diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 749d4c2..9885e71 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -3130,6 +3130,11 @@
 +
 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/java/com/google/gerrit/acceptance/GerritServer.java b/java/com/google/gerrit/acceptance/GerritServer.java
index a397923..b18df5b 100644
--- a/java/com/google/gerrit/acceptance/GerritServer.java
+++ b/java/com/google/gerrit/acceptance/GerritServer.java
@@ -35,6 +35,7 @@
 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.AutoFlush;
 import com.google.gerrit.server.ssh.NoSshModule;
 import com.google.gerrit.server.util.ManualRequestContext;
 import com.google.gerrit.server.util.OneOffRequestContext;
@@ -353,7 +354,8 @@
     cfg.setBoolean("index", null, "onlineUpgrade", false);
     cfg.setString("gitweb", null, "cgi", "");
     daemon.setEnableHttpd(desc.httpd());
-    daemon.setLuceneModule(LuceneIndexModule.singleVersionAllLatest(0, isSlave(baseConfig)));
+    daemon.setLuceneModule(
+        LuceneIndexModule.singleVersionAllLatest(0, isSlave(baseConfig), AutoFlush.ENABLED));
     daemon.setDatabaseForTesting(
         ImmutableList.<Module>of(
             new InMemoryTestingDatabaseModule(
diff --git a/java/com/google/gerrit/httpd/init/WebAppInitializer.java b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
index c2d4a14..9f2ecb4 100644
--- a/java/com/google/gerrit/httpd/init/WebAppInitializer.java
+++ b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
@@ -74,6 +74,7 @@
 import com.google.gerrit.server.git.GitRepositoryManagerModule;
 import com.google.gerrit.server.git.SearchingChangeCacheImpl;
 import com.google.gerrit.server.git.WorkQueue;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.IndexModule.IndexType;
 import com.google.gerrit.server.index.OnlineUpgrader;
@@ -387,7 +388,7 @@
   private Module createIndexModule() {
     switch (indexType) {
       case LUCENE:
-        return LuceneIndexModule.latestVersion(false);
+        return LuceneIndexModule.latestVersion(false, AutoFlush.ENABLED);
       case ELASTICSEARCH:
         return ElasticIndexModule.latestVersion(false);
       default:
diff --git a/java/com/google/gerrit/lucene/AbstractLuceneIndex.java b/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
index cb26488..ef42fe0 100644
--- a/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
+++ b/java/com/google/gerrit/lucene/AbstractLuceneIndex.java
@@ -39,6 +39,7 @@
 import com.google.gerrit.index.query.DataSource;
 import com.google.gerrit.index.query.FieldBundle;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.logging.LoggingContextAwareExecutorService;
 import com.google.gerrit.server.logging.LoggingContextAwareScheduledExecutorService;
@@ -103,6 +104,7 @@
   private final ReferenceManager<IndexSearcher> searcherManager;
   private final ControlledRealTimeReopenThread<IndexSearcher> reopenThread;
   private final Set<NrtFuture> notDoneNrtFutures;
+  private final AutoFlush autoFlush;
   private ScheduledExecutorService autoCommitExecutor;
 
   AbstractLuceneIndex(
@@ -112,12 +114,14 @@
       String name,
       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.autoFlush = autoFlush;
     String index = Joiner.on('_').skipNulls().join(name, subIndex);
     long commitPeriod = writerConfig.getCommitWithinMs();
 
@@ -211,7 +215,9 @@
           }
         });
 
-    reopenThread.start();
+    if (autoFlush.equals(AutoFlush.ENABLED)) {
+      reopenThread.start();
+    }
   }
 
   @Override
@@ -457,6 +463,9 @@
     }
 
     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 7d7cbef..5c78c34 100644
--- a/java/com/google/gerrit/lucene/ChangeSubIndex.java
+++ b/java/com/google/gerrit/lucene/ChangeSubIndex.java
@@ -29,6 +29,7 @@
 import com.google.gerrit.index.query.QueryParseException;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.change.ChangeField;
 import com.google.gerrit.server.index.change.ChangeIndex;
 import com.google.gerrit.server.query.change.ChangeData;
@@ -48,7 +49,8 @@
       SitePaths sitePaths,
       Path path,
       GerritIndexWriterConfig writerConfig,
-      SearcherFactory searcherFactory)
+      SearcherFactory searcherFactory,
+      AutoFlush autoFlush)
       throws IOException {
     this(
         schema,
@@ -56,7 +58,8 @@
         FSDirectory.open(path),
         path.getFileName().toString(),
         writerConfig,
-        searcherFactory);
+        searcherFactory,
+        autoFlush);
   }
 
   ChangeSubIndex(
@@ -65,9 +68,10 @@
       Directory dir,
       String subIndex,
       GerritIndexWriterConfig writerConfig,
-      SearcherFactory searcherFactory)
+      SearcherFactory searcherFactory,
+      AutoFlush autoFlush)
       throws IOException {
-    super(schema, sitePaths, dir, NAME, subIndex, writerConfig, searcherFactory);
+    super(schema, sitePaths, dir, NAME, subIndex, writerConfig, searcherFactory, autoFlush);
   }
 
   @Override
diff --git a/java/com/google/gerrit/lucene/LuceneAccountIndex.java b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
index 86a2111..84dd16d 100644
--- a/java/com/google/gerrit/lucene/LuceneAccountIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
@@ -31,6 +31,7 @@
 import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.index.account.AccountIndex;
 import com.google.inject.Inject;
@@ -86,7 +87,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<AccountCache> accountCache,
-      @Assisted Schema<AccountState> schema)
+      @Assisted Schema<AccountState> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -95,7 +97,8 @@
         ACCOUNTS,
         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 5194e5d..8c22dce 100644
--- a/java/com/google/gerrit/lucene/LuceneChangeIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneChangeIndex.java
@@ -50,6 +50,7 @@
 import com.google.gerrit.server.StarredChangesUtil;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexExecutor;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.index.change.ChangeField;
@@ -155,7 +156,8 @@
       @IndexExecutor(INTERACTIVE) ListeningExecutorService executor,
       Provider<ReviewDb> db,
       ChangeData.Factory changeDataFactory,
-      @Assisted Schema<ChangeData> schema)
+      @Assisted Schema<ChangeData> schema,
+      AutoFlush autoFlush)
       throws IOException {
     this.executor = executor;
     this.db = db;
@@ -171,18 +173,35 @@
     if (LuceneIndexModule.isInMemoryTest(cfg)) {
       openIndex =
           new ChangeSubIndex(
-              schema, sitePaths, new RAMDirectory(), "ramOpen", openConfig, searcherFactory);
+              schema,
+              sitePaths,
+              new RAMDirectory(),
+              "ramOpen",
+              openConfig,
+              searcherFactory,
+              autoFlush);
       closedIndex =
           new ChangeSubIndex(
-              schema, sitePaths, new RAMDirectory(), "ramClosed", closedConfig, searcherFactory);
+              schema,
+              sitePaths,
+              new RAMDirectory(),
+              "ramClosed",
+              closedConfig,
+              searcherFactory,
+              autoFlush);
     } else {
       Path dir = LuceneVersionManager.getDir(sitePaths, CHANGES, schema);
       openIndex =
           new ChangeSubIndex(
-              schema, sitePaths, dir.resolve(CHANGES_OPEN), openConfig, searcherFactory);
+              schema, sitePaths, dir.resolve(CHANGES_OPEN), openConfig, searcherFactory, autoFlush);
       closedIndex =
           new ChangeSubIndex(
-              schema, sitePaths, dir.resolve(CHANGES_CLOSED), closedConfig, searcherFactory);
+              schema,
+              sitePaths,
+              dir.resolve(CHANGES_CLOSED),
+              closedConfig,
+              searcherFactory,
+              autoFlush);
     }
   }
 
diff --git a/java/com/google/gerrit/lucene/LuceneGroupIndex.java b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
index 95e2ab9..40b455b 100644
--- a/java/com/google/gerrit/lucene/LuceneGroupIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
@@ -29,6 +29,7 @@
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.group.InternalGroup;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.index.group.GroupIndex;
 import com.google.inject.Inject;
@@ -82,7 +83,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<GroupCache> groupCache,
-      @Assisted Schema<InternalGroup> schema)
+      @Assisted Schema<InternalGroup> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -91,7 +93,8 @@
         GROUPS,
         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..10b58c0 100644
--- a/java/com/google/gerrit/lucene/LuceneIndexModule.java
+++ b/java/com/google/gerrit/lucene/LuceneIndexModule.java
@@ -19,6 +19,7 @@
 import com.google.gerrit.index.project.ProjectIndex;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.index.AbstractIndexModule;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.VersionManager;
 import com.google.gerrit.server.index.account.AccountIndex;
 import com.google.gerrit.server.index.change.ChangeIndex;
@@ -28,25 +29,36 @@
 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);
   }
 
   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 02d8655..5b2a2b7 100644
--- a/java/com/google/gerrit/lucene/LuceneProjectIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneProjectIndex.java
@@ -29,6 +29,7 @@
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.SitePaths;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexUtils;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
@@ -82,7 +83,8 @@
       @GerritServerConfig Config cfg,
       SitePaths sitePaths,
       Provider<ProjectCache> projectCache,
-      @Assisted Schema<ProjectData> schema)
+      @Assisted Schema<ProjectData> schema,
+      AutoFlush autoFlush)
       throws IOException {
     super(
         schema,
@@ -91,7 +93,8 @@
         PROJECTS,
         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 5f6015b..31735e6 100644
--- a/java/com/google/gerrit/pgm/Daemon.java
+++ b/java/com/google/gerrit/pgm/Daemon.java
@@ -83,6 +83,7 @@
 import com.google.gerrit.server.git.SearchingChangeCacheImpl;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.group.PeriodicGroupIndexer;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.IndexModule.IndexType;
 import com.google.gerrit.server.index.OnlineUpgrader;
@@ -529,7 +530,7 @@
     }
     switch (indexType) {
       case LUCENE:
-        return LuceneIndexModule.latestVersion(slave);
+        return LuceneIndexModule.latestVersion(slave, AutoFlush.ENABLED);
       case ELASTICSEARCH:
         return ElasticIndexModule.latestVersion(slave);
       default:
diff --git a/java/com/google/gerrit/pgm/Reindex.java b/java/com/google/gerrit/pgm/Reindex.java
index 85d1bd6..3789bc9 100644
--- a/java/com/google/gerrit/pgm/Reindex.java
+++ b/java/com/google/gerrit/pgm/Reindex.java
@@ -32,6 +32,7 @@
 import com.google.gerrit.pgm.util.ThreadLimiter;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.IndexModule.IndexType;
 import com.google.gerrit.server.index.change.ChangeSchemaDefinitions;
@@ -155,7 +156,9 @@
     Module indexModule;
     switch (IndexModule.getIndexType(dbInjector)) {
       case LUCENE:
-        indexModule = LuceneIndexModule.singleVersionWithExplicitVersions(versions, threads, slave);
+        indexModule =
+            LuceneIndexModule.singleVersionWithExplicitVersions(
+                versions, threads, slave, AutoFlush.DISABLED);
         break;
       case ELASTICSEARCH:
         indexModule =
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..54618a1 100644
--- a/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java
+++ b/java/com/google/gerrit/pgm/init/index/lucene/LuceneIndexModuleOnInit.java
@@ -17,6 +17,7 @@
 import com.google.gerrit.lucene.LuceneAccountIndex;
 import com.google.gerrit.lucene.LuceneGroupIndex;
 import com.google.gerrit.pgm.init.index.IndexModuleOnInit;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.account.AccountIndex;
 import com.google.gerrit.server.index.group.GroupIndex;
 import com.google.inject.AbstractModule;
@@ -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/index/AutoFlush.java b/java/com/google/gerrit/server/index/AutoFlush.java
new file mode 100644
index 0000000..3d13110
--- /dev/null
+++ b/java/com/google/gerrit/server/index/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;
+
+public enum AutoFlush {
+  ENABLED,
+  DISABLED
+}
diff --git a/java/com/google/gerrit/testing/InMemoryModule.java b/java/com/google/gerrit/testing/InMemoryModule.java
index 18dfea0..3a7b8b4 100644
--- a/java/com/google/gerrit/testing/InMemoryModule.java
+++ b/java/com/google/gerrit/testing/InMemoryModule.java
@@ -64,6 +64,7 @@
 import com.google.gerrit.server.git.PerThreadRequestScope;
 import com.google.gerrit.server.git.SearchingChangeCacheImpl;
 import com.google.gerrit.server.git.WorkQueue;
+import com.google.gerrit.server.index.AutoFlush;
 import com.google.gerrit.server.index.IndexModule.IndexType;
 import com.google.gerrit.server.index.account.AccountSchemaDefinitions;
 import com.google.gerrit.server.index.account.AllAccountsIndexer;
@@ -320,8 +321,13 @@
       boolean slave = cfg.getBoolean("container", "slave", false);
       Class<?> clazz = Class.forName(moduleClassName);
       Method m =
-          clazz.getMethod("singleVersionWithExplicitVersions", Map.class, int.class, boolean.class);
-      return (Module) m.invoke(null, getSingleSchemaVersions(), 0, slave);
+          clazz.getMethod(
+              "singleVersionWithExplicitVersions",
+              Map.class,
+              int.class,
+              boolean.class,
+              AutoFlush.class);
+      return (Module) m.invoke(null, getSingleSchemaVersions(), 0, slave, AutoFlush.ENABLED);
     } catch (ClassNotFoundException
         | SecurityException
         | NoSuchMethodException