) {
+  private LuceneIndexModule(
+      Map<String, Integer> singleVersions, int threads, boolean slave, AutoFlush autoFlush) {
     super(singleVersions, threads, slave);
+    this.autoFlush = autoFlush;
+  }
+
+  @Override
+  protected void configure() {
+    super.configure();
+    bind(AutoFlush.class).toInstance(autoFlush);
   }
 
   @Override
diff --git a/java/com/google/gerrit/lucene/LuceneProjectIndex.java b/java/com/google/gerrit/lucene/LuceneProjectIndex.java
index 2a418ca..7e7aecb 100644
--- a/java/com/google/gerrit/lucene/LuceneProjectIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneProjectIndex.java
@@ -32,6 +32,7 @@
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.IndexUtils;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.inject.Inject;
@@ -84,7 +85,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<ProjectCache> projectCache,
-      @Assisted Schema<ProjectData> schema)
+      @Assisted Schema<ProjectData> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -94,7 +96,8 @@
         ImmutableSet.of(),
         null,
         new GerritIndexWriterConfig(cfg, PROJECTS),
-        new SearcherFactory());
+        new SearcherFactory(),
+        autoFlush);
     this.projectCache = projectCache;
 
     indexWriterConfig = new GerritIndexWriterConfig(cfg, PROJECTS);
diff --git a/java/com/google/gerrit/pgm/Daemon.java b/java/com/google/gerrit/pgm/Daemon.java
index f21a350..5f675bcc 100644
--- a/java/com/google/gerrit/pgm/Daemon.java
+++ b/java/com/google/gerrit/pgm/Daemon.java
@@ -87,6 +87,7 @@
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.OnlineUpgrader;
 import com.google.gerrit.server.index.VersionManager;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.mail.SignedTokenEmailTokenVerifier;
 import com.google.gerrit.server.mail.receive.MailReceiver;
 import com.google.gerrit.server.mail.send.SmtpEmailSender;
@@ -518,7 +519,7 @@
       return luceneModule;
     }
     if (indexType.isLucene()) {
-      return LuceneIndexModule.latestVersion(replica);
+      return LuceneIndexModule.latestVersion(replica, AutoFlush.ENABLED);
     }
     if (indexType.isElasticsearch()) {
       return ElasticIndexModule.latestVersion(replica);
diff --git a/java/com/google/gerrit/pgm/Reindex.java b/java/com/google/gerrit/pgm/Reindex.java
index 3935268..0872340 100644
--- a/java/com/google/gerrit/pgm/Reindex.java
+++ b/java/com/google/gerrit/pgm/Reindex.java
@@ -33,6 +33,7 @@
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.change.ChangeSchemaDefinitions;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.gerrit.server.plugins.PluginGuiceEnvironment;
 import com.google.gerrit.server.util.ReplicaUtil;
 import com.google.inject.Inject;
@@ -52,8 +53,10 @@
 import org.kohsuke.args4j.Option;
 
 public class Reindex extends SiteProgram {
-  @Option(name = "--threads", usage = "Number of threads to use for indexing")
-  private int threads = Runtime.getRuntime().availableProcessors();
+  @Option(
+      name = "--threads",
+      usage = "Number of threads to use for indexing. Default is index.batchThreads from config.")
+  private int threads = 0;
 
   @Option(
       name = "--changes-schema-version",
@@ -150,7 +153,9 @@
     Module indexModule;
     IndexType indexType = IndexModule.getIndexType(dbInjector);
     if (indexType.isLucene()) {
-      indexModule = LuceneIndexModule.singleVersionWithExplicitVersions(versions, threads, replica);
+      indexModule =
+          LuceneIndexModule.singleVersionWithExplicitVersions(
+              versions, threads, replica, AutoFlush.DISABLED);
     } else if (indexType.isElasticsearch()) {
       indexModule =
           ElasticIndexModule.singleVersionWithExplicitVersions(versions, threads, replica);
diff --git a/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java b/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java
index 12a44dc..078e648 100644
--- a/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java
+++ b/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java
@@ -19,6 +19,7 @@
 import com.google.gerrit.pgm.init.index.IndexModuleOnInit;
 import com.google.gerrit.server.index.account.AccountIndex;
 import com.google.gerrit.server.index.group.GroupIndex;
+import com.google.gerrit.server.index.options.AutoFlush;
 import com.google.inject.AbstractModule;
 import com.google.inject.assistedinject.FactoryModuleBuilder;
 
@@ -36,5 +37,7 @@
             .build(GroupIndex.Factory.class));
 
     install(new IndexModuleOnInit());
+
+    bind(AutoFlush.class).toInstance(AutoFlush.DISABLED);
   }
 }
diff --git a/java/com/google/gerrit/server/git/meta/VersionedMetaData.java b/java/com/google/gerrit/server/git/meta/VersionedMetaData.java
index feb038a..ea594dd 100644
--- a/java/com/google/gerrit/server/git/meta/VersionedMetaData.java
+++ b/java/com/google/gerrit/server/git/meta/VersionedMetaData.java
@@ -217,6 +217,27 @@
   }
 
   /**
+   * Update this metadata branch, recording a new commit on its reference. This method mutates its
+   * receiver.
+   *
+   * @param update helper information to define the update that will occur.
+   * @param objInserter Shared object inserter.
+   * @param objReader Shared object reader.
+   * @param revWalk Shared rev walk.
+   * @return the commit that was created
+   * @throws IOException if there is a storage problem and the update cannot be executed as
+   *     requested or if it failed because of a concurrent update to the same reference
+   */
+  public RevCommit commit(
+      MetaDataUpdate update, ObjectInserter objInserter, ObjectReader objReader, RevWalk revWalk)
+      throws IOException {
+    try (BatchMetaDataUpdate batch = openUpdate(update, objInserter, objReader, revWalk)) {
+      batch.write(update.getCommitBuilder());
+      return batch.commit();
+    }
+  }
+
+  /**
    * Creates a new commit and a new ref based on this commit. This method mutates its receiver.
    *
    * @param update helper information to define the update that will occur.
@@ -263,11 +284,39 @@
    * @throws IOException if the update failed.
    */
   public BatchMetaDataUpdate openUpdate(MetaDataUpdate update) throws IOException {
+    return openUpdate(update, null, null, null);
+  }
+
+  /**
+   * Open a batch of updates to the same metadata ref.
+   *
+   * <p>This allows making multiple commits to a single metadata ref, at the end of which is a
+   * single ref update. For batching together updates to multiple refs (each consisting of one or
+   * more commits against their respective refs), create the {@link MetaDataUpdate} with a {@link
+   * BatchRefUpdate}.
+   *
+   * <p>A ref update produced by this {@link BatchMetaDataUpdate} is only committed if there is no
+   * associated {@link BatchRefUpdate}. As a result, the configured ref updated event is not fired
+   * if there is an associated batch.
+   *
+   * <p>If object inserter, reader and revwalk are provided, then the updates are not flushed,
+   * allowing callers the flexibility to flush only once after several updates.
+   *
+   * @param update helper info about the update.
+   * @param objInserter Shared object inserter.
+   * @param objReader Shared object reader.
+   * @param revWalk Shared rev walk.
+   * @throws IOException if the update failed.
+   */
+  public BatchMetaDataUpdate openUpdate(
+      MetaDataUpdate update, ObjectInserter objInserter, ObjectReader objReader, RevWalk revWalk)
+      throws IOException {
     final Repository db = update.getRepository();
 
-    inserter = db.newObjectInserter();
-    reader = inserter.newReader();
-    final RevWalk rw = new RevWalk(reader);
+    inserter = objInserter == null ? db.newObjectInserter() : objInserter;
+    reader = objReader == null ? inserter.newReader() : objReader;
+    final RevWalk rw = revWalk == null ? new RevWalk(reader) : revWalk;
+
     final RevTree tree = revision != null ? rw.parseTree(revision) : null;
     newTree = readTree(tree);
     return new BatchMetaDataUpdate() {
@@ -379,13 +428,16 @@
       public void close() {
         newTree = null;
 
-        rw.close();
-        if (inserter != null) {
+        if (revWalk == null) {
+          rw.close();
+        }
+
+        if (objInserter == null && inserter != null) {
           inserter.close();
           inserter = null;
         }
 
-        if (reader != null) {
+        if (objReader == null && reader != null) {
           reader.close();
           reader = null;
         }
@@ -396,7 +448,9 @@
         BatchRefUpdate bru = update.getBatch();
         if (bru != null) {
           bru.addCommand(new ReceiveCommand(oldId.toObjectId(), newId.toObjectId(), refName));
-          inserter.flush();
+          if (objInserter == null) {
+            inserter.flush();
+          }
           revision = rw.parseCommit(newId);
           return revision;
         }
diff --git a/java/com/google/gerrit/server/index/IndexModule.java b/java/com/google/gerrit/server/index/IndexModule.java
index 6db00f5..17665c0 100644
--- a/java/com/google/gerrit/server/index/IndexModule.java
+++ b/java/com/google/gerrit/server/index/IndexModule.java
@@ -208,13 +208,14 @@
       return interactiveExecutor;
     }
     int threads = this.threads;
-    if (threads < 0) {
-      return MoreExecutors.newDirectExecutorService();
-    } else if (threads == 0) {
+    if (threads == 0) {
       threads =
           config.getInt(
               "index", null, "threads", Runtime.getRuntime().availableProcessors() / 2 + 1);
     }
+    if (threads < 0) {
+      return MoreExecutors.newDirectExecutorService();
+    }
     return MoreExecutors.listeningDecorator(
         workQueue.createQueue(threads, "Index-Interactive", true));
   }
@@ -227,11 +228,13 @@
     if (batchExecutor != null) {
       return batchExecutor;
     }
-    int threads = config.getInt("index", null, "batchThreads", 0);
+    int threads = this.threads;
+    if (threads == 0) {
+      threads =
+          config.getInt("index", null, "batchThreads", Runtime.getRuntime().availableProcessors());
+    }
     if (threads < 0) {
       return MoreExecutors.newDirectExecutorService();
-    } else if (threads == 0) {
-      threads = Runtime.getRuntime().availableProcessors();
     }
     return MoreExecutors.listeningDecorator(workQueue.createQueue(threads, "Index-Batch", true));
   }
diff --git a/java/com/google/gerrit/server/index/change/AllChangesIndexer.java b/java/com/google/gerrit/server/index/change/AllChangesIndexer.java
index 832dca6..01efe1a 100644
--- a/java/com/google/gerrit/server/index/change/AllChangesIndexer.java
+++ b/java/com/google/gerrit/server/index/change/AllChangesIndexer.java
@@ -134,6 +134,10 @@
         // splitting of repos into smaller parts reduced indexing time from 1.5 hours to 55 minutes
         // in 2020.
         int size = estimateSize(repo);
+        if (size == 0) {
+          pm.update(1);
+          continue;
+        }
         changeCount += size;
         int slices = 1 + size / PROJECT_SLICE_MAX_REFS;
         if (slices > 1) {
diff --git a/java/com/google/gerrit/server/index/options/AutoFlush.java b/java/com/google/gerrit/server/index/options/AutoFlush.java
new file mode 100644
index 0000000..7b82edb
--- /dev/null
+++ b/java/com/google/gerrit/server/index/options/AutoFlush.java
@@ -0,0 +1,20 @@
+// Copyright (C) 2021 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.index.options;
+
+public enum AutoFlush {
+  ENABLED,
+  DISABLED
+}
diff --git a/java/com/google/gerrit/server/mail/send/OutgoingEmail.java b/java/com/google/gerrit/server/mail/send/OutgoingEmail.java
index bef5317..a23c978 100644
--- a/java/com/google/gerrit/server/mail/send/OutgoingEmail.java
+++ b/java/com/google/gerrit/server/mail/send/OutgoingEmail.java
@@ -142,7 +142,8 @@
             // drop them from the recipient lists.
             //
             logger.atFine().log(
-                "Not CCing email sender %s because the email strategy of this user is not %s but %s",
+                "Not CCing email sender %s because the email strategy of this user is not %s but"
+                    + " %s",
                 fromUser.get().account().id(),
                 CC_ON_OWN_COMMENTS,
                 senderPrefs != null ? senderPrefs.getEmailStrategy() : null);
@@ -422,9 +423,13 @@
    * username. If no username is set, this function returns null.
    *
    * @param accountId user to fetch.
-   * @return name/email of account, username, or null if unset.
+   * @return name/email of account, username, or null if unset or the accountId is null.
    */
-  protected String getUserNameEmailFor(Account.Id accountId) {
+  protected String getUserNameEmailFor(@Nullable Account.Id accountId) {
+    if (accountId == null) {
+      return null;
+    }
+
     Optional<AccountState> accountState = args.accountCache.get(accountId);
     if (!accountState.isPresent()) {
       return null;
diff --git a/java/com/google/gerrit/server/restapi/project/GetAccess.java b/java/com/google/gerrit/server/restapi/project/GetAccess.java
index b572db3..a79439c 100644
--- a/java/com/google/gerrit/server/restapi/project/GetAccess.java
+++ b/java/com/google/gerrit/server/restapi/project/GetAccess.java
@@ -331,7 +331,7 @@
         }
         AccountGroup.UUID group = r.getGroup().getUUID();
         if (group != null) {
-          pInfo.rules.put(group.get(), info);
+          pInfo.rules.putIfAbsent(group.get(), info); // First entry for the group wins
           loadGroup(groups, group);
         }
       }
diff --git a/javatests/com/google/gerrit/acceptance/rest/project/AccessIT.java b/javatests/com/google/gerrit/acceptance/rest/project/AccessIT.java
index 33d0d29..caf9b90 100644
--- a/javatests/com/google/gerrit/acceptance/rest/project/AccessIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/project/AccessIT.java
@@ -23,6 +23,8 @@
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
 import static com.google.gerrit.truth.ConfigSubject.assertThat;
 import static com.google.gerrit.truth.MapSubject.assertThatMap;
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
 
 import com.google.gerrit.acceptance.AbstractDaemonTest;
 import com.google.gerrit.acceptance.ExtensionRegistry;
@@ -62,6 +64,7 @@
 import com.google.gerrit.server.schema.GrantRevertPermission;
 import com.google.inject.Inject;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
 import org.eclipse.jgit.junit.TestRepository;
@@ -941,6 +944,90 @@
     return gApi.projects().name(newProjectName.get());
   }
 
+  @Test
+  public void grantAllowAndDenyForSameGroup() throws Exception {
+    GroupReference registeredUsers = systemGroupBackend.getGroup(REGISTERED_USERS);
+    String access = "access";
+    List<String> allowThenDeny =
+        asList(registeredUsers.toConfigValue(), "deny " + registeredUsers.toConfigValue());
+    // Clone repository to forcefully add permission
+    TestRepository<InMemoryRepository> allProjectsRepo = cloneProject(allProjects, admin);
+
+    // Fetch permission ref
+    GitUtil.fetch(allProjectsRepo, "refs/meta/config:cfg");
+    allProjectsRepo.reset("cfg");
+
+    // Load current permissions
+    String config =
+        gApi.projects()
+            .name(allProjects.get())
+            .branch(RefNames.REFS_CONFIG)
+            .file(ProjectConfig.PROJECT_CONFIG)
+            .asString();
+
+    // Append and push allowThenDeny permissions
+    Config cfg = new Config();
+    cfg.fromText(config);
+    cfg.setStringList(access, AccessSection.HEADS, Permission.READ, allowThenDeny);
+    config = cfg.toText();
+    PushOneCommit push =
+        pushFactory.create(
+            admin.newIdent(), allProjectsRepo, "Subject", ProjectConfig.PROJECT_CONFIG, config);
+    push.to(RefNames.REFS_CONFIG).assertOkStatus();
+
+    ProjectAccessInfo pai = gApi.projects().name(allProjects.get()).access();
+    Map<String, AccessSectionInfo> local = pai.local;
+    AccessSectionInfo heads = local.get(AccessSection.HEADS);
+    Map<String, PermissionInfo> permissions = heads.permissions;
+    PermissionInfo read = permissions.get(Permission.READ);
+    Map<String, PermissionRuleInfo> rules = read.rules;
+    assertEquals(
+        rules.get(registeredUsers.getUUID().get()),
+        new PermissionRuleInfo(PermissionRuleInfo.Action.ALLOW, false));
+  }
+
+  @Test
+  public void grantDenyAndAllowForSameGroup() throws Exception {
+    GroupReference registeredUsers = systemGroupBackend.getGroup(REGISTERED_USERS);
+    String access = "access";
+    List<String> denyThenAllow =
+        asList("deny " + registeredUsers.toConfigValue(), registeredUsers.toConfigValue());
+    // Clone repository to forcefully add permission
+    TestRepository<InMemoryRepository> allProjectsRepo = cloneProject(allProjects, admin);
+
+    // Fetch permission ref
+    GitUtil.fetch(allProjectsRepo, "refs/meta/config:cfg");
+    allProjectsRepo.reset("cfg");
+
+    // Load current permissions
+    String config =
+        gApi.projects()
+            .name(allProjects.get())
+            .branch(RefNames.REFS_CONFIG)
+            .file(ProjectConfig.PROJECT_CONFIG)
+            .asString();
+
+    // Append and push denyThenAllow permissions
+    Config cfg = new Config();
+    cfg.fromText(config);
+    cfg.setStringList(access, AccessSection.HEADS, Permission.READ, denyThenAllow);
+    config = cfg.toText();
+    PushOneCommit push =
+        pushFactory.create(
+            admin.newIdent(), allProjectsRepo, "Subject", ProjectConfig.PROJECT_CONFIG, config);
+    push.to(RefNames.REFS_CONFIG).assertOkStatus();
+
+    ProjectAccessInfo pai = gApi.projects().name(allProjects.get()).access();
+    Map<String, AccessSectionInfo> local = pai.local;
+    AccessSectionInfo heads = local.get(AccessSection.HEADS);
+    Map<String, PermissionInfo> permissions = heads.permissions;
+    PermissionInfo read = permissions.get(Permission.READ);
+    Map<String, PermissionRuleInfo> rules = read.rules;
+    assertEquals(
+        rules.get(registeredUsers.getUUID().get()),
+        new PermissionRuleInfo(PermissionRuleInfo.Action.DENY, false));
+  }
+
   private ProjectAccessInput newProjectAccessInput() {
     ProjectAccessInput p = new ProjectAccessInput();
     p.add = new HashMap<>();
diff --git a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor.ts b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor.ts
index 1ab32ea..ac82547 100644
--- a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor.ts
+++ b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor.ts
@@ -25,7 +25,6 @@
 import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {htmlTemplate} from './gr-plugin-config-array-editor_html';
 import {property, customElement} from '@polymer/decorators';
-import {PolymerDeepPropertyChange} from '@polymer/polymer/interfaces';
 import {
   PluginConfigOptionsChangedEventDetail,
   ArrayPluginOption,
@@ -59,19 +58,8 @@
   @property({type: Object})
   pluginOption!: ArrayPluginOption;
 
-  @property({type: Boolean, computed: '_computeDisabled(pluginOption.*)'})
-  disabled?: boolean;
-
-  _computeDisabled(
-    record: PolymerDeepPropertyChange<ArrayPluginOption, ArrayPluginOption>
-  ) {
-    return !(
-      record &&
-      record.base &&
-      record.base.info &&
-      record.base.info.editable
-    );
-  }
+  @property({type: Boolean, reflectToAttribute: true})
+  disabled = false;
 
   _handleAddTap(e: MouseEvent) {
     e.preventDefault();
diff --git a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_html.ts b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_html.ts
index c96b86c..7709198 100644
--- a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_html.ts
+++ b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_html.ts
@@ -85,6 +85,7 @@
           id="input"
           on-keydown="_handleInputKeydown"
           bind-value="{{_newValue}}"
+          disabled$="[[disabled]]"
         />
       </iron-input>
       <gr-button
diff --git a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_test.js b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_test.js
index dfc191f..326ff44 100644
--- a/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_test.js
+++ b/polygerrit-ui/app/elements/admin/gr-plugin-config-array-editor/gr-plugin-config-array-editor_test.js
@@ -42,16 +42,6 @@
     assert.equal(element._computeShowInputRow(false), '');
   });
 
-  test('_computeDisabled', () => {
-    assert.isTrue(element._computeDisabled({}));
-    assert.isTrue(element._computeDisabled({base: {}}));
-    assert.isTrue(element._computeDisabled({base: {info: {}}}));
-    assert.isTrue(
-        element._computeDisabled({base: {info: {editable: false}}}));
-    assert.isFalse(
-        element._computeDisabled({base: {info: {editable: true}}}));
-  });
-
   suite('adding', () => {
     setup(() => {
       dispatchStub = sinon.stub(element, '_dispatchChanged');
@@ -60,11 +50,13 @@
     test('with enter', () => {
       element._newValue = '';
       MockInteractions.pressAndReleaseKeyOn(element.$.input, 13); // Enter
+      assert.isFalse(element.$.input.hasAttribute('disabled'));
       flush();
 
       assert.isFalse(dispatchStub.called);
       element._newValue = 'test';
       MockInteractions.pressAndReleaseKeyOn(element.$.input, 13); // Enter
+      assert.isFalse(element.$.input.hasAttribute('disabled'));
       flush();
 
       assert.isTrue(dispatchStub.called);
@@ -91,6 +83,7 @@
   test('deleting', () => {
     dispatchStub = sinon.stub(element, '_dispatchChanged');
     element.pluginOption = {info: {values: ['test', 'test2']}};
+    element.disabled = true;
     flush();
 
     const rows = getAll('.existingItems .row');
@@ -101,7 +94,7 @@
     flush();
 
     assert.isFalse(dispatchStub.called);
-    element.pluginOption.info.editable = true;
+    element.disabled = false;
     element.notifyPath('pluginOption.info.editable');
     flush();
 
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config.ts b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config.ts
index 880b397..e7eb9dc 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config.ts
@@ -84,6 +84,9 @@
   })
   _pluginConfigOptions!: PluginOption[]; // _computePluginConfigOptions never returns null
 
+  @property({type: Boolean, reflectToAttribute: true})
+  disabled = false;
+
   _computePluginConfigOptions(
     dataRecord: PolymerDeepPropertyChange<PluginData, PluginData>
   ): PluginOption[] {
@@ -117,8 +120,8 @@
     );
   }
 
-  _computeDisabled(editable: boolean) {
-    return !editable;
+  _computeDisabled(disabled: boolean, editable: boolean) {
+    return disabled || !editable;
   }
 
   _computeChecked(value = 'false') {
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_html.ts b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_html.ts
index 3045108..208e042 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_html.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_html.ts
@@ -55,6 +55,7 @@
               <gr-plugin-config-array-editor
                 on-plugin-config-option-changed="_handleArrayChange"
                 plugin-option="[[option]]"
+                disabled$="[[_computeDisabled(disabled, option.info.editable)]]"
               ></gr-plugin-config-array-editor>
             </template>
             <template is="dom-if" if="[[_isBoolean(option.info.type)]]">
@@ -62,7 +63,7 @@
                 checked="[[_computeChecked(option.info.value)]]"
                 on-change="_handleBooleanChange"
                 data-option-key$="[[option._key]]"
-                disabled$="[[_computeDisabled(option.info.editable)]]"
+                disabled$="[[_computeDisabled(disabled, option.info.editable)]]"
                 on-tap="_onTapPluginBoolean"
               ></paper-toggle-button>
             </template>
@@ -73,7 +74,7 @@
               >
                 <select
                   data-option-key$="[[option._key]]"
-                  disabled$="[[_computeDisabled(option.info.editable)]]"
+                  disabled$="[[_computeDisabled(disabled, option.info.editable)]]"
                 >
                   <template
                     is="dom-repeat"
@@ -90,14 +91,14 @@
                 bind-value="[[option.info.value]]"
                 on-input="_handleStringChange"
                 data-option-key$="[[option._key]]"
-                disabled$="[[_computeDisabled(option.info.editable)]]"
+                disabled$="[[_computeDisabled(disabled, option.info.editable)]]"
               >
                 <input
                   is="iron-input"
                   value="[[option.info.value]]"
                   on-input="_handleStringChange"
                   data-option-key$="[[option._key]]"
-                  disabled$="[[_computeDisabled(option.info.editable)]]"
+                  disabled$="[[_computeDisabled(disabled, option.info.editable)]]"
                 />
               </iron-input>
             </template>
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_test.js b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_test.js
index 28ef2f8..a5c7dfe 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_test.js
+++ b/polygerrit-ui/app/elements/admin/gr-repo-plugin-config/gr-repo-plugin-config_test.js
@@ -39,10 +39,11 @@
   });
 
   test('_computeDisabled', () => {
-    assert.isFalse(element._computeDisabled(true));
-    assert.isTrue(element._computeDisabled(undefined));
-    assert.isTrue(element._computeDisabled(null));
-    assert.isTrue(element._computeDisabled(false));
+    assert.isFalse(element._computeDisabled(false, true));
+    assert.isTrue(element._computeDisabled(false, undefined));
+    assert.isTrue(element._computeDisabled(false, null));
+    assert.isTrue(element._computeDisabled(false, false));
+    assert.isTrue(element._computeDisabled(true, true));
   });
 
   test('_handleChange', () => {
diff --git a/polygerrit-ui/app/elements/admin/gr-repo/gr-repo_html.ts b/polygerrit-ui/app/elements/admin/gr-repo/gr-repo_html.ts
index 2e86758..3d96f98 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo/gr-repo_html.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo/gr-repo_html.ts
@@ -414,6 +414,7 @@
             <template is="dom-repeat" items="[[_pluginData]]" as="data">
               <gr-repo-plugin-config
                 plugin-data="[[data]]"
+                disabled$="[[_readOnly]]"
               ></gr-repo-plugin-config>
             </template>
           </div>
diff --git a/resources/com/google/gerrit/httpd/auth/container/LoginRedirect.html b/resources/com/google/gerrit/httpd/auth/container/LoginRedirect.html
index 0567468..54c3661 100644
--- a/resources/com/google/gerrit/httpd/auth/container/LoginRedirect.html
+++ b/resources/com/google/gerrit/httpd/auth/container/LoginRedirect.html
@@ -4,6 +4,12 @@
     <title>Gerrit Code Review</title>
     <script type="text/javascript">
       var href = window.location.href;
+      var query = "";
+      var q = href.indexOf('?');
+      if (q >= 0) {
+        query = href.substring(q);
+        href = href.substring(0,q);
+      }
       var p = href.indexOf('#');
       var token;
       if (p >= 0) {
@@ -12,7 +18,7 @@
       } else {
         token = '';
       }
-      window.location.replace(href + 'login/' + token);
+      window.location.replace(href + 'login/' + token + query);
     </script>
   </head>
   <body>