diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index 47afdba..8509b1f 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -1425,8 +1425,7 @@
 any of their groups is used.
 
 This limit applies not only to the link:cmd-query.html[`gerrit query`]
-command, but also to the web UI results pagination size in the new
-PolyGerrit UI and, limited to the full project list, in the old GWT UI.
+command, but also to the web UI results pagination size.
 
 
 [[capability_readAs]]
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 8ad8669..1bf51a1 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -828,6 +828,49 @@
 +
 If 0 or negative, disk storage for the cache is disabled.
 
+[[cache.name.expireAfterWrite]]cache.<name>.expireAfterWrite::
++
+Duration after which a cached value will be evicted and not
+read anymore.
++
+Values should use common unit suffixes to express their setting:
++
+* ms, milliseconds
+* s, sec, second, seconds
+* m, min, minute, minutes
+* h, hr, hour, hours
++
+Disabled by default.
+
+[[cache.name.refreshAfterWrite]]cache.<name>.refreshAfterWrite::
++
+Duration after which we asynchronously refresh the cached value.
++
+Values should use common unit suffixes to express their setting:
++
+* ms, milliseconds
+* s, sec, second, seconds
+* m, min, minute, minutes
+* h, hr, hour, hours
++
+This applies only to these caches that support refreshing:
++
+* `"projects"`: Caching project information in-memory. Defaults to 15 minutes.
+
+[[cache.refreshThreadPoolSize]]cache.refreshThreadPoolSize::
++
+Number of threads that are available to refresh cached values that became
+out of date. This applies only to these caches that support refreshing:
++
+* `"projects"`: Caching project information in-memory
++
+Refreshes will only be scheduled on this executor if the values are
+out of sync.
+The check if they are is cheap and always happens on the thread that
+inquires for a cached value.
++
+Defaults to 2.
+
 ==== [[cache_names]]Standard Caches
 
 cache `"accounts"`::
@@ -1125,22 +1168,6 @@
 +
 Default is true, enabled.
 
-[[cache.projects.checkFrequency]]cache.projects.checkFrequency::
-+
-How often project configuration should be checked for update from Git.
-Gerrit Code Review caches project access rules and configuration in
-memory, checking the refs/meta/config branch every checkFrequency
-minutes to see if a new revision should be loaded and used for future
-access. Values can be specified using standard time unit abbreviations
-('ms', 'sec', 'min', etc.).
-+
-If set to 0, checks occur every time, which may slow down operations.
-If set to 'disabled' or 'off', no check will ever be done.
-Administrators may force the cache to flush with
-link:cmd-flush-caches.html[gerrit flush-caches].
-+
-Default is 5 minutes.
-
 [[cache.projects.loadOnStartup]]cache.projects.loadOnStartup::
 +
 If the project cache should be loaded during server startup.
diff --git a/Documentation/metrics.txt b/Documentation/metrics.txt
index 7e6799be..3040348 100644
--- a/Documentation/metrics.txt
+++ b/Documentation/metrics.txt
@@ -64,6 +64,7 @@
 * `caches/memory_eviction_count`: Memory eviction count.
 * `caches/disk_cached`: Disk entries used by persistent cache.
 * `caches/disk_hit_ratio`: Disk hit ratio for persistent cache.
+* `caches/refresh_count`: The number of refreshes per cache with an indicator if a reload was necessary.
 
 === Change
 
diff --git a/java/com/google/gerrit/acceptance/GerritServer.java b/java/com/google/gerrit/acceptance/GerritServer.java
index 0ef6ad5..2d62608 100644
--- a/java/com/google/gerrit/acceptance/GerritServer.java
+++ b/java/com/google/gerrit/acceptance/GerritServer.java
@@ -483,7 +483,6 @@
     cfg.setString("gerrit", null, "basePath", "git");
     cfg.setBoolean("sendemail", null, "enable", true);
     cfg.setInt("sendemail", null, "threadPoolSize", 0);
-    cfg.setInt("cache", "projects", "checkFrequency", 0);
     cfg.setInt("plugins", null, "checkFrequency", 0);
 
     cfg.setInt("sshd", null, "threads", 1);
diff --git a/java/com/google/gerrit/httpd/init/WebAppInitializer.java b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
index 05992d4..0c3b7b0 100644
--- a/java/com/google/gerrit/httpd/init/WebAppInitializer.java
+++ b/java/com/google/gerrit/httpd/init/WebAppInitializer.java
@@ -246,7 +246,7 @@
   }
 
   private boolean sshdOff() {
-    return new SshAddressesModule().getListenAddresses(config).isEmpty();
+    return new SshAddressesModule().provideListenAddresses(config).isEmpty();
   }
 
   private Injector createCfgInjector() {
diff --git a/java/com/google/gerrit/pgm/Daemon.java b/java/com/google/gerrit/pgm/Daemon.java
index 034e042e..57bec71 100644
--- a/java/com/google/gerrit/pgm/Daemon.java
+++ b/java/com/google/gerrit/pgm/Daemon.java
@@ -380,7 +380,7 @@
   }
 
   private boolean sshdOff() {
-    return new SshAddressesModule().getListenAddresses(config).isEmpty();
+    return new SshAddressesModule().provideListenAddresses(config).isEmpty();
   }
 
   private String myVersion() {
diff --git a/java/com/google/gerrit/server/CacheRefreshExecutor.java b/java/com/google/gerrit/server/CacheRefreshExecutor.java
new file mode 100644
index 0000000..1a377c3
--- /dev/null
+++ b/java/com/google/gerrit/server/CacheRefreshExecutor.java
@@ -0,0 +1,28 @@
+// Copyright (C) 2020 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;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import com.google.inject.BindingAnnotation;
+import java.lang.annotation.Retention;
+
+/**
+ * Marker on the global {@link java.util.concurrent.ThreadPoolExecutor} used to refresh outdated
+ * values in caches.
+ */
+@Retention(RUNTIME)
+@BindingAnnotation
+public @interface CacheRefreshExecutor {}
diff --git a/java/com/google/gerrit/server/cache/CacheBinding.java b/java/com/google/gerrit/server/cache/CacheBinding.java
index 9d90d073..99db64e 100644
--- a/java/com/google/gerrit/server/cache/CacheBinding.java
+++ b/java/com/google/gerrit/server/cache/CacheBinding.java
@@ -29,6 +29,13 @@
   /** Set the time an element lives after last access before being expired. */
   CacheBinding<K, V> expireFromMemoryAfterAccess(Duration duration);
 
+  /**
+   * Set the time that an element will be refreshed after. Elements older than this but younger than
+   * {@link #expireAfterWrite(Duration)} will still be returned, but on access a task is queued to
+   * refresh their value asynchronously.
+   */
+  CacheBinding<K, V> refreshAfterWrite(Duration duration);
+
   /** Populate the cache with items from the CacheLoader. */
   CacheBinding<K, V> loader(Class<? extends CacheLoader<K, V>> clazz);
 
diff --git a/java/com/google/gerrit/server/cache/CacheDef.java b/java/com/google/gerrit/server/cache/CacheDef.java
index d0c633e..31a453e 100644
--- a/java/com/google/gerrit/server/cache/CacheDef.java
+++ b/java/com/google/gerrit/server/cache/CacheDef.java
@@ -51,6 +51,9 @@
   Duration expireFromMemoryAfterAccess();
 
   @Nullable
+  Duration refreshAfterWrite();
+
+  @Nullable
   Weigher<K, V> weigher();
 
   @Nullable
diff --git a/java/com/google/gerrit/server/cache/CacheProvider.java b/java/com/google/gerrit/server/cache/CacheProvider.java
index fe4244c..2dd9e1f 100644
--- a/java/com/google/gerrit/server/cache/CacheProvider.java
+++ b/java/com/google/gerrit/server/cache/CacheProvider.java
@@ -38,6 +38,7 @@
   private long maximumWeight;
   private Duration expireAfterWrite;
   private Duration expireFromMemoryAfterAccess;
+  private Duration refreshAfterWrite;
   private Provider<CacheLoader<K, V>> loader;
   private Provider<Weigher<K, V>> weigher;
 
@@ -90,6 +91,13 @@
   }
 
   @Override
+  public CacheBinding<K, V> refreshAfterWrite(Duration duration) {
+    checkNotFrozen();
+    refreshAfterWrite = duration;
+    return this;
+  }
+
+  @Override
   public CacheBinding<K, V> loader(Class<? extends CacheLoader<K, V>> impl) {
     checkNotFrozen();
     loader = module.bindCacheLoader(this, impl);
@@ -151,6 +159,11 @@
   }
 
   @Override
+  public Duration refreshAfterWrite() {
+    return refreshAfterWrite;
+  }
+
+  @Override
   @Nullable
   public Weigher<K, V> weigher() {
     return weigher != null ? weigher.get() : null;
diff --git a/java/com/google/gerrit/server/cache/h2/H2CacheDefProxy.java b/java/com/google/gerrit/server/cache/h2/H2CacheDefProxy.java
index 5d9ce60..aa62745 100644
--- a/java/com/google/gerrit/server/cache/h2/H2CacheDefProxy.java
+++ b/java/com/google/gerrit/server/cache/h2/H2CacheDefProxy.java
@@ -43,6 +43,11 @@
   }
 
   @Override
+  public Duration refreshAfterWrite() {
+    return source.refreshAfterWrite();
+  }
+
+  @Override
   public Weigher<K, V> weigher() {
     Weigher<K, V> weigher = source.weigher();
     if (weigher == null) {
diff --git a/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java b/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
index 8f7e360..82615a4 100644
--- a/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
+++ b/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
@@ -237,6 +237,7 @@
         def.valueSerializer(),
         def.version(),
         maxSize,
-        def.expireAfterWrite());
+        def.expireAfterWrite(),
+        def.expireFromMemoryAfterAccess());
   }
 }
diff --git a/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java b/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
index ef4e44c..7a53600 100644
--- a/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
+++ b/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
@@ -23,6 +23,9 @@
 import com.google.common.collect.ImmutableSet;
 import com.google.common.flogger.FluentLogger;
 import com.google.common.hash.BloomFilter;
+import com.google.common.util.concurrent.FutureCallback;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.server.cache.PersistentCache;
 import com.google.gerrit.server.cache.serialize.CacheSerializer;
@@ -40,6 +43,7 @@
 import java.sql.Statement;
 import java.sql.Timestamp;
 import java.time.Duration;
+import java.time.Instant;
 import java.util.Calendar;
 import java.util.Map;
 import java.util.concurrent.ArrayBlockingQueue;
@@ -122,7 +126,12 @@
   @Override
   public V get(K key) throws ExecutionException {
     if (mem instanceof LoadingCache) {
-      return ((LoadingCache<K, ValueHolder<V>>) mem).get(key).value;
+      LoadingCache<K, ValueHolder<V>> asLoadingCache = (LoadingCache<K, ValueHolder<V>>) mem;
+      ValueHolder<V> valueHolder = asLoadingCache.get(key);
+      if (store.needsRefresh(valueHolder.created)) {
+        asLoadingCache.refresh(key);
+      }
+      return valueHolder.value;
     }
     throw new UnsupportedOperationException();
   }
@@ -139,8 +148,8 @@
                 }
               }
 
-              ValueHolder<V> h = new ValueHolder<>(valueLoader.call());
-              h.created = TimeUtil.nowMs();
+              ValueHolder<V> h =
+                  new ValueHolder<>(valueLoader.call(), Instant.ofEpochMilli(TimeUtil.nowMs()));
               executor.execute(() -> store.put(key, h));
               return h;
             })
@@ -149,8 +158,7 @@
 
   @Override
   public void put(K key, V val) {
-    final ValueHolder<V> h = new ValueHolder<>(val);
-    h.created = TimeUtil.nowMs();
+    final ValueHolder<V> h = new ValueHolder<>(val, Instant.ofEpochMilli(TimeUtil.nowMs()));
     mem.put(key, h);
     executor.execute(() -> store.put(key, h));
   }
@@ -217,11 +225,12 @@
 
   static class ValueHolder<V> {
     final V value;
-    long created;
+    final Instant created;
     volatile boolean clean;
 
-    ValueHolder(V value) {
+    ValueHolder(V value, Instant created) {
       this.value = value;
+      this.created = created;
     }
   }
 
@@ -248,12 +257,34 @@
           }
         }
 
-        final ValueHolder<V> h = new ValueHolder<>(loader.load(key));
-        h.created = TimeUtil.nowMs();
+        final ValueHolder<V> h =
+            new ValueHolder<>(loader.load(key), Instant.ofEpochMilli(TimeUtil.nowMs()));
         executor.execute(() -> store.put(key, h));
         return h;
       }
     }
+
+    @Override
+    public ListenableFuture<ValueHolder<V>> reload(K key, ValueHolder<V> oldValue)
+        throws Exception {
+      ListenableFuture<V> reloadedValue = loader.reload(key, oldValue.value);
+      Futures.addCallback(
+          reloadedValue,
+          new FutureCallback<V>() {
+            @Override
+            public void onSuccess(V result) {
+              store.put(key, new ValueHolder<>(result, TimeUtil.now()));
+            }
+
+            @Override
+            public void onFailure(Throwable t) {
+              logger.atWarning().withCause(t).log("Unable to reload cache value");
+            }
+          },
+          executor);
+
+      return Futures.transform(reloadedValue, v -> new ValueHolder<>(v, TimeUtil.now()), executor);
+    }
   }
 
   static class SqlStore<K, V> {
@@ -263,6 +294,7 @@
     private final int version;
     private final long maxSize;
     @Nullable private final Duration expireAfterWrite;
+    @Nullable private final Duration refreshAfterWrite;
     private final BlockingQueue<SqlHandle> handles;
     private final AtomicLong hitCount = new AtomicLong();
     private final AtomicLong missCount = new AtomicLong();
@@ -276,13 +308,15 @@
         CacheSerializer<V> valueSerializer,
         int version,
         long maxSize,
-        @Nullable Duration expireAfterWrite) {
+        @Nullable Duration expireAfterWrite,
+        @Nullable Duration refreshAfterWrite) {
       this.url = jdbcUrl;
       this.keyType = createKeyType(keyType, keySerializer);
       this.valueSerializer = valueSerializer;
       this.version = version;
       this.maxSize = maxSize;
       this.expireAfterWrite = expireAfterWrite;
+      this.refreshAfterWrite = refreshAfterWrite;
 
       int cores = Runtime.getRuntime().availableProcessors();
       int keep = Math.min(cores, 16);
@@ -394,14 +428,14 @@
           }
 
           Timestamp created = r.getTimestamp(2);
-          if (expired(created)) {
+          if (expired(created.toInstant())) {
             invalidate(key);
             missCount.incrementAndGet();
             return null;
           }
 
           V val = valueSerializer.deserialize(r.getBytes(1));
-          ValueHolder<V> h = new ValueHolder<>(val);
+          ValueHolder<V> h = new ValueHolder<>(val, created.toInstant());
           h.clean = true;
           hitCount.incrementAndGet();
           touch(c, key);
@@ -429,14 +463,22 @@
       return false;
     }
 
-    private boolean expired(Timestamp created) {
+    private boolean expired(Instant created) {
       if (expireAfterWrite == null) {
         return false;
       }
-      Duration age = Duration.between(created.toInstant(), TimeUtil.now());
+      Duration age = Duration.between(created, TimeUtil.now());
       return age.compareTo(expireAfterWrite) > 0;
     }
 
+    private boolean needsRefresh(Instant created) {
+      if (refreshAfterWrite == null) {
+        return false;
+      }
+      Duration age = Duration.between(created, TimeUtil.now());
+      return age.compareTo(refreshAfterWrite) > 0;
+    }
+
     private void touch(SqlHandle c, K key) throws IOException, SQLException {
       if (c.touch == null) {
         c.touch = c.conn.prepareStatement("UPDATE data SET accessed=? WHERE k=? AND version=?");
@@ -474,7 +516,7 @@
           keyType.set(c.put, 1, key);
           c.put.setBytes(2, valueSerializer.serialize(holder.value));
           c.put.setInt(3, version);
-          c.put.setTimestamp(4, new Timestamp(holder.created));
+          c.put.setTimestamp(4, Timestamp.from(holder.created));
           c.put.setTimestamp(5, TimeUtil.nowTs());
           c.put.executeUpdate();
           holder.clean = true;
@@ -560,7 +602,7 @@
             while (maxSize < used && r.next()) {
               K key = keyType.get(r, 1);
               Timestamp created = r.getTimestamp(3);
-              if (mem.getIfPresent(key) != null && !expired(created)) {
+              if (mem.getIfPresent(key) != null && !expired(created.toInstant())) {
                 touch(c, key);
               } else {
                 invalidate(c, key);
diff --git a/java/com/google/gerrit/server/cache/mem/DefaultMemoryCacheFactory.java b/java/com/google/gerrit/server/cache/mem/DefaultMemoryCacheFactory.java
index 9906b3d..23caca7 100644
--- a/java/com/google/gerrit/server/cache/mem/DefaultMemoryCacheFactory.java
+++ b/java/com/google/gerrit/server/cache/mem/DefaultMemoryCacheFactory.java
@@ -105,6 +105,21 @@
       builder.expireAfterAccess(expireAfterAccess.toNanos(), NANOSECONDS);
     }
 
+    Duration refreshAfterWrite = def.refreshAfterWrite();
+    if (has(def.configKey(), "refreshAfterWrite")) {
+      builder.refreshAfterWrite(
+          ConfigUtil.getTimeUnit(
+              cfg,
+              "cache",
+              def.configKey(),
+              "refreshAfterWrite",
+              toSeconds(refreshAfterWrite),
+              SECONDS),
+          SECONDS);
+    } else if (refreshAfterWrite != null) {
+      builder.refreshAfterWrite(refreshAfterWrite.toNanos(), NANOSECONDS);
+    }
+
     return builder;
   }
 
@@ -141,6 +156,21 @@
       builder.expireAfterAccess(expireAfterAccess.toNanos(), NANOSECONDS);
     }
 
+    Duration refreshAfterWrite = def.refreshAfterWrite();
+    if (has(def.configKey(), "refreshAfterWrite")) {
+      builder.expireAfterAccess(
+          ConfigUtil.getTimeUnit(
+              cfg,
+              "cache",
+              def.configKey(),
+              "refreshAfterWrite",
+              toSeconds(refreshAfterWrite),
+              SECONDS),
+          SECONDS);
+    } else if (refreshAfterWrite != null) {
+      builder.refreshAfterWrite(refreshAfterWrite.toNanos(), NANOSECONDS);
+    }
+
     return builder;
   }
 
diff --git a/java/com/google/gerrit/server/config/SysExecutorModule.java b/java/com/google/gerrit/server/config/SysExecutorModule.java
index e7f4540..ea45b12 100644
--- a/java/com/google/gerrit/server/config/SysExecutorModule.java
+++ b/java/com/google/gerrit/server/config/SysExecutorModule.java
@@ -14,7 +14,11 @@
 
 package com.google.gerrit.server.config;
 
+import static com.google.common.util.concurrent.MoreExecutors.newDirectExecutorService;
+
+import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.common.util.concurrent.MoreExecutors;
+import com.google.gerrit.server.CacheRefreshExecutor;
 import com.google.gerrit.server.FanOutExecutor;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.inject.AbstractModule;
@@ -24,7 +28,7 @@
 import org.eclipse.jgit.lib.Config;
 
 /**
- * Module providing the {@link ReceiveCommitsExecutor}.
+ * Module providing different executors.
  *
  * <p>This module is intended to be installed at the top level when creating a {@code sysInjector}
  * in {@code Daemon} or similar, not nested in another module. This ensures the module can be
@@ -37,7 +41,7 @@
   @Provides
   @Singleton
   @ReceiveCommitsExecutor
-  public ExecutorService createReceiveCommitsExecutor(
+  public ExecutorService provideReceiveCommitsExecutor(
       @GerritServerConfig Config config, WorkQueue queues) {
     int poolSize =
         config.getInt(
@@ -48,11 +52,11 @@
   @Provides
   @Singleton
   @SendEmailExecutor
-  public ExecutorService createSendEmailExecutor(
+  public ExecutorService provideSendEmailExecutor(
       @GerritServerConfig Config config, WorkQueue queues) {
     int poolSize = config.getInt("sendemail", null, "threadPoolSize", 1);
     if (poolSize == 0) {
-      return MoreExecutors.newDirectExecutorService();
+      return newDirectExecutorService();
     }
     return queues.createQueue(poolSize, "SendEmail", true);
   }
@@ -60,11 +64,24 @@
   @Provides
   @Singleton
   @FanOutExecutor
-  public ExecutorService createFanOutExecutor(@GerritServerConfig Config config, WorkQueue queues) {
+  public ExecutorService provideFanOutExecutor(
+      @GerritServerConfig Config config, WorkQueue queues) {
     int poolSize = config.getInt("execution", null, "fanOutThreadPoolSize", 25);
     if (poolSize == 0) {
-      return MoreExecutors.newDirectExecutorService();
+      return newDirectExecutorService();
     }
     return queues.createQueue(poolSize, "FanOut");
   }
+
+  @Provides
+  @Singleton
+  @CacheRefreshExecutor
+  public ListeningExecutorService provideCacheRefreshExecutor(
+      @GerritServerConfig Config config, WorkQueue queues) {
+    int poolSize = config.getInt("cache", null, "refreshThreadPoolSize", 2);
+    if (poolSize == 0) {
+      return newDirectExecutorService();
+    }
+    return MoreExecutors.listeningDecorator(queues.createQueue(poolSize, "CacheRefresh"));
+  }
 }
diff --git a/java/com/google/gerrit/server/config/UrlFormatter.java b/java/com/google/gerrit/server/config/UrlFormatter.java
index 8fc0d9e..d3f90e5 100644
--- a/java/com/google/gerrit/server/config/UrlFormatter.java
+++ b/java/com/google/gerrit/server/config/UrlFormatter.java
@@ -52,6 +52,11 @@
     return getChangeViewUrl(change.getProject(), change.getId()).map(url -> url + "?tab=comments");
   }
 
+  /** Returns the URL for viewing the findings tab view of a change. */
+  default Optional<String> getFindingsTabView(Change change) {
+    return getChangeViewUrl(change.getProject(), change.getId()).map(url -> url + "?tab=findings");
+  }
+
   /** Returns the URL for viewing a file in a given patch set of a change. */
   default Optional<String> getPatchFileView(Change change, int patchsetId, String filename) {
     return getChangeViewUrl(change.getProject(), change.getId())
diff --git a/java/com/google/gerrit/server/logging/Metadata.java b/java/com/google/gerrit/server/logging/Metadata.java
index 3bb4770..0a99d83 100644
--- a/java/com/google/gerrit/server/logging/Metadata.java
+++ b/java/com/google/gerrit/server/logging/Metadata.java
@@ -31,116 +31,123 @@
 /** Metadata that is provided to {@link PerformanceLogger}s as context for performance records. */
 @AutoValue
 public abstract class Metadata {
-  // The numeric ID of an account.
+  /** The numeric ID of an account. */
   public abstract Optional<Integer> accountId();
 
-  // The type of an action (ACCOUNT_UPDATE, CHANGE_UPDATE, GROUP_UPDATE, INDEX_QUERY,
-  // PLUGIN_UPDATE).
+  /**
+   * The type of an action (ACCOUNT_UPDATE, CHANGE_UPDATE, GROUP_UPDATE, INDEX_QUERY,
+   * PLUGIN_UPDATE).
+   */
   public abstract Optional<String> actionType();
 
-  // An authentication domain name.
+  /** An authentication domain name. */
   public abstract Optional<String> authDomainName();
 
-  // The name of a branch.
+  /** The name of a branch. */
   public abstract Optional<String> branchName();
 
-  // Key of an entity in a cache.
+  /** Key of an entity in a cache. */
   public abstract Optional<String> cacheKey();
 
-  // The name of a cache.
+  /** The name of a cache. */
   public abstract Optional<String> cacheName();
 
-  // The name of the implementation class.
+  /** The name of the implementation class. */
   public abstract Optional<String> className();
 
-  // The numeric ID of a change.
+  /** The numeric ID of a change. */
   public abstract Optional<Integer> changeId();
 
-  // The type of change ID which the user used to identify a change (e.g. numeric ID, triplet etc.).
+  /**
+   * The type of change ID which the user used to identify a change (e.g. numeric ID, triplet etc.).
+   */
   public abstract Optional<String> changeIdType();
 
-  // The cause of an error.
+  /** The cause of an error. */
   public abstract Optional<String> cause();
 
-  // The type of an event.
+  /** The type of an event. */
   public abstract Optional<String> eventType();
 
-  // The value of the @Export annotation which was used to register a plugin extension.
+  /** The value of the @Export annotation which was used to register a plugin extension. */
   public abstract Optional<String> exportValue();
 
-  // Path of a file in a repository.
+  /** Path of a file in a repository. */
   public abstract Optional<String> filePath();
 
-  // Garbage collector name.
+  /** Garbage collector name. */
   public abstract Optional<String> garbageCollectorName();
 
-  // Git operation (CLONE, FETCH).
+  /** Git operation (CLONE, FETCH). */
   public abstract Optional<String> gitOperation();
 
-  // The numeric ID of an internal group.
+  /** The numeric ID of an internal group. */
   public abstract Optional<Integer> groupId();
 
-  // The name of a group.
+  /** The name of a group. */
   public abstract Optional<String> groupName();
 
-  // The UUID of a group.
+  /** The UUID of a group. */
   public abstract Optional<String> groupUuid();
 
-  // HTTP status response code.
+  /** HTTP status response code. */
   public abstract Optional<Integer> httpStatus();
 
-  // The name of a secondary index.
+  /** The name of a secondary index. */
   public abstract Optional<String> indexName();
 
-  // The version of a secondary index.
+  /** The version of a secondary index. */
   public abstract Optional<Integer> indexVersion();
 
-  // The name of the implementation method.
+  /** The name of the implementation method. */
   public abstract Optional<String> methodName();
 
-  // One or more resources
+  /** One or more resources */
   public abstract Optional<Boolean> multiple();
 
-  // The name of an operation that is performed.
+  /** The name of an operation that is performed. */
   public abstract Optional<String> operationName();
 
-  // Partial or full computation
+  /** Partial or full computation */
   public abstract Optional<Boolean> partial();
 
-  // Path of a metadata file in NoteDb.
+  /** If a value is still current or not */
+  public abstract Optional<Boolean> outdated();
+
+  /** Path of a metadata file in NoteDb. */
   public abstract Optional<String> noteDbFilePath();
 
-  // Name of a metadata ref in NoteDb.
+  /** Name of a metadata ref in NoteDb. */
   public abstract Optional<String> noteDbRefName();
 
-  // Type of a sequence in NoteDb (ACCOUNTS, CHANGES, GROUPS).
+  /** Type of a sequence in NoteDb (ACCOUNTS, CHANGES, GROUPS). */
   public abstract Optional<String> noteDbSequenceType();
 
-  // The ID of a patch set.
+  /** The ID of a patch set. */
   public abstract Optional<Integer> patchSetId();
 
-  // Plugin metadata that doesn't fit into any other category.
+  /** Plugin metadata that doesn't fit into any other category. */
   public abstract ImmutableList<PluginMetadata> pluginMetadata();
 
-  // The name of a plugin.
+  /** The name of a plugin. */
   public abstract Optional<String> pluginName();
 
-  // The name of a Gerrit project (aka Git repository).
+  /** The name of a Gerrit project (aka Git repository). */
   public abstract Optional<String> projectName();
 
-  // The type of a Git push to Gerrit (CREATE_REPLACE, NORMAL, AUTOCLOSE).
+  /** The type of a Git push to Gerrit (CREATE_REPLACE, NORMAL, AUTOCLOSE). */
   public abstract Optional<String> pushType();
 
-  // The number of resources that is processed.
+  /** The number of resources that is processed. */
   public abstract Optional<Integer> resourceCount();
 
-  // The name of a REST view.
+  /** The name of a REST view. */
   public abstract Optional<String> restViewName();
 
-  // The SHA1 of Git commit.
+  /** The SHA1 of Git commit. */
   public abstract Optional<String> revision();
 
-  // The username of an account.
+  /** The username of an account. */
   public abstract Optional<String> username();
 
   /**
@@ -305,6 +312,8 @@
 
     public abstract Builder partial(boolean partial);
 
+    public abstract Builder outdated(boolean outdated);
+
     public abstract Builder noteDbFilePath(@Nullable String noteDbFilePath);
 
     public abstract Builder noteDbRefName(@Nullable String noteDbRefName);
diff --git a/java/com/google/gerrit/server/mail/send/CommentSender.java b/java/com/google/gerrit/server/mail/send/CommentSender.java
index deaa926..f3cccf2 100644
--- a/java/com/google/gerrit/server/mail/send/CommentSender.java
+++ b/java/com/google/gerrit/server/mail/send/CommentSender.java
@@ -93,6 +93,11 @@
       return args.urlFormatter.get().getCommentsTabView(change).orElse(null);
     }
 
+    /** @return a web link to the findings tab view of a change. */
+    public String getFindingsTabLink() {
+      return args.urlFormatter.get().getFindingsTabView(change).orElse(null);
+    }
+
     /**
      * @return A title for the group, i.e. "Commit Message", "Merge List", or "File [[filename]]".
      */
@@ -386,9 +391,7 @@
 
     for (CommentSender.FileCommentGroup group : getGroupedInlineComments(repo)) {
       Map<String, Object> groupData = new HashMap<>();
-      if (group.filename.equals(Patch.PATCHSET_LEVEL)) {
-        groupData.put("link", group.getCommentsTabLink());
-      } else {
+      if (!group.filename.equals(Patch.PATCHSET_LEVEL)) {
         groupData.put("link", group.getFileLink());
       }
       groupData.put("title", group.getTitle());
@@ -420,7 +423,11 @@
         // Set the comment link.
 
         if (comment.key.filename.equals(Patch.PATCHSET_LEVEL)) {
-          commentData.put("link", group.getCommentsTabLink());
+          if (comment instanceof RobotComment) {
+            commentData.put("link", group.getFindingsTabLink());
+          } else {
+            commentData.put("link", group.getCommentsTabLink());
+          }
         } else if (comment.lineNbr == 0) {
           commentData.put("link", group.getFileLink());
         } else {
diff --git a/java/com/google/gerrit/server/notedb/DeleteZombieCommentsRefs.java b/java/com/google/gerrit/server/notedb/DeleteZombieCommentsRefs.java
index 128e185..1ead03c 100644
--- a/java/com/google/gerrit/server/notedb/DeleteZombieCommentsRefs.java
+++ b/java/com/google/gerrit/server/notedb/DeleteZombieCommentsRefs.java
@@ -27,6 +27,7 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
 import org.eclipse.jgit.lib.BatchRefUpdate;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
@@ -47,12 +48,16 @@
 
   private static final String EMPTY_TREE_ID = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
   private static final String DRAFT_REFS_PREFIX = "refs/draft-comments";
-  private static final int CHUNK_SIZE = 100; // log progress after deleting every CHUNK_SIZE refs
+
+  // Number of refs deleted at once in a batch ref-update.
+  // Log progress after deleting every CHUNK_SIZE refs
+  private static final int CHUNK_SIZE = 3000;
 
   private final GitRepositoryManager repoManager;
   private final AllUsersName allUsers;
   private final int cleanupPercentage;
   private Repository allUsersRepo;
+  private final Consumer<String> uiConsumer;
 
   public interface Factory {
     DeleteZombieCommentsRefs create(int cleanupPercentage);
@@ -63,9 +68,18 @@
       AllUsersName allUsers,
       GitRepositoryManager repoManager,
       @Assisted Integer cleanupPercentage) {
+    this(allUsers, repoManager, cleanupPercentage, (msg) -> {});
+  }
+
+  public DeleteZombieCommentsRefs(
+      AllUsersName allUsers,
+      GitRepositoryManager repoManager,
+      Integer cleanupPercentage,
+      Consumer<String> uiConsumer) {
     this.allUsers = allUsers;
     this.repoManager = repoManager;
     this.cleanupPercentage = (cleanupPercentage == null) ? 100 : cleanupPercentage;
+    this.uiConsumer = uiConsumer;
   }
 
   public void execute() throws IOException {
@@ -74,15 +88,17 @@
     List<Ref> draftRefs = allUsersRepo.getRefDatabase().getRefsByPrefix(DRAFT_REFS_PREFIX);
     List<Ref> zombieRefs = filterZombieRefs(draftRefs);
 
-    logger.atInfo().log(
-        "Found a total of %d zombie draft refs in %s repo.", zombieRefs.size(), allUsers.get());
+    logInfo(
+        String.format(
+            "Found a total of %d zombie draft refs in %s repo.",
+            zombieRefs.size(), allUsers.get()));
 
-    logger.atInfo().log("Cleanup percentage = %d", cleanupPercentage);
+    logInfo(String.format("Cleanup percentage = %d", cleanupPercentage));
     zombieRefs =
         zombieRefs.stream()
             .filter(ref -> Change.Id.fromAllUsersRef(ref.getName()).get() % 100 < cleanupPercentage)
             .collect(toImmutableList());
-    logger.atInfo().log("Number of zombie refs to be cleaned = %d", zombieRefs.size());
+    logInfo(String.format("Number of zombie refs to be cleaned = %d", zombieRefs.size()));
 
     long zombieRefsCnt = zombieRefs.size();
     long deletedRefsCnt = 0;
@@ -124,8 +140,15 @@
     return allUsersRepo.parseCommit(ref.getObjectId()).getTree().getName().equals(EMPTY_TREE_ID);
   }
 
+  private void logInfo(String message) {
+    logger.atInfo().log(message);
+    uiConsumer.accept(message);
+  }
+
   private void logProgress(long deletedRefsCount, long allRefsCount, long elapsed) {
-    logger.atInfo().log(
-        "Deleted %d/%d zombie draft refs (%d seconds)\n", deletedRefsCount, allRefsCount, elapsed);
+    logInfo(
+        String.format(
+            "Deleted %d/%d zombie draft refs (%d seconds)",
+            deletedRefsCount, allRefsCount, elapsed));
   }
 }
diff --git a/java/com/google/gerrit/server/patch/DiffExecutorModule.java b/java/com/google/gerrit/server/patch/DiffExecutorModule.java
index eb6a280..b9e644f 100644
--- a/java/com/google/gerrit/server/patch/DiffExecutorModule.java
+++ b/java/com/google/gerrit/server/patch/DiffExecutorModule.java
@@ -31,7 +31,7 @@
   @Provides
   @Singleton
   @DiffExecutor
-  public ExecutorService createDiffExecutor() {
+  public ExecutorService provideDiffExecutor() {
     return new LoggingContextAwareExecutorService(
         Executors.newCachedThreadPool(
             new ThreadFactoryBuilder().setNameFormat("Diff-%d").setDaemon(true).build()));
diff --git a/java/com/google/gerrit/server/project/ProjectCacheClock.java b/java/com/google/gerrit/server/project/ProjectCacheClock.java
deleted file mode 100644
index eb451fd..0000000
--- a/java/com/google/gerrit/server/project/ProjectCacheClock.java
+++ /dev/null
@@ -1,100 +0,0 @@
-// Copyright (C) 2012 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.project;
-
-import com.google.common.util.concurrent.ThreadFactoryBuilder;
-import com.google.gerrit.extensions.events.LifecycleListener;
-import com.google.gerrit.server.config.ConfigUtil;
-import com.google.gerrit.server.config.GerritServerConfig;
-import com.google.gerrit.server.logging.LoggingContextAwareScheduledExecutorService;
-import com.google.inject.Inject;
-import com.google.inject.Singleton;
-import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicLong;
-import org.eclipse.jgit.lib.Config;
-
-/** Ticks periodically to force refresh events for {@link ProjectCacheImpl}. */
-@Singleton
-public class ProjectCacheClock implements LifecycleListener {
-  private final Config serverConfig;
-
-  private final AtomicLong generation = new AtomicLong();
-
-  private ScheduledExecutorService executor;
-
-  @Inject
-  public ProjectCacheClock(@GerritServerConfig Config serverConfig) {
-    this.serverConfig = serverConfig;
-  }
-
-  @Override
-  public void start() {
-    long checkFrequencyMillis = checkFrequency(serverConfig);
-
-    if (checkFrequencyMillis == Long.MAX_VALUE) {
-      // Start with generation 1 (to avoid magic 0 below).
-      // Do not begin background thread, disabling the clock.
-      generation.set(1);
-    } else if (10 < checkFrequencyMillis) {
-      // Start with generation 1 (to avoid magic 0 below).
-      generation.set(1);
-      executor =
-          new LoggingContextAwareScheduledExecutorService(
-              Executors.newScheduledThreadPool(
-                  1,
-                  new ThreadFactoryBuilder()
-                      .setNameFormat("ProjectCacheClock-%d")
-                      .setDaemon(true)
-                      .setPriority(Thread.MIN_PRIORITY)
-                      .build()));
-      @SuppressWarnings("unused") // Runnable already handles errors
-      Future<?> possiblyIgnoredError =
-          executor.scheduleAtFixedRate(
-              generation::incrementAndGet,
-              checkFrequencyMillis,
-              checkFrequencyMillis,
-              TimeUnit.MILLISECONDS);
-    } else {
-      // Magic generation 0 triggers ProjectState to always
-      // check on each needsRefresh() request we make to it.
-      generation.set(0);
-    }
-  }
-
-  @Override
-  public void stop() {
-    if (executor != null) {
-      executor.shutdown();
-    }
-  }
-
-  long read() {
-    return generation.get();
-  }
-
-  private static long checkFrequency(Config serverConfig) {
-    String freq = serverConfig.getString("cache", "projects", "checkFrequency");
-    if (freq != null && ("disabled".equalsIgnoreCase(freq) || "off".equalsIgnoreCase(freq))) {
-      return Long.MAX_VALUE;
-    }
-    return TimeUnit.MILLISECONDS.convert(
-        ConfigUtil.getTimeUnit(
-            serverConfig, "cache", "projects", "checkFrequency", 5, TimeUnit.MINUTES),
-        TimeUnit.MINUTES);
-  }
-}
diff --git a/java/com/google/gerrit/server/project/ProjectCacheImpl.java b/java/com/google/gerrit/server/project/ProjectCacheImpl.java
index 9d09eeb..a5c07e5 100644
--- a/java/com/google/gerrit/server/project/ProjectCacheImpl.java
+++ b/java/com/google/gerrit/server/project/ProjectCacheImpl.java
@@ -24,16 +24,23 @@
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.Sets;
 import com.google.common.flogger.FluentLogger;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.entities.AccountGroup;
 import com.google.gerrit.entities.Project;
+import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.index.project.ProjectIndexer;
 import com.google.gerrit.lifecycle.LifecycleModule;
+import com.google.gerrit.metrics.Counter2;
 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.server.CacheRefreshExecutor;
 import com.google.gerrit.server.cache.CacheModule;
 import com.google.gerrit.server.config.AllProjectsName;
 import com.google.gerrit.server.config.AllUsersName;
@@ -48,6 +55,7 @@
 import com.google.inject.TypeLiteral;
 import com.google.inject.name.Named;
 import java.io.IOException;
+import java.time.Duration;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
@@ -55,6 +63,7 @@
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
+import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 
 /** Cache of project information, including access rights. */
@@ -70,7 +79,10 @@
     return new CacheModule() {
       @Override
       protected void configure() {
-        cache(CACHE_NAME, String.class, ProjectState.class).loader(Loader.class);
+        cache(CACHE_NAME, Project.NameKey.class, ProjectState.class)
+            .loader(Loader.class)
+            .refreshAfterWrite(Duration.ofMinutes(15))
+            .expireAfterWrite(Duration.ofHours(1));
 
         cache(CACHE_LIST, ListKey.class, new TypeLiteral<ImmutableSortedSet<Project.NameKey>>() {})
             .maximumWeight(1)
@@ -84,7 +96,6 @@
               @Override
               protected void configure() {
                 listener().to(ProjectCacheWarmer.class);
-                listener().to(ProjectCacheClock.class);
               }
             });
       }
@@ -93,10 +104,9 @@
 
   private final AllProjectsName allProjectsName;
   private final AllUsersName allUsersName;
-  private final LoadingCache<String, ProjectState> byName;
+  private final LoadingCache<Project.NameKey, ProjectState> byName;
   private final LoadingCache<ListKey, ImmutableSortedSet<Project.NameKey>> list;
   private final Lock listLock;
-  private final ProjectCacheClock clock;
   private final Provider<ProjectIndexer> indexer;
   private final Timer0 guessRelevantGroupsLatency;
 
@@ -104,9 +114,8 @@
   ProjectCacheImpl(
       final AllProjectsName allProjectsName,
       final AllUsersName allUsersName,
-      @Named(CACHE_NAME) LoadingCache<String, ProjectState> byName,
+      @Named(CACHE_NAME) LoadingCache<Project.NameKey, ProjectState> byName,
       @Named(CACHE_LIST) LoadingCache<ListKey, ImmutableSortedSet<Project.NameKey>> list,
-      ProjectCacheClock clock,
       Provider<ProjectIndexer> indexer,
       MetricMaker metricMaker) {
     this.allProjectsName = allProjectsName;
@@ -114,7 +123,6 @@
     this.byName = byName;
     this.list = list;
     this.listLock = new ReentrantLock(true /* fair */);
-    this.clock = clock;
     this.indexer = indexer;
 
     this.guessRelevantGroupsLatency =
@@ -142,13 +150,8 @@
     }
 
     try {
-      ProjectState state = byName.get(projectName.get());
-      if (state != null && state.needsRefresh(clock.read())) {
-        byName.invalidate(projectName.get());
-        state = byName.get(projectName.get());
-      }
-      return Optional.of(state);
-    } catch (Exception e) {
+      return Optional.of(byName.get(projectName));
+    } catch (ExecutionException e) {
       if ((e.getCause() instanceof RepositoryNotFoundException)) {
         logger.atFine().log("Cannot find project %s", projectName.get());
         return Optional.empty();
@@ -167,7 +170,7 @@
   public void evict(Project.NameKey p) {
     if (p != null) {
       logger.atFine().log("Evict project '%s'", p.get());
-      byName.invalidate(p.get());
+      byName.invalidate(p);
     }
     indexer.get().index(p);
   }
@@ -222,7 +225,7 @@
   public Set<AccountGroup.UUID> guessRelevantGroupUUIDs() {
     try (Timer0.Context ignored = guessRelevantGroupsLatency.start()) {
       return all().stream()
-          .map(n -> byName.getIfPresent(n.get()))
+          .map(n -> byName.getIfPresent(n))
           .filter(Objects::nonNull)
           .flatMap(p -> p.getConfig().getAllGroupUUIDs().stream())
           // getAllGroupUUIDs shouldn't really return null UUIDs, but harden
@@ -245,41 +248,67 @@
     }
   }
 
-  static class Loader extends CacheLoader<String, ProjectState> {
+  @Singleton
+  static class Loader extends CacheLoader<Project.NameKey, ProjectState> {
     private final ProjectState.Factory projectStateFactory;
     private final GitRepositoryManager mgr;
-    private final ProjectCacheClock clock;
     private final ProjectConfig.Factory projectConfigFactory;
+    private final ListeningExecutorService cacheRefreshExecutor;
+    private final Counter2<String, Boolean> refreshCounter;
 
     @Inject
     Loader(
         ProjectState.Factory psf,
         GitRepositoryManager g,
-        ProjectCacheClock clock,
-        ProjectConfig.Factory projectConfigFactory) {
+        ProjectConfig.Factory projectConfigFactory,
+        @CacheRefreshExecutor ListeningExecutorService cacheRefreshExecutor,
+        MetricMaker metricMaker) {
       projectStateFactory = psf;
       mgr = g;
-      this.clock = clock;
       this.projectConfigFactory = projectConfigFactory;
+      this.cacheRefreshExecutor = cacheRefreshExecutor;
+      refreshCounter =
+          metricMaker.newCounter(
+              "caches/refresh_count",
+              new Description("count").setRate(),
+              Field.ofString("cache", Metadata.Builder::className).build(),
+              Field.ofBoolean("outdated", Metadata.Builder::outdated).build());
     }
 
     @Override
-    public ProjectState load(String projectName) throws Exception {
+    public ProjectState load(Project.NameKey key) throws Exception {
       try (TraceTimer timer =
           TraceContext.newTimer(
-              "Loading project", Metadata.builder().projectName(projectName).build())) {
-        long now = clock.read();
-        Project.NameKey key = Project.nameKey(projectName);
+              "Loading project", Metadata.builder().projectName(key.get()).build())) {
         try (Repository git = mgr.openRepository(key)) {
           ProjectConfig cfg = projectConfigFactory.create(key);
           cfg.load(key, git);
-
-          ProjectState state = projectStateFactory.create(cfg);
-          state.initLastCheck(now);
-          return state;
+          return projectStateFactory.create(cfg);
         }
       }
     }
+
+    @Override
+    public ListenableFuture<ProjectState> reload(Project.NameKey key, ProjectState oldState)
+        throws Exception {
+      try (TraceTimer timer =
+          TraceContext.newTimer(
+              "Reload project", Metadata.builder().projectName(key.get()).build())) {
+        try (Repository git = mgr.openRepository(key)) {
+          Ref configRef = git.exactRef(RefNames.REFS_CONFIG);
+          if (configRef != null
+              && configRef.getObjectId().equals(oldState.getConfig().getRevision())) {
+            refreshCounter.increment(CACHE_NAME, false);
+            return Futures.immediateFuture(oldState);
+          }
+        }
+
+        // Repository is not thread safe, so we have to open it on the thread that does the loading.
+        // Just invoke the loader on the other thread.
+        refreshCounter.increment(CACHE_NAME, true);
+        return cacheRefreshExecutor.submit(() -> load(key));
+      }
+    }
   }
 
   static class ListKey {
diff --git a/java/com/google/gerrit/server/project/ProjectState.java b/java/com/google/gerrit/server/project/ProjectState.java
index e52f344..efadcc8 100644
--- a/java/com/google/gerrit/server/project/ProjectState.java
+++ b/java/com/google/gerrit/server/project/ProjectState.java
@@ -32,7 +32,6 @@
 import com.google.gerrit.entities.BooleanProjectConfig;
 import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.entities.Project;
-import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.api.projects.CommentLinkInfo;
 import com.google.gerrit.extensions.client.SubmitType;
 import com.google.gerrit.extensions.restapi.ResourceConflictException;
@@ -59,7 +58,6 @@
 import java.util.Optional;
 import java.util.Set;
 import org.eclipse.jgit.errors.ConfigInvalidException;
-import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 
 /**
@@ -86,9 +84,6 @@
   private final long globalMaxObjectSizeLimit;
   private final boolean inheritProjectMaxObjectSizeLimit;
 
-  /** Last system time the configuration's revision was examined. */
-  private volatile long lastCheckGeneration;
-
   /** Local access sections, wrapped in SectionMatchers for faster evaluation. */
   private volatile List<SectionMatcher> localAccessSections;
 
@@ -140,33 +135,6 @@
     }
   }
 
-  void initLastCheck(long generation) {
-    lastCheckGeneration = generation;
-  }
-
-  boolean needsRefresh(long generation) {
-    if (generation <= 0) {
-      return isRevisionOutOfDate();
-    }
-    if (lastCheckGeneration != generation) {
-      lastCheckGeneration = generation;
-      return isRevisionOutOfDate();
-    }
-    return false;
-  }
-
-  private boolean isRevisionOutOfDate() {
-    try (Repository git = gitMgr.openRepository(getNameKey())) {
-      Ref ref = git.getRefDatabase().exactRef(RefNames.REFS_CONFIG);
-      if (ref == null || ref.getObjectId() == null) {
-        return true;
-      }
-      return !ref.getObjectId().equals(config.getRevision());
-    } catch (IOException gone) {
-      return true;
-    }
-  }
-
   /**
    * @return cached computation of all global capabilities. This should only be invoked on the state
    *     from {@link ProjectCache#getAllProjects()}. Null on any other project.
diff --git a/java/com/google/gerrit/server/schema/Schema_182.java b/java/com/google/gerrit/server/schema/Schema_182.java
index 3928b2b..a61a175 100644
--- a/java/com/google/gerrit/server/schema/Schema_182.java
+++ b/java/com/google/gerrit/server/schema/Schema_182.java
@@ -28,7 +28,8 @@
   public void upgrade(Arguments args, UpdateUI ui) throws Exception {
     AllUsersName allUsers = args.allUsers;
     GitRepositoryManager gitRepoManager = args.repoManager;
-    DeleteZombieCommentsRefs cleanup = new DeleteZombieCommentsRefs(allUsers, gitRepoManager, 100);
+    DeleteZombieCommentsRefs cleanup =
+        new DeleteZombieCommentsRefs(allUsers, gitRepoManager, 100, ui::message);
     cleanup.execute();
   }
 }
diff --git a/java/com/google/gerrit/server/ssh/SshAddressesModule.java b/java/com/google/gerrit/server/ssh/SshAddressesModule.java
index 0a6bcac..1159e06 100644
--- a/java/com/google/gerrit/server/ssh/SshAddressesModule.java
+++ b/java/com/google/gerrit/server/ssh/SshAddressesModule.java
@@ -40,7 +40,7 @@
   @Provides
   @Singleton
   @SshListenAddresses
-  public List<SocketAddress> getListenAddresses(@GerritServerConfig Config cfg) {
+  public List<SocketAddress> provideListenAddresses(@GerritServerConfig Config cfg) {
     List<SocketAddress> listen = Lists.newArrayListWithExpectedSize(2);
     String[] want = cfg.getStringList("sshd", null, "listenaddress");
     if (want == null || want.length == 0) {
@@ -71,7 +71,7 @@
   @Provides
   @Singleton
   @SshAdvertisedAddresses
-  List<String> getAdvertisedAddresses(
+  List<String> provideAdvertisedAddresses(
       @GerritServerConfig Config cfg, @SshListenAddresses List<SocketAddress> listen) {
     String[] want = cfg.getStringList("sshd", null, "advertisedaddress");
     if (want.length > 0) {
diff --git a/java/com/google/gerrit/testing/InMemoryModule.java b/java/com/google/gerrit/testing/InMemoryModule.java
index 8800463..a682d33 100644
--- a/java/com/google/gerrit/testing/InMemoryModule.java
+++ b/java/com/google/gerrit/testing/InMemoryModule.java
@@ -15,10 +15,11 @@
 package com.google.gerrit.testing;
 
 import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.util.concurrent.MoreExecutors.newDirectExecutorService;
 import static com.google.inject.Scopes.SINGLETON;
 
 import com.google.common.base.Strings;
-import com.google.common.util.concurrent.MoreExecutors;
+import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperationsImpl;
 import com.google.gerrit.extensions.client.AuthType;
@@ -30,6 +31,7 @@
 import com.google.gerrit.index.project.ProjectSchemaDefinitions;
 import com.google.gerrit.metrics.DisabledMetricMaker;
 import com.google.gerrit.metrics.MetricMaker;
+import com.google.gerrit.server.CacheRefreshExecutor;
 import com.google.gerrit.server.FanOutExecutor;
 import com.google.gerrit.server.GerritPersonIdent;
 import com.google.gerrit.server.GerritPersonIdentProvider;
@@ -209,7 +211,7 @@
           @Singleton
           @DiffExecutor
           public ExecutorService createDiffExecutor() {
-            return MoreExecutors.newDirectExecutorService();
+            return newDirectExecutorService();
           }
         });
     install(new DefaultMemoryCacheModule());
@@ -277,7 +279,7 @@
   @Singleton
   @SendEmailExecutor
   public ExecutorService createSendEmailExecutor() {
-    return MoreExecutors.newDirectExecutorService();
+    return newDirectExecutorService();
   }
 
   @Provides
@@ -287,6 +289,13 @@
     return queues.createQueue(2, "FanOut");
   }
 
+  @Provides
+  @Singleton
+  @CacheRefreshExecutor
+  public ListeningExecutorService createCacheRefreshExecutor() {
+    return newDirectExecutorService();
+  }
+
   private Module luceneIndexModule() {
     return indexModule("com.google.gerrit.lucene.LuceneIndexModule");
   }
diff --git a/javatests/com/google/gerrit/server/cache/h2/BUILD b/javatests/com/google/gerrit/server/cache/h2/BUILD
index 98f1b0e..438990c 100644
--- a/javatests/com/google/gerrit/server/cache/h2/BUILD
+++ b/javatests/com/google/gerrit/server/cache/h2/BUILD
@@ -6,10 +6,12 @@
     deps = [
         "//java/com/google/gerrit/server/cache/h2",
         "//java/com/google/gerrit/server/cache/serialize",
+        "//java/com/google/gerrit/server/util/time",
         "//lib:guava",
         "//lib:h2",
         "//lib:junit",
         "//lib/guice",
+        "//lib/mockito",
         "//lib/truth",
     ],
 )
diff --git a/javatests/com/google/gerrit/server/cache/h2/H2CacheTest.java b/javatests/com/google/gerrit/server/cache/h2/H2CacheTest.java
index 69c2799..fb3a0db 100644
--- a/javatests/com/google/gerrit/server/cache/h2/H2CacheTest.java
+++ b/javatests/com/google/gerrit/server/cache/h2/H2CacheTest.java
@@ -16,16 +16,27 @@
 
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth.assertWithMessage;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+import static org.mockito.Mockito.when;
 
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
+import com.google.common.cache.LoadingCache;
+import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.MoreExecutors;
 import com.google.gerrit.server.cache.h2.H2CacheImpl.SqlStore;
 import com.google.gerrit.server.cache.h2.H2CacheImpl.ValueHolder;
 import com.google.gerrit.server.cache.serialize.StringCacheSerializer;
+import com.google.gerrit.server.util.time.TimeUtil;
 import com.google.inject.TypeLiteral;
+import java.time.Duration;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
+import javax.annotation.Nullable;
 import org.junit.Test;
 
 public class H2CacheTest {
@@ -38,23 +49,31 @@
   }
 
   private static H2CacheImpl<String, String> newH2CacheImpl(
-      int id, Cache<String, ValueHolder<String>> mem, int version) {
-    SqlStore<String, String> store =
-        new SqlStore<>(
-            "jdbc:h2:mem:Test_" + id,
-            KEY_TYPE,
-            StringCacheSerializer.INSTANCE,
-            StringCacheSerializer.INSTANCE,
-            version,
-            1 << 20,
-            null);
+      SqlStore<String, String> store, Cache<String, ValueHolder<String>> mem) {
     return new H2CacheImpl<>(MoreExecutors.directExecutor(), store, KEY_TYPE, mem);
   }
 
+  private static SqlStore<String, String> newStore(
+      int id,
+      int version,
+      @Nullable Duration expireAfterWrite,
+      @Nullable Duration refreshAfterWrite) {
+    return new SqlStore<>(
+        "jdbc:h2:mem:Test_" + id,
+        KEY_TYPE,
+        StringCacheSerializer.INSTANCE,
+        StringCacheSerializer.INSTANCE,
+        version,
+        1 << 20,
+        expireAfterWrite,
+        refreshAfterWrite);
+  }
+
   @Test
   public void get() throws ExecutionException {
     Cache<String, ValueHolder<String>> mem = CacheBuilder.newBuilder().build();
-    H2CacheImpl<String, String> impl = newH2CacheImpl(nextDbId(), mem, DEFAULT_VERSION);
+    H2CacheImpl<String, String> impl =
+        newH2CacheImpl(newStore(nextDbId(), DEFAULT_VERSION, null, null), mem);
 
     assertThat(impl.getIfPresent("foo")).isNull();
 
@@ -94,11 +113,12 @@
   }
 
   @Test
-  public void version() throws Exception {
+  public void version() {
     int id = nextDbId();
-    H2CacheImpl<String, String> oldImpl = newH2CacheImpl(id, disableMemCache(), DEFAULT_VERSION);
+    H2CacheImpl<String, String> oldImpl =
+        newH2CacheImpl(newStore(id, DEFAULT_VERSION, null, null), disableMemCache());
     H2CacheImpl<String, String> newImpl =
-        newH2CacheImpl(id, disableMemCache(), DEFAULT_VERSION + 1);
+        newH2CacheImpl(newStore(id, DEFAULT_VERSION + 1, null, null), disableMemCache());
 
     assertThat(oldImpl.diskStats().space()).isEqualTo(0);
     assertThat(newImpl.diskStats().space()).isEqualTo(0);
@@ -124,6 +144,57 @@
     assertThat(oldImpl.getIfPresent("key")).isNull();
   }
 
+  @Test
+  public void refreshAfterWrite_triggeredWhenConfigured() throws Exception {
+    SqlStore<String, String> store =
+        newStore(nextDbId(), DEFAULT_VERSION, null, Duration.ofMillis(10));
+
+    // This is the loader that we configure for the cache when calling .loader(...)
+    @SuppressWarnings("unchecked")
+    CacheLoader<String, String> baseLoader = (CacheLoader<String, String>) mock(CacheLoader.class);
+    resetLoaderAndAnswerLoadAndRefreshCalls(baseLoader);
+
+    // We wrap baseLoader just like H2CacheFactory is wrapping it. The wrapped version will call out
+    // to the store for refreshing values.
+    H2CacheImpl.Loader<String, String> wrappedLoader =
+        new H2CacheImpl.Loader<>(MoreExecutors.directExecutor(), store, baseLoader);
+    // memCache is the in-memory variant of the cache. Its loader is wrappedLoader which will call
+    // out to the store to save or delete cached values.
+    LoadingCache<String, ValueHolder<String>> memCache =
+        CacheBuilder.newBuilder().maximumSize(10).build(wrappedLoader);
+
+    // h2Cache puts it all together
+    H2CacheImpl<String, String> h2Cache = newH2CacheImpl(store, memCache);
+
+    // Initial load and cache retrieval do not trigger refresh
+    // This works because we use a directExecutor() for refreshes
+    TimeUtil.setCurrentMillisSupplier(() -> 0);
+    assertThat(h2Cache.get("foo")).isEqualTo("load:foo");
+    verify(baseLoader).load("foo");
+    assertThat(h2Cache.get("foo")).isEqualTo("load:foo");
+    verifyNoMoreInteractions(baseLoader);
+    resetLoaderAndAnswerLoadAndRefreshCalls(baseLoader);
+
+    // Load after refresh duration returns old value, triggers refresh and returns new value
+    TimeUtil.setCurrentMillisSupplier(() -> 11);
+    assertThat(h2Cache.get("foo")).isEqualTo("load:foo");
+    assertThat(h2Cache.get("foo")).isEqualTo("reload:foo");
+    verify(baseLoader).reload("foo", "load:foo");
+    verifyNoMoreInteractions(baseLoader);
+    resetLoaderAndAnswerLoadAndRefreshCalls(baseLoader);
+
+    // Refreshed value was persisted
+    memCache.invalidateAll(); // Invalidates only the memcache, not the store.
+    assertThat(h2Cache.getIfPresent("foo")).isEqualTo("reload:foo");
+  }
+
+  private static void resetLoaderAndAnswerLoadAndRefreshCalls(CacheLoader<String, String> loader)
+      throws Exception {
+    reset(loader);
+    when(loader.load("foo")).thenReturn("load:foo");
+    when(loader.reload("foo", "load:foo")).thenReturn(Futures.immediateFuture("reload:foo"));
+  }
+
   private static <K, V> Cache<K, ValueHolder<V>> disableMemCache() {
     return CacheBuilder.newBuilder().maximumSize(0).build();
   }
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item_html.js b/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item_html.js
index b31ab9b..5ff7dde 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item_html.js
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list-item/gr-change-list-item_html.js
@@ -90,10 +90,10 @@
       line-height: var(--line-height-mono);
     }
     .u-green {
-      color: var(--vote-text-color-recommended);
+      color: var(--positive-green-text-color);
     }
     .u-red {
-      color: var(--vote-text-color-disliked);
+      color: var(--negative-red-text-color);
     }
     .u-gray-background {
       background-color: var(--table-header-background-color);
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view_html.js b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view_html.js
index 4add1da..b322f38 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view_html.js
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view_html.js
@@ -86,14 +86,15 @@
         href$="[[_computeNavLink(_query, _offset, -1, _changesPerPage)]]"
         class$="[[_computePrevArrowClass(_offset)]]"
       >
-        <iron-icon icon="gr-icons:chevron-left"></iron-icon>
+        <iron-icon icon="gr-icons:chevron-left" aria-label="Older"> </iron-icon>
       </a>
       <a
         id="nextArrow"
         href$="[[_computeNavLink(_query, _offset, 1, _changesPerPage)]]"
         class$="[[_computeNextArrowClass(_changes)]]"
       >
-        <iron-icon icon="gr-icons:chevron-right"></iron-icon>
+        <iron-icon icon="gr-icons:chevron-right" aria-label="Newer">
+        </iron-icon>
       </a>
     </nav>
   </div>
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.js b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.js
index 916a56f..200ffc9 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.js
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions_html.js
@@ -137,7 +137,6 @@
     <gr-dropdown
       id="moreActions"
       link=""
-      tabindex="0"
       vertical-offset="32"
       horizontal-align="right"
       on-tap-item="_handleOverflowItemTap"
@@ -145,7 +144,8 @@
       disabled-ids="[[_disabledMenuActions]]"
       items="[[_menuActions]]"
     >
-      <iron-icon icon="gr-icons:more-vert"></iron-icon>
+      <iron-icon icon="gr-icons:more-vert" aria-labelledby="moreMessage">
+      </iron-icon>
       <span id="moreMessage">More</span>
     </gr-dropdown>
   </div>
diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.js b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.js
index 1b18412..ca176be 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.js
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_html.js
@@ -74,10 +74,10 @@
       color: #ffa62f;
     }
     .icon.invalid {
-      color: var(--vote-text-color-disliked);
+      color: var(--negative-red-text-color);
     }
     .icon.trusted {
-      color: var(--vote-text-color-recommended);
+      color: var(--positive-green-text-color);
     }
     .parentList.notCurrent.nonMerge #parentNotCurrentMessage {
       --arrow-color: #ffa62f;
diff --git a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.js b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.js
index 0da31de..657915b 100644
--- a/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.js
+++ b/polygerrit-ui/app/elements/change/gr-change-requirements/gr-change-requirements_html.js
@@ -31,10 +31,10 @@
       line-height: var(--line-height-mono);
     }
     .approved.status {
-      color: var(--vote-text-color-recommended);
+      color: var(--positive-green-text-color);
     }
     .rejected.status {
-      color: var(--vote-text-color-disliked);
+      color: var(--negative-red-text-color);
     }
     iron-icon {
       color: inherit;
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
index 05a3ae5..0b29298 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
@@ -2129,7 +2129,8 @@
 
   _handleFileActionTap(e) {
     e.preventDefault();
-    const controls = this.$.fileListHeader.$.editControls;
+    const controls = this.$.fileListHeader
+        .shadowRoot.querySelector('#editControls');
     const path = e.detail.path;
     switch (e.detail.action) {
       case GrEditConstants.Actions.DELETE.id:
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.js b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.js
index 6667ddb..d0b91e2 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.js
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.js
@@ -2000,7 +2000,10 @@
     };
     const fileList = element.$.fileList;
     const Actions = GrEditConstants.Actions;
-    const controls = element.$.fileListHeader.$.editControls;
+    element.$.fileListHeader.editMode = true;
+    flushAsynchronousOperations();
+    const controls = element.$.fileListHeader
+        .shadowRoot.querySelector('#editControls');
     sandbox.stub(controls, 'openDeleteDialog');
     sandbox.stub(controls, 'openRenameDialog');
     sandbox.stub(controls, 'openRestoreDialog');
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.js b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.js
index 10b8606..bb04114 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_html.js
@@ -188,14 +188,16 @@
       </div>
     </div>
     <div class$="rightControls [[_computeExpandedClass(filesExpanded)]]">
-      <span class="showOnEdit flexContainer">
-        <gr-edit-controls
-          id="editControls"
-          patch-num="[[patchNum]]"
-          change="[[change]]"
-        ></gr-edit-controls>
-        <span class="separator"></span>
-      </span>
+      <template is="dom-if" if="[[editMode]]">
+        <span class="showOnEdit flexContainer">
+          <gr-edit-controls
+            id="editControls"
+            patch-num="[[patchNum]]"
+            change="[[change]]"
+          ></gr-edit-controls>
+          <span class="separator"></span>
+        </span>
+      </template>
       <span class$="[[_computeUploadHelpContainerClass(change, account)]]">
         <gr-button link="" class="upload" on-click="_handleUploadTap"
           >Update Change</gr-button
diff --git a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
index 19362d5..2a5a302 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
+++ b/polygerrit-ui/app/elements/change/gr-file-list-header/gr-file-list-header_test.html
@@ -299,13 +299,22 @@
     });
 
     test('edit-controls visibility', () => {
+      element.editMode = false;
+      flushAsynchronousOperations();
+      // on the first render, when editMode is false, editControls are not
+      // in the DOM to reduce size of DOM and make first render faster.
+      assert.isNull(element.shadowRoot
+          .querySelector('#editControls'));
+
       element.editMode = true;
       flushAsynchronousOperations();
-      assert.isTrue(isVisible(element.$.editControls.parentElement));
+      assert.isTrue(isVisible(element.shadowRoot
+          .querySelector('#editControls').parentElement));
 
       element.editMode = false;
       flushAsynchronousOperations();
-      assert.isFalse(isVisible(element.$.editControls.parentElement));
+      assert.isFalse(isVisible(element.shadowRoot
+          .querySelector('#editControls').parentElement));
     });
 
     test('_computeUploadHelpContainerClass', () => {
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
index 12b5aad..d09c942 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list.js
@@ -225,6 +225,11 @@
         computed: '_computeShowDynamicColumns(_dynamicHeaderEndpoints, ' +
                 '_dynamicContentEndpoints, _dynamicSummaryEndpoints)',
       },
+      _showPrependedDynamicColumns: {
+        type: Boolean,
+        computed: '_computeShowPrependedDynamicColumns(' +
+        '_dynamicPrependedHeaderEndpoints, _dynamicPrependedContentEndpoints)',
+      },
       /** @type {Array<string>} */
       _dynamicHeaderEndpoints: {
         type: Array,
@@ -237,6 +242,14 @@
       _dynamicSummaryEndpoints: {
         type: Array,
       },
+      /** @type {Array<string>} */
+      _dynamicPrependedHeaderEndpoints: {
+        type: Array,
+      },
+      /** @type {Array<string>} */
+      _dynamicPrependedContentEndpoints: {
+        type: Array,
+      },
     };
   }
 
@@ -295,18 +308,27 @@
   attached() {
     super.attached();
     pluginLoader.awaitPluginsLoaded().then(() => {
-      this._dynamicHeaderEndpoints = pluginEndpoints.getDynamicEndpoints(
-          'change-view-file-list-header');
-      this._dynamicContentEndpoints = pluginEndpoints.getDynamicEndpoints(
-          'change-view-file-list-content');
-      this._dynamicSummaryEndpoints = pluginEndpoints.getDynamicEndpoints(
-          'change-view-file-list-summary');
+      this._dynamicHeaderEndpoints = pluginEndpoints
+          .getDynamicEndpoints('change-view-file-list-header');
+      this._dynamicContentEndpoints = pluginEndpoints
+          .getDynamicEndpoints('change-view-file-list-content');
+      this._dynamicPrependedHeaderEndpoints = pluginEndpoints
+          .getDynamicEndpoints('change-view-file-list-header-prepend');
+      this._dynamicPrependedContentEndpoints = pluginEndpoints
+          .getDynamicEndpoints('change-view-file-list-content-prepend');
+      this._dynamicSummaryEndpoints = pluginEndpoints
+          .getDynamicEndpoints('change-view-file-list-summary');
 
       if (this._dynamicHeaderEndpoints.length !==
           this._dynamicContentEndpoints.length) {
         console.warn(
             'Different number of dynamic file-list header and content.');
       }
+      if (this._dynamicPrependedHeaderEndpoints.length !==
+        this._dynamicPrependedContentEndpoints.length) {
+        console.warn(
+            'Different number of dynamic file-list header and content.');
+      }
       if (this._dynamicHeaderEndpoints.length !==
           this._dynamicSummaryEndpoints.length) {
         console.warn(
@@ -1432,11 +1454,23 @@
   _computeShowDynamicColumns(
       headerEndpoints, contentEndpoints, summaryEndpoints) {
     return headerEndpoints && contentEndpoints && summaryEndpoints &&
+           headerEndpoints.length &&
            headerEndpoints.length === contentEndpoints.length &&
            headerEndpoints.length === summaryEndpoints.length;
   }
 
   /**
+   * Shows registered dynamic prepended columns iff the 'header', 'content'
+   * endpoints are registered the exact same number of times.
+   */
+  _computeShowPrependedDynamicColumns(
+      headerEndpoints, contentEndpoints) {
+    return headerEndpoints && contentEndpoints &&
+           headerEndpoints.length &&
+           headerEndpoints.length === contentEndpoints.length;
+  }
+
+  /**
    * Returns true if none of the inline diffs have been expanded.
    *
    * @return {boolean}
diff --git a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.js b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.js
index 600b0bc..ccf7f1a 100644
--- a/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.js
+++ b/polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_html.js
@@ -151,10 +151,10 @@
       min-width: 3.5em;
     }
     .added {
-      color: var(--vote-text-color-recommended);
+      color: var(--positive-green-text-color);
     }
     .removed {
-      color: var(--vote-text-color-disliked);
+      color: var(--negative-red-text-color);
       text-align: left;
       min-width: 4em;
       padding-left: var(--spacing-s);
@@ -297,10 +297,22 @@
   </style>
   <div id="container" on-click="_handleFileListClick">
     <div class="header-row row">
+      <!-- endpoint: change-view-file-list-header-prepend -->
+      <template is="dom-if" if="[[_showPrependedDynamicColumns]]">
+        <template
+          is="dom-repeat"
+          items="[[_dynamicPrependedHeaderEndpoints]]"
+          as="headerEndpoint"
+        >
+          <gr-endpoint-decorator name$="[[headerEndpoint]]">
+          </gr-endpoint-decorator>
+        </template>
+      </template>
       <div class="path">File</div>
       <div class="comments">Comments</div>
       <div class="sizeBars">Size</div>
       <div class="header-stats">Delta</div>
+      <!-- endpoint: change-view-file-list-header -->
       <template is="dom-if" if="[[_showDynamicColumns]]">
         <template
           is="dom-repeat"
@@ -332,6 +344,23 @@
           data-file$="[[_computeFileRange(file)]]"
           tabindex="-1"
         >
+          <!-- endpoint: change-view-file-list-content-prepend -->
+          <template is="dom-if" if="[[_showPrependedDynamicColumns]]">
+            <template
+              is="dom-repeat"
+              items="[[_dynamicPrependedContentEndpoints]]"
+              as="contentEndpoint"
+            >
+              <gr-endpoint-decorator name="[[contentEndpoint]]">
+                <gr-endpoint-param name="changeNum" value="[[changeNum]]">
+                </gr-endpoint-param>
+                <gr-endpoint-param name="patchRange" value="[[patchRange]]">
+                </gr-endpoint-param>
+                <gr-endpoint-param name="path" value="[[file.__path]]">
+                </gr-endpoint-param>
+              </gr-endpoint-decorator>
+            </template>
+          </template>
           <!-- TODO: Remove data-url as it appears its not used -->
           <span
             data-url="[[_computeDiffURL(change, patchRange, file.__path, editMode)]]"
@@ -396,14 +425,14 @@
                 x$="[[_computeBarAdditionX(file, _sizeBarLayout)]]"
                 y="0"
                 height="8"
-                fill="#388E3C"
+                fill="var(--positive-green-text-color)"
                 width$="[[_computeBarAdditionWidth(file, _sizeBarLayout)]]"
               ></rect>
               <rect
                 x$="[[_computeBarDeletionX(_sizeBarLayout)]]"
                 y="0"
                 height="8"
-                fill="#D32F2F"
+                fill="var(--negative-red-text-color)"
                 width$="[[_computeBarDeletionWidth(file, _sizeBarLayout)]]"
               ></rect>
             </svg>
@@ -433,6 +462,7 @@
               file.size_delta)]]
             </span>
           </div>
+          <!-- endpoint: change-view-file-list-content -->
           <template is="dom-if" if="[[_showDynamicColumns]]">
             <template
               is="dom-repeat"
@@ -537,6 +567,7 @@
         -[[_patchChange.deleted]]
       </span>
     </div>
+    <!-- endpoint: change-view-file-list-summary -->
     <template is="dom-if" if="[[_showDynamicColumns]]">
       <template
         is="dom-repeat"
diff --git a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog.js b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog.js
index 132cd16..c42c734 100644
--- a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog.js
+++ b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog.js
@@ -74,7 +74,9 @@
   }
 
   _computeGroups(includedIn, filterText) {
-    if (!includedIn) { return []; }
+    if (!includedIn || filterText === undefined) {
+      return [];
+    }
 
     const filter = item => !filterText.length ||
         item.toLowerCase().indexOf(filterText.toLowerCase()) !== -1;
@@ -105,12 +107,6 @@
   _computeLoadingClass(loaded) {
     return loaded ? 'loading loaded' : 'loading';
   }
-
-  _onFilterChanged() {
-    this.debounce('filter-change', () => {
-      this._filterText = this.$.filterInput.bindValue;
-    }, 100);
-  }
 }
 
 customElements.define(GrIncludedInDialog.is, GrIncludedInDialog);
diff --git a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_html.js b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_html.js
index f5948e8..2faac52 100644
--- a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_html.js
+++ b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_html.js
@@ -73,12 +73,15 @@
         >Close</gr-button
       >
     </span>
-    <iron-input placeholder="Filter" on-bind-value-changed="_onFilterChanged">
+    <iron-input
+      id="filterInput"
+      placeholder="Filter"
+      bind-value="{{_filterText}}"
+    >
       <input
-        id="filterInput"
         is="iron-input"
         placeholder="Filter"
-        on-bind-value-changed="_onFilterChanged"
+        bind-value="{{_filterText}}"
       />
     </iron-input>
   </header>
diff --git a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_test.html b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_test.html
index fe6119e..5d5b1fc 100644
--- a/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_test.html
+++ b/polygerrit-ui/app/elements/change/gr-included-in-dialog/gr-included-in-dialog_test.html
@@ -81,5 +81,20 @@
       {title: 'Tags', items: ['v2.0', 'v2.1']},
     ]);
   });
+
+  test('_computeGroups with .bindValue', done => {
+    element.$.filterInput.bindValue = 'stable-3.2';
+    const includedIn = {branches: [], tags: []};
+    includedIn.branches.push('master', 'stable-3.2');
+
+    setTimeout(() => {
+      const filterText = element._filterText;
+      assert.deepEqual(element._computeGroups(includedIn, filterText), [
+        {title: 'Branches', items: ['stable-3.2']},
+      ]);
+
+      done();
+    });
+  });
 });
 </script>
diff --git a/polygerrit-ui/app/elements/change/gr-label-score-row/gr-label-score-row_html.js b/polygerrit-ui/app/elements/change/gr-label-score-row/gr-label-score-row_html.js
index 77148ad..e511101 100644
--- a/polygerrit-ui/app/elements/change/gr-label-score-row/gr-label-score-row_html.js
+++ b/polygerrit-ui/app/elements/change/gr-label-score-row/gr-label-score-row_html.js
@@ -53,7 +53,6 @@
           --button-background-color,
           var(--table-header-background-color)
         );
-        color: var(--primary-text-color);
         padding: 0 var(--spacing-m);
         @apply --vote-chip-styles;
       }
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message.js b/polygerrit-ui/app/elements/change/gr-message/gr-message.js
index b8a405a..8c9d2de 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message.js
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message.js
@@ -74,14 +74,6 @@
         computed: '_computeAuthor(message)',
       },
       /**
-       * Used in cleaner_changelog experiment
-       *
-       * @type {Array} - array of threads attached to the message
-       */
-      commentThreads: {
-        type: Array,
-      },
-      /**
        * TODO(taoalpha): remove once the change log experiment is launched
        *
        * @type {Object} - a map on file and comments on it
@@ -140,11 +132,11 @@
         type: String,
         computed:
             '_computeMessageContentCollapsed(message.message, message.tag,' +
-            ' commentThreads)',
+            ' message.commentThreads)',
       },
       _commentCountText: {
         type: Number,
-        computed: '_computeCommentCountText(comments, commentThreads,'
+        computed: '_computeCommentCountText(comments, message.commentThreads,'
             + ' _isCleanerLogExperimentEnabled)',
       },
       _loggedIn: {
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.js b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.js
index 84713db..25d0f65 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.js
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.js
@@ -132,7 +132,7 @@
     }
     .score {
       border-radius: var(--border-radius);
-      color: var(--primary-text-color);
+      color: var(--vote-text-color);
       display: inline-block;
       padding: 0 var(--spacing-s);
       text-align: center;
@@ -258,8 +258,8 @@
             <template is="dom-if" if="[[_isCleanerLogExperimentEnabled]]">
               <gr-thread-list
                 change="[[change]]"
-                hidden$="[[!commentThreads.length]]"
-                threads="[[commentThreads]]"
+                hidden$="[[!message.commentThreads.length]]"
+                threads="[[message.commentThreads]]"
                 change-num="[[changeNum]]"
                 logged-in="[[_loggedIn]]"
                 hide-toggle-buttons
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental.js b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental.js
index ccc4a76..9037152 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental.js
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental.js
@@ -275,8 +275,9 @@
    * all messages and updates, aligns or massages some of the properties.
    */
   _computeCombinedMessages(messages, reviewerUpdates, changeComments) {
-    messages = messages || [];
-    reviewerUpdates = reviewerUpdates || [];
+    const params = [messages, reviewerUpdates, changeComments];
+    if (params.some(o => o === undefined)) return [];
+
     let mi = 0;
     let ri = 0;
     let combinedMessages = [];
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
index 3fc7ec2..5fd64d2 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_html.js
@@ -113,7 +113,6 @@
     <gr-message
       change-num="[[changeNum]]"
       message="[[message]]"
-      comment-threads="[[message.commentThreads]]"
       project-name="[[projectName]]"
       show-reply-button="[[showReplyButtons]]"
       on-message-anchor-tap="_handleAnchorClick"
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_test.html b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_test.html
index 71f25b7..65229e1 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_test.html
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list-experimental_test.html
@@ -302,11 +302,11 @@
       const messageElements = getMessages();
       // threads
       assert.equal(
-          messageElements[0].commentThreads.length,
+          messageElements[0].message.commentThreads.length,
           3);
       // first thread contains 1 comment
       assert.equal(
-          messageElements[0].commentThreads[0].comments.length,
+          messageElements[0].message.commentThreads[0].comments.length,
           1);
     });
 
diff --git a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.js b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.js
index 687dbd7..6aa7ffc 100644
--- a/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.js
+++ b/polygerrit-ui/app/elements/change/gr-related-changes-list/gr-related-changes-list_html.js
@@ -79,7 +79,7 @@
       color: #1b5e20;
     }
     .submittableCheck {
-      color: var(--vote-text-color-recommended);
+      color: var(--positive-green-text-color);
       display: none;
     }
     .submittableCheck.submittable {
diff --git a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.js b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.js
index 1d4b440..cc11cfa 100644
--- a/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.js
+++ b/polygerrit-ui/app/elements/diff/gr-patch-range-select/gr-patch-range-select_html.js
@@ -51,7 +51,7 @@
       }
     }
   </style>
-  <span class="patchRange">
+  <span class="patchRange" aria-label="patch range starts with">
     <gr-dropdown-list
       id="basePatchDropdown"
       value="[[basePatchNum]]"
@@ -67,8 +67,8 @@
       >
     </template>
   </span>
-  <span class="arrow">→</span>
-  <span class="patchRange">
+  <span aria-hidden="true" class="arrow">→</span>
+  <span class="patchRange" aria-label="patch range ends with">
     <gr-dropdown-list
       id="patchNumDropdown"
       value="[[patchNum]]"
diff --git a/polygerrit-ui/app/elements/shared/gr-button/gr-button.js b/polygerrit-ui/app/elements/shared/gr-button/gr-button.js
index 6ef4807..bdac50f 100644
--- a/polygerrit-ui/app/elements/shared/gr-button/gr-button.js
+++ b/polygerrit-ui/app/elements/shared/gr-button/gr-button.js
@@ -65,6 +65,11 @@
         value: false,
         reflectToAttribute: true,
       },
+      ariaDisabled: {
+        type: Boolean,
+        computed: '_computeDisabled(disabled, loading)',
+        reflectToAttribute: true,
+      },
 
       _disabled: {
         type: Boolean,
diff --git a/polygerrit-ui/app/samples/extra-column-on-file-list.js b/polygerrit-ui/app/samples/extra-column-on-file-list.js
new file mode 100644
index 0000000..2e37c01
--- /dev/null
+++ b/polygerrit-ui/app/samples/extra-column-on-file-list.js
@@ -0,0 +1,77 @@
+/**
+ * @license
+ * Copyright (C) 2020 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.
+ */
+/**
+ * This plugin will an extra column to file list on change page to show
+ * the first character of the path.
+ */
+
+// Header of this extra column
+class ColumnHeader extends Polymer.Element {
+  static get is() { return 'column-header'; }
+
+  static get template() {
+    return Polymer.html`
+      <style>
+      :host {
+        display: block;
+        padding-right: var(--spacing-m);
+        min-width: 5em;
+      }
+      </style>
+      <div>First Char</div>
+    `;
+  }
+}
+
+customElements.define(ColumnHeader.is, ColumnHeader);
+
+// Content of this extra column
+class ColumnContent extends Polymer.Element {
+  static get is() { return 'column-content'; }
+
+  static get properties() {
+    return {
+      path: String,
+    };
+  }
+
+  static get template() {
+    return Polymer.html`
+      <style>
+      :host {
+        display:block;
+        padding-right: var(--spacing-m);
+        min-width: 5em;
+      }
+      </style>
+      <div>[[getStatus(path)]]</div>
+    `;
+  }
+
+  getStatus(path) {
+    return path.charAt(0);
+  }
+}
+
+customElements.define(ColumnContent.is, ColumnContent);
+
+Gerrit.install(plugin => {
+  plugin.registerDynamicCustomComponent(
+      'change-view-file-list-header-prepend', ColumnHeader.is);
+  plugin.registerDynamicCustomComponent(
+      'change-view-file-list-content-prepend', ColumnContent.is);
+});
\ No newline at end of file
diff --git a/polygerrit-ui/app/styles/gr-voting-styles.js b/polygerrit-ui/app/styles/gr-voting-styles.js
index 4860428..60bf623 100644
--- a/polygerrit-ui/app/styles/gr-voting-styles.js
+++ b/polygerrit-ui/app/styles/gr-voting-styles.js
@@ -26,6 +26,7 @@
           box-shadow: none;
           box-sizing: border-box;
           min-width: 3em;
+          color: var(--vote-text-color);
         }
       }
     </style>
diff --git a/polygerrit-ui/app/styles/themes/app-theme.js b/polygerrit-ui/app/styles/themes/app-theme.js
index 5d5d9e3..d76efe1 100644
--- a/polygerrit-ui/app/styles/themes/app-theme.js
+++ b/polygerrit-ui/app/styles/themes/app-theme.js
@@ -38,10 +38,11 @@
   --primary-button-text-color: white;
     /* Used on text color for change list that doesn't need user's attention. */
   --reviewed-text-color: black;
+  --vote-text-color: black;
   --tooltip-text-color: white;
-  --vote-text-color-recommended: #388e3c;
-  --vote-text-color-disliked: #d32f2f;
-
+  --negative-red-text-color: #d93025;
+  --positive-green-text-color: #188038;
+  
   /* background colors */
   /* primary background colors */
   --background-color-primary: #ffffff;
diff --git a/polygerrit-ui/app/styles/themes/dark-theme.html b/polygerrit-ui/app/styles/themes/dark-theme.html
index 4248878..f4cacd2 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.html
+++ b/polygerrit-ui/app/styles/themes/dark-theme.html
@@ -33,12 +33,13 @@
       --deemphasized-text-color: #9aa0a6;
       --default-button-text-color: #8ab4f8;
       --error-text-color: red;
-      --primary-button-text-color: var(--primary-text-color);
+      --primary-button-text-color: black;
         /* Used on text color for change list doesn't need user's attention. */
       --reviewed-text-color: #dadce0;
+      --vote-text-color: black;
       --tooltip-text-color: white;
-      --vote-text-color-recommended: #388e3c;
-      --vote-text-color-disliked: #d32f2f;
+      --negative-red-text-color: #f28b82;
+      --positive-green-text-color: #81c995;
 
       /* background colors */
       /* primary background colors */
diff --git a/polygerrit-ui/server.go b/polygerrit-ui/server.go
index 120aff5..c44493d 100644
--- a/polygerrit-ui/server.go
+++ b/polygerrit-ui/server.go
@@ -61,6 +61,7 @@
 
 	dirListingMux := http.NewServeMux()
 	dirListingMux.Handle("/styles/", http.StripPrefix("/styles/", http.FileServer(http.Dir("app/styles"))))
+	dirListingMux.Handle("/samples/", http.StripPrefix("/samples/", http.FileServer(http.Dir("app/samples"))))
 	dirListingMux.Handle("/elements/", http.StripPrefix("/elements/", http.FileServer(http.Dir("app/elements"))))
 	dirListingMux.Handle("/behaviors/", http.StripPrefix("/behaviors/", http.FileServer(http.Dir("app/behaviors"))))