Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.9 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.8 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.18 API
  ForwardedIndexChangeHandler: Replace parameter writing with variable
  PeerInfoNotAvailableException: Remove this class as no longer used
  Forwarder tests: Convert useless members to local variable
  ForwardedIndexChangeHandlerTest: Remove unused gitRepoMgrMock
  ChangeChecker{Impl}: Remove redundant public modifier
  ForwardedIndexChangeHandler: Remove redundant local variable
  ChangeReindexRunnable: Replace statement lambda with expression
  IndexTs: Move local variable to used scope
  ForwardedIndexChangeHandler: Remove unused changeFinder parameter
  Catch all exceptions when indexTs fails
  Minimize use of ReviewDb when not needed
  Retry change reindex because of NFS access caching
  RestForwarder: Replace lambda with method reference
  Always use the stored timestamp when checking for updates
  Use always the last TS of the reindex across runs
  GroupReindexRunnable: Replace lambdas with method reference
  Support n nodes when using static strategy

Change-Id: Ifcc5dd45444df869026434323c31f139bcd56e51
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/Configuration.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/Configuration.java
index 8f1963a..edd96d7 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/Configuration.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/Configuration.java
@@ -20,6 +20,7 @@
 import com.google.common.base.CharMatcher;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.extensions.annotations.PluginName;
 import com.google.gerrit.server.config.ConfigUtil;
@@ -32,8 +33,11 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
 import org.eclipse.jgit.lib.Config;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -47,6 +51,8 @@
 
   // common parameters to cache and index sections
   static final String THREAD_POOL_SIZE_KEY = "threadPoolSize";
+  static final int DEFAULT_INDEX_MAX_TRIES = 2;
+  static final int DEFAULT_INDEX_RETRY_INTERVAL = 30000;
   static final int DEFAULT_THREAD_POOL_SIZE = 4;
   static final String NUM_STRIPED_LOCKS = "numStripedLocks";
   static final int DEFAULT_NUM_STRIPED_LOCKS = 10;
@@ -153,11 +159,6 @@
     }
   }
 
-  @Nullable
-  private static String trimTrailingSlash(@Nullable String in) {
-    return in == null ? null : CharMatcher.is('/').trimTrailingFrom(in);
-  }
-
   public static class Main {
     static final String MAIN_SECTION = "main";
     static final String SHARED_DIRECTORY_KEY = "sharedDirectory";
@@ -247,17 +248,20 @@
     static final String STATIC_SUBSECTION = PeerInfoStrategy.STATIC.name().toLowerCase();
     static final String URL_KEY = "url";
 
-    private final String url;
+    private final Set<String> urls;
 
     private PeerInfoStatic(Config cfg) {
-      url =
-          trimTrailingSlash(
-              Strings.nullToEmpty(cfg.getString(PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY)));
-      log.debug("Url: {}", url);
+      urls =
+          Arrays.stream(cfg.getStringList(PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY))
+              .filter(Objects::nonNull)
+              .filter(s -> !s.isEmpty())
+              .map(s -> CharMatcher.is('/').trimTrailingFrom(s))
+              .collect(Collectors.toSet());
+      log.debug("Urls: {}", urls);
     }
 
-    public String url() {
-      return url;
+    public Set<String> urls() {
+      return ImmutableSet.copyOf(urls);
     }
   }
 
@@ -275,6 +279,11 @@
     public String myUrl() {
       return myUrl;
     }
+
+    @Nullable
+    private static String trimTrailingSlash(@Nullable String in) {
+      return in == null ? in : CharMatcher.is('/').trimTrailingFrom(in);
+    }
   }
 
   public static class JGroups {
@@ -439,8 +448,12 @@
 
   public static class Index extends Forwarding {
     static final String INDEX_SECTION = "index";
+    static final String MAX_TRIES_KEY = "maxTries";
+    static final String RETRY_INTERVAL_KEY = "retryInterval";
 
     private final int threadPoolSize;
+    private final int retryInterval;
+    private final int maxTries;
 
     private final int numStripedLocks;
 
@@ -448,6 +461,8 @@
       super(cfg, INDEX_SECTION);
       threadPoolSize = getInt(cfg, INDEX_SECTION, THREAD_POOL_SIZE_KEY, DEFAULT_THREAD_POOL_SIZE);
       numStripedLocks = getInt(cfg, INDEX_SECTION, NUM_STRIPED_LOCKS, DEFAULT_NUM_STRIPED_LOCKS);
+      retryInterval = getInt(cfg, INDEX_SECTION, RETRY_INTERVAL_KEY, DEFAULT_INDEX_RETRY_INTERVAL);
+      maxTries = getInt(cfg, INDEX_SECTION, MAX_TRIES_KEY, DEFAULT_INDEX_MAX_TRIES);
     }
 
     public int threadPoolSize() {
@@ -457,6 +472,14 @@
     public int numStripedLocks() {
       return numStripedLocks;
     }
+
+    public int retryInterval() {
+      return retryInterval;
+    }
+
+    public int maxTries() {
+      return maxTries;
+    }
   }
 
   public static class Websession extends Forwarding {
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
index 597034d..3d3212b 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
@@ -17,11 +17,11 @@
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.inject.Provider;
-import java.util.concurrent.Executor;
-import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ScheduledExecutorService;
 
-public abstract class ExecutorProvider implements Provider<Executor>, LifecycleListener {
-  private ExecutorService executor;
+public abstract class ExecutorProvider
+    implements Provider<ScheduledExecutorService>, LifecycleListener {
+  private ScheduledExecutorService executor;
 
   protected ExecutorProvider(WorkQueue workQueue, int threadPoolSize, String threadNamePrefix) {
     executor = workQueue.createQueue(threadPoolSize, threadNamePrefix);
@@ -39,7 +39,7 @@
   }
 
   @Override
-  public Executor get() {
+  public ScheduledExecutorService get() {
     return executor;
   }
 }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/Setup.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/Setup.java
index e58f62f..86c757e 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/Setup.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/Setup.java
@@ -164,7 +164,8 @@
             PeerInfoStrategy.JGROUPS, EnumSet.allOf(PeerInfoStrategy.class), "Peer info strategy");
     config.setEnum(PEER_INFO_SECTION, null, STRATEGY_KEY, strategy);
     if (strategy == PeerInfoStrategy.STATIC) {
-      promptAndSetString("Peer URL", PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY, null);
+      promptAndSetString(
+          titleWithNote("Peer URL", "urls"), PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY, null);
     } else {
       promptAndSetString(
           "JGroups cluster name",
@@ -291,7 +292,11 @@
   }
 
   private static String titleForOptionalWithNote(String prefix, String suffix) {
-    return prefix + " (optional); manually repeat this line to configure more " + suffix;
+    return titleWithNote(prefix + " (optional)", suffix);
+  }
+
+  private static String titleWithNote(String prefix, String suffix) {
+    return prefix + "; manually repeat this line to configure more " + suffix;
   }
 
   private static String numberToString(int number) {
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ChangeReindexRunnable.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ChangeReindexRunnable.java
index 62a9792..1f5b56e 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ChangeReindexRunnable.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ChangeReindexRunnable.java
@@ -86,10 +86,7 @@
         Stream<Change> projectChangesStream =
             notesFactory
                 .scan(repo, db, projectName)
-                .map(
-                    (ChangeNotesResult changeNotes) -> {
-                      return changeNotes.notes().getChange();
-                    });
+                .map((ChangeNotesResult changeNotes) -> changeNotes.notes().getChange());
         allChangesStream = Streams.concat(allChangesStream, projectChangesStream);
       }
     }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/IndexTs.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/IndexTs.java
index 40b4117..6b13bb1 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/IndexTs.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/IndexTs.java
@@ -24,7 +24,6 @@
 import com.google.gerrit.server.change.ChangeFinder;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.notedb.ChangeNotes;
-import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
@@ -34,8 +33,6 @@
 import java.nio.file.Path;
 import java.time.LocalDateTime;
 import java.time.format.DateTimeFormatter;
-import java.util.HashMap;
-import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.ScheduledExecutorService;
 import org.slf4j.Logger;
@@ -58,7 +55,6 @@
   private volatile LocalDateTime groupTs;
 
   class FlusherRunner implements Runnable {
-    private Map<AbstractIndexRestApiServlet.IndexName, LocalDateTime> storedTs = new HashMap<>();
 
     @Override
     public void run() {
@@ -68,12 +64,11 @@
     }
 
     private void store(AbstractIndexRestApiServlet.IndexName index, LocalDateTime latestTs) {
-      LocalDateTime currTs = storedTs.get(index);
-      if (currTs == null || latestTs.isAfter(currTs)) {
+      Optional<LocalDateTime> currTs = getUpdateTs(index);
+      if (!currTs.isPresent() || latestTs.isAfter(currTs.get())) {
         Path indexTsFile = dataDir.resolve(index.name().toLowerCase());
         try {
           Files.write(indexTsFile, latestTs.format(formatter).getBytes(StandardCharsets.UTF_8));
-          storedTs.put(index, currTs);
         } catch (IOException e) {
           log.error("Unable to update last timestamp for index " + index, e);
         }
@@ -113,7 +108,7 @@
           changeNotes == null
               ? LocalDateTime.now()
               : changeNotes.getChange().getLastUpdatedOn().toLocalDateTime());
-    } catch (OrmException e) {
+    } catch (Exception e) {
       log.warn("Unable to update the latest TS for change {}", e);
     }
   }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ReindexRunnable.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ReindexRunnable.java
index 7891bbf..df3a0fd 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ReindexRunnable.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/autoreindex/ReindexRunnable.java
@@ -33,6 +33,7 @@
   private final AbstractIndexRestApiServlet.IndexName itemName;
   private final OneOffRequestContext ctx;
   private final IndexTs indexTs;
+  private Timestamp newLastIndexTs;
 
   @Inject
   public ReindexRunnable(
@@ -47,9 +48,8 @@
     Optional<LocalDateTime> maybeIndexTs = indexTs.getUpdateTs(itemName);
     String itemNameString = itemName.name().toLowerCase();
     if (maybeIndexTs.isPresent()) {
-      Timestamp lastIndexTs = Timestamp.valueOf(maybeIndexTs.get());
-      Timestamp newLastIndexTs = lastIndexTs;
-      log.debug("Scanning for all the {}s after {}", itemNameString, lastIndexTs);
+      newLastIndexTs = maxTimestamp(newLastIndexTs, Timestamp.valueOf(maybeIndexTs.get()));
+      log.debug("Scanning for all the {}s after {}", itemNameString, newLastIndexTs);
       try (ManualRequestContext mctx = ctx.open();
           ReviewDb db = mctx.getReviewDbProvider().get()) {
         int count = 0;
@@ -57,12 +57,10 @@
         Stopwatch stopwatch = Stopwatch.createStarted();
         for (T c : fetchItems(db)) {
           try {
-            Optional<Timestamp> itemTs = indexIfNeeded(db, c, lastIndexTs);
+            Optional<Timestamp> itemTs = indexIfNeeded(db, c, newLastIndexTs);
             if (itemTs.isPresent()) {
               count++;
-              if (itemTs.get().after(newLastIndexTs)) {
-                newLastIndexTs = itemTs.get();
-              }
+              newLastIndexTs = maxTimestamp(newLastIndexTs, itemTs.get());
             }
           } catch (Exception e) {
             log.error("Unable to reindex {} {}", itemNameString, c, e);
@@ -90,6 +88,21 @@
     }
   }
 
+  private Timestamp maxTimestamp(Timestamp ts1, Timestamp ts2) {
+    if (ts1 == null) {
+      return ts2;
+    }
+
+    if (ts2 == null) {
+      return ts1;
+    }
+
+    if (ts1.after(ts2)) {
+      return ts1;
+    }
+    return ts2;
+  }
+
   protected abstract Iterable<T> fetchItems(ReviewDb db) throws Exception;
 
   protected abstract Optional<Timestamp> indexIfNeeded(ReviewDb db, T item, Timestamp sinceTs);
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandler.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandler.java
index eb738d9..d34959c 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandler.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandler.java
@@ -15,19 +15,26 @@
 package com.ericsson.gerrit.plugins.highavailability.forwarder;
 
 import com.ericsson.gerrit.plugins.highavailability.Configuration;
+import com.ericsson.gerrit.plugins.highavailability.Configuration.Index;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeChecker;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeCheckerImpl;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeDb;
+import com.ericsson.gerrit.plugins.highavailability.index.ForwardedIndexExecutor;
 import com.google.common.base.Splitter;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.server.ReviewDb;
-import com.google.gerrit.server.change.ChangeFinder;
 import com.google.gerrit.server.index.change.ChangeIndexer;
 import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.project.NoSuchChangeException;
+import com.google.gerrit.server.util.ManualRequestContext;
+import com.google.gerrit.server.util.OneOffRequestContext;
 import com.google.gwtorm.server.OrmException;
-import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import java.io.IOException;
 import java.util.Optional;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Index a change using {@link ChangeIndexer}. This class is meant to be used on the receiving side
@@ -38,44 +45,114 @@
 @Singleton
 public class ForwardedIndexChangeHandler extends ForwardedIndexingHandler<String> {
   private final ChangeIndexer indexer;
-  private final SchemaFactory<ReviewDb> schemaFactory;
-  private final ChangeFinder changeFinder;
+  private final ChangeDb changeDb;
+  private final ScheduledExecutorService indexExecutor;
+  private final OneOffRequestContext oneOffCtx;
+  private final int retryInterval;
+  private final int maxTries;
+  private final ChangeCheckerImpl.Factory changeCheckerFactory;
 
   @Inject
   ForwardedIndexChangeHandler(
       ChangeIndexer indexer,
-      SchemaFactory<ReviewDb> schemaFactory,
-      ChangeFinder changeFinder,
-      Configuration config) {
+      ChangeDb changeDb,
+      Configuration config,
+      @ForwardedIndexExecutor ScheduledExecutorService indexExecutor,
+      OneOffRequestContext oneOffCtx,
+      ChangeCheckerImpl.Factory changeCheckerFactory) {
     super(config.index());
     this.indexer = indexer;
-    this.schemaFactory = schemaFactory;
-    this.changeFinder = changeFinder;
+    this.changeDb = changeDb;
+    this.indexExecutor = indexExecutor;
+    this.oneOffCtx = oneOffCtx;
+    this.changeCheckerFactory = changeCheckerFactory;
+
+    Index indexConfig = config.index();
+    this.retryInterval = indexConfig != null ? indexConfig.retryInterval() : 0;
+    this.maxTries = indexConfig != null ? indexConfig.maxTries() : 0;
   }
 
   @Override
   protected void doIndex(String id, Optional<IndexEvent> indexEvent)
       throws IOException, OrmException {
-    ChangeNotes change = null;
-    try (ReviewDb db = schemaFactory.open()) {
-      change = changeFinder.findOne(id);
-      if (change != null) {
-        change.reload();
-        indexer.index(db, change.getChange());
-        log.debug("Change {} successfully indexed", id);
+    doIndex(id, indexEvent, 0);
+  }
+
+  private void doIndex(String id, Optional<IndexEvent> indexEvent, int retryCount)
+      throws IOException, OrmException {
+    try {
+      ChangeChecker checker = changeCheckerFactory.create(id);
+      Optional<ChangeNotes> changeNotes = checker.getChangeNotes();
+      if (changeNotes.isPresent()) {
+        ChangeNotes notes = changeNotes.get();
+        reindex(notes);
+
+        if (checker.isChangeUpToDate(indexEvent)) {
+          if (retryCount > 0) {
+            log.warn("Change {} has been eventually indexed after {} attempt(s)", id, retryCount);
+          } else {
+            log.debug("Change {} successfully indexed", id);
+          }
+        } else {
+          log.warn(
+              "Change {} seems too old compared to the event timestamp (event-Ts={} >> change-Ts={})",
+              id,
+              indexEvent,
+              checker);
+          rescheduleIndex(id, indexEvent, retryCount + 1);
+        }
+      } else {
+        indexer.delete(parseChangeId(id));
+        log.warn(
+            "Change {} could not be found in the local Git repository (eventTs={}), deleted from index",
+            id,
+            indexEvent);
       }
     } catch (Exception e) {
-      if (!isCausedByNoSuchChangeException(e)) {
-        throw e;
+      if (isCausedByNoSuchChangeException(e)) {
+        indexer.delete(parseChangeId(id));
+        log.warn("Error trying to index Change {}. Deleted from index", id, e);
+        return;
       }
-      log.debug("Change {} was deleted, aborting forwarded indexing the change.", id);
+
+      throw e;
     }
-    if (change == null) {
-      indexer.delete(parseChangeId(id));
-      log.debug("Change {} not found, deleted from index", id);
+  }
+
+  private void reindex(ChangeNotes notes) throws IOException, OrmException {
+    try (ReviewDb db = changeDb.open()) {
+      notes.reload();
+      indexer.index(db, notes.getChange());
     }
   }
 
+  private void rescheduleIndex(String id, Optional<IndexEvent> indexEvent, int retryCount) {
+    if (retryCount > maxTries) {
+      log.error(
+          "Change {} could not be indexed after {} retries. Change index could be stale.",
+          id,
+          retryCount);
+      return;
+    }
+
+    log.warn(
+        "Retrying for the #{} time to index Change {} after {} msecs",
+        retryCount,
+        id,
+        retryInterval);
+    indexExecutor.schedule(
+        () -> {
+          try (ManualRequestContext ctx = oneOffCtx.open()) {
+            Context.setForwardedEvent(true);
+            doIndex(id, indexEvent, retryCount);
+          } catch (Exception e) {
+            log.warn("Change {} could not be indexed", id, e);
+          }
+        },
+        retryInterval,
+        TimeUnit.MILLISECONDS);
+  }
+
   @Override
   protected void doDelete(String id, Optional<IndexEvent> indexEvent) throws IOException {
     indexer.delete(parseChangeId(id));
@@ -83,16 +160,16 @@
   }
 
   private static Change.Id parseChangeId(String id) {
-    Change.Id changeId = new Change.Id(Integer.parseInt(Splitter.on("~").splitToList(id).get(1)));
-    return changeId;
+    return new Change.Id(Integer.parseInt(Splitter.on("~").splitToList(id).get(1)));
   }
 
   private static boolean isCausedByNoSuchChangeException(Throwable throwable) {
-    while (throwable != null) {
-      if (throwable instanceof NoSuchChangeException) {
+    Throwable cause = throwable;
+    while (cause != null) {
+      if (cause instanceof NoSuchChangeException) {
         return true;
       }
-      throwable = throwable.getCause();
+      cause = cause.getCause();
     }
     return false;
   }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/IndexEvent.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/IndexEvent.java
index f6f24a7..037c1c6 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/IndexEvent.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/IndexEvent.java
@@ -20,11 +20,15 @@
 
 public class IndexEvent {
   public long eventCreatedOn = System.currentTimeMillis() / 1000;
+  public String targetSha;
 
   @Override
   public String toString() {
-    return "IndexEvent@"
-        + LocalDateTime.ofEpochSecond(eventCreatedOn, 0, ZoneOffset.UTC)
-            .format(DateTimeFormatter.ISO_DATE_TIME);
+    return "IndexEvent@" + format(eventCreatedOn) + ((targetSha != null) ? "/" + targetSha : "");
+  }
+
+  public static String format(long eventTs) {
+    return LocalDateTime.ofEpochSecond(eventTs, 0, ZoneOffset.UTC)
+        .format(DateTimeFormatter.ISO_DATE_TIME);
   }
 }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSession.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSession.java
index 253dca7..f2ac080 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSession.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSession.java
@@ -15,18 +15,15 @@
 package com.ericsson.gerrit.plugins.highavailability.forwarder.rest;
 
 import com.ericsson.gerrit.plugins.highavailability.forwarder.rest.HttpResponseHandler.HttpResult;
-import com.ericsson.gerrit.plugins.highavailability.peers.PeerInfo;
 import com.google.common.base.Supplier;
 import com.google.common.net.MediaType;
 import com.google.gerrit.server.events.SupplierSerializer;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.inject.Inject;
-import com.google.inject.Provider;
 import java.io.IOException;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
-import java.util.Optional;
 import org.apache.http.client.methods.HttpDelete;
 import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;
 import org.apache.http.client.methods.HttpPost;
@@ -35,40 +32,30 @@
 
 class HttpSession {
   private final CloseableHttpClient httpClient;
-  private final Provider<Optional<PeerInfo>> peerInfo;
   private final Gson gson =
       new GsonBuilder().registerTypeAdapter(Supplier.class, new SupplierSerializer()).create();
 
   @Inject
-  HttpSession(CloseableHttpClient httpClient, Provider<Optional<PeerInfo>> peerInfo) {
+  HttpSession(CloseableHttpClient httpClient) {
     this.httpClient = httpClient;
-    this.peerInfo = peerInfo;
   }
 
-  HttpResult post(String endpoint) throws IOException {
-    return post(endpoint, null);
+  HttpResult post(String uri) throws IOException {
+    return post(uri, null);
   }
 
-  HttpResult post(String endpoint, Object content) throws IOException {
-    HttpPost post = new HttpPost(getPeerInfo().getDirectUrl() + endpoint);
+  HttpResult post(String uri, Object content) throws IOException {
+    HttpPost post = new HttpPost(uri);
     setContent(post, content);
     return httpClient.execute(post, new HttpResponseHandler());
   }
 
-  HttpResult delete(String endpoint) throws IOException {
-    return delete(endpoint, null);
+  HttpResult delete(String uri) throws IOException {
+    return delete(uri, null);
   }
 
-  private PeerInfo getPeerInfo() throws PeerInfoNotAvailableException {
-    PeerInfo info = peerInfo.get().orElse(null);
-    if (info == null) {
-      throw new PeerInfoNotAvailableException();
-    }
-    return info;
-  }
-
-  HttpResult delete(String endpoint, Object content) throws IOException {
-    HttpDeleteWithBody delete = new HttpDeleteWithBody(getPeerInfo().getDirectUrl() + endpoint);
+  HttpResult delete(String uri, Object content) throws IOException {
+    HttpDeleteWithBody delete = new HttpDeleteWithBody(uri);
     setContent(delete, content);
     return httpClient.execute(delete, new HttpResponseHandler());
   }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarder.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarder.java
index 1e9e931..ab7b81a 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarder.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarder.java
@@ -19,12 +19,18 @@
 import com.ericsson.gerrit.plugins.highavailability.forwarder.Forwarder;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.IndexEvent;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.rest.HttpResponseHandler.HttpResult;
+import com.ericsson.gerrit.plugins.highavailability.peers.PeerInfo;
 import com.google.common.base.Joiner;
 import com.google.gerrit.extensions.annotations.PluginName;
 import com.google.gerrit.extensions.restapi.Url;
 import com.google.gerrit.server.events.Event;
 import com.google.inject.Inject;
+import com.google.inject.Provider;
 import java.io.IOException;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.stream.Collectors;
 import javax.net.ssl.SSLException;
 import org.apache.http.HttpException;
 import org.apache.http.client.ClientProtocolException;
@@ -32,59 +38,54 @@
 import org.slf4j.LoggerFactory;
 
 class RestForwarder implements Forwarder {
+  enum RequestMethod {
+    POST,
+    DELETE
+  }
+
   private static final Logger log = LoggerFactory.getLogger(RestForwarder.class);
 
   private final HttpSession httpSession;
   private final String pluginRelativePath;
   private final Configuration cfg;
+  private final Provider<Set<PeerInfo>> peerInfoProvider;
 
   @Inject
-  RestForwarder(HttpSession httpClient, @PluginName String pluginName, Configuration cfg) {
+  RestForwarder(
+      HttpSession httpClient,
+      @PluginName String pluginName,
+      Configuration cfg,
+      Provider<Set<PeerInfo>> peerInfoProvider) {
     this.httpSession = httpClient;
-    this.pluginRelativePath = Joiner.on("/").join("/plugins", pluginName);
+    this.pluginRelativePath = Joiner.on("/").join("plugins", pluginName);
     this.cfg = cfg;
+    this.peerInfoProvider = peerInfoProvider;
   }
 
   @Override
   public boolean indexAccount(final int accountId, IndexEvent event) {
-    return new Request("index account", accountId) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.post(
-            Joiner.on("/").join(pluginRelativePath, "index/account", accountId), event);
-      }
-    }.execute();
+    return execute(RequestMethod.POST, "index account", "index/account", accountId, event);
   }
 
   @Override
   public boolean indexChange(String projectName, int changeId, IndexEvent event) {
-    return new Request("index change", changeId) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.post(buildIndexEndpoint(projectName, changeId), event);
-      }
-    }.execute();
+    return execute(
+        RequestMethod.POST,
+        "index change",
+        "index/change",
+        buildIndexEndpoint(projectName, changeId),
+        event);
   }
 
   @Override
   public boolean deleteChangeFromIndex(final int changeId, IndexEvent event) {
-    return new Request("delete change", changeId) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.delete(buildIndexEndpoint(changeId), event);
-      }
-    }.execute();
+    return execute(
+        RequestMethod.DELETE, "delete change", "index/change", buildIndexEndpoint(changeId), event);
   }
 
   @Override
   public boolean indexGroup(final String uuid, IndexEvent event) {
-    return new Request("index group", uuid) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.post(
-            Joiner.on("/").join(pluginRelativePath, "index/group", uuid), event);
-      }
-    }.execute();
+    return execute(RequestMethod.POST, "index group", "index/group", uuid, event);
   }
 
   private String buildIndexEndpoint(int changeId) {
@@ -93,91 +94,131 @@
 
   private String buildIndexEndpoint(String projectName, int changeId) {
     String escapedProjectName = Url.encode(projectName);
-    return Joiner.on("/")
-        .join(pluginRelativePath, "index/change", escapedProjectName + '~' + changeId);
+    return escapedProjectName + '~' + changeId;
   }
 
   @Override
   public boolean send(final Event event) {
-    return new Request("send event", event.type) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.post(Joiner.on("/").join(pluginRelativePath, "event"), event);
-      }
-    }.execute();
+    return execute(RequestMethod.POST, "send event", "event", event.type, event);
   }
 
   @Override
   public boolean evict(final String cacheName, final Object key) {
-    return new Request("invalidate cache " + cacheName, key) {
-      @Override
-      HttpResult send() throws IOException {
-        String json = GsonParser.toJson(cacheName, key);
-        return httpSession.post(Joiner.on("/").join(pluginRelativePath, "cache", cacheName), json);
-      }
-    }.execute();
+    String json = GsonParser.toJson(cacheName, key);
+    return execute(RequestMethod.POST, "invalidate cache " + cacheName, "cache", cacheName, json);
   }
 
   @Override
   public boolean addToProjectList(String projectName) {
-    return new Request("Update project_list, add ", projectName) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.post(buildProjectListEndpoint(projectName));
-      }
-    }.execute();
+    return execute(
+        RequestMethod.POST,
+        "Update project_list, add ",
+        buildProjectListEndpoint(),
+        Url.encode(projectName));
   }
 
   @Override
   public boolean removeFromProjectList(String projectName) {
-    return new Request("Update project_list, remove ", projectName) {
-      @Override
-      HttpResult send() throws IOException {
-        return httpSession.delete(buildProjectListEndpoint(projectName));
-      }
-    }.execute();
+    return execute(
+        RequestMethod.DELETE,
+        "Update project_list, remove ",
+        buildProjectListEndpoint(),
+        Url.encode(projectName));
   }
 
-  private String buildProjectListEndpoint(String projectName) {
-    return Joiner.on("/")
-        .join(pluginRelativePath, "cache", Constants.PROJECT_LIST, Url.encode(projectName));
+  private static String buildProjectListEndpoint() {
+    return Joiner.on("/").join("cache", Constants.PROJECT_LIST);
+  }
+
+  private boolean execute(RequestMethod method, String action, String endpoint, Object id) {
+    return execute(method, action, endpoint, id, null);
+  }
+
+  private boolean execute(
+      RequestMethod method, String action, String endpoint, Object id, Object payload) {
+    List<CompletableFuture<Boolean>> futures =
+        peerInfoProvider
+            .get()
+            .stream()
+            .map(peer -> createRequest(method, peer, action, endpoint, id, payload))
+            .map(request -> CompletableFuture.supplyAsync(request::execute))
+            .collect(Collectors.toList());
+    CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).join();
+    return futures.stream().allMatch(CompletableFuture::join);
+  }
+
+  private Request createRequest(
+      RequestMethod method,
+      PeerInfo peer,
+      String action,
+      String endpoint,
+      Object id,
+      Object payload) {
+    String destination = peer.getDirectUrl();
+    return new Request(action, id, destination) {
+      @Override
+      HttpResult send() throws IOException {
+        String request = Joiner.on("/").join(destination, pluginRelativePath, endpoint, id);
+        switch (method) {
+          case POST:
+            return httpSession.post(request, payload);
+          case DELETE:
+          default:
+            return httpSession.delete(request);
+        }
+      }
+    };
   }
 
   private abstract class Request {
     private final String action;
     private final Object key;
+    private final String destination;
+
     private int execCnt;
 
-    Request(String action, Object key) {
+    Request(String action, Object key, String destination) {
       this.action = action;
       this.key = key;
+      this.destination = destination;
     }
 
     boolean execute() {
-      log.debug("Executing {} {}", action, key);
+      log.debug("Executing {} {} towards {}", action, key, destination);
       for (; ; ) {
         try {
           execCnt++;
           tryOnce();
-          log.debug("{} {} OK", action, key);
+          log.debug("{} {} towards {} OK", action, key, destination);
           return true;
         } catch (ForwardingException e) {
           int maxTries = cfg.http().maxTries();
-          log.debug("Failed to {} {} [{}/{}]", action, key, execCnt, maxTries, e);
+          log.debug(
+              "Failed to {} {} on {} [{}/{}]", action, key, destination, execCnt, maxTries, e);
           if (!e.isRecoverable()) {
-            log.error("{} {} failed with unrecoverable error; giving up", action, key, e);
+            log.error(
+                "{} {} towards {} failed with unrecoverable error; giving up",
+                action,
+                key,
+                destination,
+                e);
             return false;
           }
           if (execCnt >= maxTries) {
-            log.error("Failed to {} {} after {} tries; giving up", action, key, maxTries);
+            log.error(
+                "Failed to {} {} on {} after {} tries; giving up",
+                action,
+                key,
+                destination,
+                maxTries);
             return false;
           }
 
-          log.debug("Retrying to {} {}", action, key);
+          log.debug("Retrying to {} {} on {}", action, key, destination);
           try {
             Thread.sleep(cfg.http().retryInterval());
           } catch (InterruptedException ie) {
-            log.error("{} {} was interrupted; giving up", action, key, ie);
+            log.error("{} {} towards {} was interrupted; giving up", action, key, destination, ie);
             Thread.currentThread().interrupt();
             return false;
           }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeChecker.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeChecker.java
new file mode 100644
index 0000000..ce04589
--- /dev/null
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeChecker.java
@@ -0,0 +1,63 @@
+// Copyright (C) 2018 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.ericsson.gerrit.plugins.highavailability.index;
+
+import com.ericsson.gerrit.plugins.highavailability.forwarder.IndexEvent;
+import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gwtorm.server.OrmException;
+import java.io.IOException;
+import java.util.Optional;
+
+/** Encapsulates the logic of verifying the up-to-date status of a change. */
+public interface ChangeChecker {
+
+  /**
+   * Return the Change notes read from ReviewDb or NoteDb.
+   *
+   * @return notes of the Change
+   * @throws OrmException if ReviewDb or NoteDb cannot be opened
+   */
+  Optional<ChangeNotes> getChangeNotes() throws OrmException;
+
+  /**
+   * Create a new index event POJO associated with the current Change.
+   *
+   * @return new IndexEvent
+   * @throws IOException if the current Change cannot read
+   * @throws OrmException if ReviewDb cannot be opened
+   */
+  Optional<IndexEvent> newIndexEvent() throws IOException, OrmException;
+
+  /**
+   * Check if the local Change is aligned with the indexEvent received.
+   *
+   * @param indexEvent indexing event
+   * @return true if the local Change is up-to-date, false otherwise.
+   * @throws IOException if an I/O error occurred while reading the local Change
+   * @throws OrmException if the local ReviewDb cannot be opened
+   */
+  boolean isChangeUpToDate(Optional<IndexEvent> indexEvent) throws IOException, OrmException;
+
+  /**
+   * Return the last computed up-to-date Change time-stamp.
+   *
+   * <p>Compute the up-to-date Change time-stamp when it is invoked for the very first time.
+   *
+   * @return the Change timestamp epoch in seconds
+   * @throws IOException if an I/O error occurred while reading the local Change
+   * @throws OrmException if the local ReviewDb cannot be opened
+   */
+  Optional<Long> getComputedChangeTs() throws IOException, OrmException;
+}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeCheckerImpl.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeCheckerImpl.java
new file mode 100644
index 0000000..75f3086
--- /dev/null
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeCheckerImpl.java
@@ -0,0 +1,170 @@
+// Copyright (C) 2018 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.ericsson.gerrit.plugins.highavailability.index;
+
+import com.ericsson.gerrit.plugins.highavailability.forwarder.IndexEvent;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Comment;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.CommentsUtil;
+import com.google.gerrit.server.change.ChangeFinder;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.util.ManualRequestContext;
+import com.google.gerrit.server.util.OneOffRequestContext;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.assistedinject.Assisted;
+import java.io.IOException;
+import java.sql.Timestamp;
+import java.util.Objects;
+import java.util.Optional;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ChangeCheckerImpl implements ChangeChecker {
+  private static final Logger log = LoggerFactory.getLogger(ChangeCheckerImpl.class);
+  private final GitRepositoryManager gitRepoMgr;
+  private final CommentsUtil commentsUtil;
+  private final ChangeDb changeDb;
+  private final OneOffRequestContext oneOffReqCtx;
+  private final String changeId;
+  private final ChangeFinder changeFinder;
+  private Optional<Long> computedChangeTs = Optional.empty();
+  private Optional<ChangeNotes> changeNotes = Optional.empty();
+
+  public interface Factory {
+    ChangeChecker create(String changeId);
+  }
+
+  @Inject
+  public ChangeCheckerImpl(
+      GitRepositoryManager gitRepoMgr,
+      CommentsUtil commentsUtil,
+      ChangeDb changeDb,
+      ChangeFinder changeFinder,
+      OneOffRequestContext oneOffReqCtx,
+      @Assisted String changeId) {
+    this.changeFinder = changeFinder;
+    this.gitRepoMgr = gitRepoMgr;
+    this.commentsUtil = commentsUtil;
+    this.changeDb = changeDb;
+    this.oneOffReqCtx = oneOffReqCtx;
+    this.changeId = changeId;
+  }
+
+  @Override
+  public Optional<IndexEvent> newIndexEvent() throws IOException, OrmException {
+    return getComputedChangeTs()
+        .map(
+            ts -> {
+              IndexEvent event = new IndexEvent();
+              event.eventCreatedOn = ts;
+              event.targetSha = getBranchTargetSha();
+              return event;
+            });
+  }
+
+  @Override
+  public Optional<ChangeNotes> getChangeNotes() throws OrmException {
+    try (ManualRequestContext ctx = oneOffReqCtx.open()) {
+      changeNotes = Optional.ofNullable(changeFinder.findOne(changeId));
+      return changeNotes;
+    }
+  }
+
+  @Override
+  public boolean isChangeUpToDate(Optional<IndexEvent> indexEvent)
+      throws IOException, OrmException {
+    getComputedChangeTs();
+    log.debug("Checking change {} against index event {}", this, indexEvent);
+    if (!computedChangeTs.isPresent()) {
+      log.warn("Unable to compute last updated ts for change {}", changeId);
+      return false;
+    }
+
+    if (indexEvent.isPresent() && indexEvent.get().targetSha == null) {
+      return indexEvent.map(e -> (computedChangeTs.get() >= e.eventCreatedOn)).orElse(true);
+    }
+
+    return indexEvent
+        .map(
+            e ->
+                (computedChangeTs.get() > e.eventCreatedOn)
+                    || (computedChangeTs.get() == e.eventCreatedOn)
+                        && (Objects.equals(getBranchTargetSha(), e.targetSha)))
+        .orElse(true);
+  }
+
+  @Override
+  public Optional<Long> getComputedChangeTs() throws IOException, OrmException {
+    if (!computedChangeTs.isPresent()) {
+      computedChangeTs = computeLastChangeTs();
+    }
+    return computedChangeTs;
+  }
+
+  @Override
+  public String toString() {
+    try {
+      return "change-id="
+          + changeId
+          + "@"
+          + getComputedChangeTs().map(IndexEvent::format)
+          + "/"
+          + getBranchTargetSha();
+    } catch (IOException | OrmException e) {
+      log.error("Unable to render change {}", changeId, e);
+      return "change-id=" + changeId;
+    }
+  }
+
+  private String getBranchTargetSha() {
+    try (Repository repo = gitRepoMgr.openRepository(changeNotes.get().getProjectName())) {
+      String refName = changeNotes.get().getChange().getDest().get();
+      Ref ref = repo.exactRef(refName);
+      if (ref == null) {
+        log.warn("Unable to find target ref {} for change {}", refName, changeId);
+        return null;
+      }
+      return ref.getTarget().getObjectId().getName();
+    } catch (IOException e) {
+      log.warn("Unable to resolve target branch SHA for change {}", changeId, e);
+      return null;
+    }
+  }
+
+  private Optional<Long> computeLastChangeTs() throws OrmException {
+    try (ReviewDb db = changeDb.open()) {
+      return getChangeNotes().map(notes -> getTsFromChangeAndDraftComments(db, notes));
+    }
+  }
+
+  private long getTsFromChangeAndDraftComments(ReviewDb db, ChangeNotes notes) {
+    Change change = notes.getChange();
+    Timestamp changeTs = change.getLastUpdatedOn();
+    try {
+      for (Comment comment : commentsUtil.draftByChange(db, changeNotes.get())) {
+        Timestamp commentTs = comment.writtenOn;
+        changeTs = commentTs.after(changeTs) ? commentTs : changeTs;
+      }
+    } catch (OrmException e) {
+      log.warn("Unable to access draft comments for change {}", change, e);
+    }
+    return changeTs.getTime() / 1000;
+  }
+}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeDb.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeDb.java
new file mode 100644
index 0000000..bef5363
--- /dev/null
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ChangeDb.java
@@ -0,0 +1,38 @@
+// Copyright (C) 2018 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.ericsson.gerrit.plugins.highavailability.index;
+
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.notedb.NotesMigration;
+import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.SchemaFactory;
+import com.google.inject.Inject;
+
+public class ChangeDb {
+  private static final DisabledReviewDb disabledReviewDb = new DisabledReviewDb();
+
+  private final NotesMigration migration;
+  private final SchemaFactory<ReviewDb> schemaFactory;
+
+  @Inject
+  public ChangeDb(NotesMigration migration, SchemaFactory<ReviewDb> schemaFactory) {
+    this.migration = migration;
+    this.schemaFactory = schemaFactory;
+  }
+
+  public ReviewDb open() throws OrmException {
+    return migration.readChanges() ? disabledReviewDb : schemaFactory.open();
+  }
+}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/DisabledReviewDb.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/DisabledReviewDb.java
new file mode 100644
index 0000000..25ec6e8
--- /dev/null
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/DisabledReviewDb.java
@@ -0,0 +1,202 @@
+// Copyright (C) 2018 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.ericsson.gerrit.plugins.highavailability.index;
+
+import com.google.common.util.concurrent.CheckedFuture;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Change.Id;
+import com.google.gerrit.reviewdb.server.ChangeAccess;
+import com.google.gerrit.reviewdb.server.ChangeMessageAccess;
+import com.google.gerrit.reviewdb.server.PatchLineCommentAccess;
+import com.google.gerrit.reviewdb.server.PatchSetAccess;
+import com.google.gerrit.reviewdb.server.PatchSetApprovalAccess;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.reviewdb.server.SchemaVersionAccess;
+import com.google.gwtorm.server.Access;
+import com.google.gwtorm.server.AtomicUpdate;
+import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.ResultSet;
+import com.google.gwtorm.server.StatementExecutor;
+import java.util.Map;
+
+/** ReviewDb that is disabled. */
+@SuppressWarnings("deprecation")
+public class DisabledReviewDb implements ReviewDb {
+  public static class Disabled extends RuntimeException {
+    private static final long serialVersionUID = 1L;
+
+    private Disabled() {
+      super("ReviewDb is disabled for changes");
+    }
+  }
+
+  public static class DisabledChangeAccess implements ChangeAccess {
+
+    @Override
+    public String getRelationName() {
+      throw new Disabled();
+    }
+
+    @Override
+    public int getRelationID() {
+      throw new Disabled();
+    }
+
+    @Override
+    public ResultSet<Change> iterateAllEntities() throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public Id primaryKey(Change entity) {
+      throw new Disabled();
+    }
+
+    @Override
+    public Map<Id, Change> toMap(Iterable<Change> c) {
+      throw new Disabled();
+    }
+
+    @Override
+    public CheckedFuture<Change, OrmException> getAsync(Id key) {
+      throw new Disabled();
+    }
+
+    @Override
+    public ResultSet<Change> get(Iterable<Id> keys) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void insert(Iterable<Change> instances) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void update(Iterable<Change> instances) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void upsert(Iterable<Change> instances) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void deleteKeys(Iterable<Id> keys) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void delete(Iterable<Change> instances) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public void beginTransaction(Id key) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public Change atomicUpdate(Id key, AtomicUpdate<Change> update) throws OrmException {
+      throw new Disabled();
+    }
+
+    @Override
+    public Change get(Id id) throws OrmException {
+      return null;
+    }
+
+    @Override
+    public ResultSet<Change> all() throws OrmException {
+      return null;
+    }
+  }
+
+  @Override
+  public void close() {
+    // Do nothing.
+  }
+
+  @Override
+  public void commit() {
+    throw new Disabled();
+  }
+
+  @Override
+  public void rollback() {
+    throw new Disabled();
+  }
+
+  @Override
+  public void updateSchema(StatementExecutor e) {
+    throw new Disabled();
+  }
+
+  @Override
+  public void pruneSchema(StatementExecutor e) {
+    throw new Disabled();
+  }
+
+  @Override
+  public Access<?, ?>[] allRelations() {
+    throw new Disabled();
+  }
+
+  @Override
+  public SchemaVersionAccess schemaVersion() {
+    throw new Disabled();
+  }
+
+  @Override
+  public ChangeAccess changes() {
+    return new DisabledChangeAccess();
+  }
+
+  @Override
+  public PatchSetApprovalAccess patchSetApprovals() {
+    throw new Disabled();
+  }
+
+  @Override
+  public ChangeMessageAccess changeMessages() {
+    throw new Disabled();
+  }
+
+  @Override
+  public PatchSetAccess patchSets() {
+    throw new Disabled();
+  }
+
+  @Override
+  public PatchLineCommentAccess patchComments() {
+    throw new Disabled();
+  }
+
+  @Override
+  public int nextAccountId() {
+    throw new Disabled();
+  }
+
+  @Override
+  public int nextAccountGroupId() {
+    throw new Disabled();
+  }
+
+  @Override
+  public int nextChangeId() {
+    throw new Disabled();
+  }
+}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/PeerInfoNotAvailableException.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutor.java
similarity index 61%
rename from src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/PeerInfoNotAvailableException.java
rename to src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutor.java
index df94f52..44c84dc 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/PeerInfoNotAvailableException.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutor.java
@@ -1,4 +1,4 @@
-// Copyright (C) 2017 The Android Open Source Project
+// Copyright (C) 2018 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.
@@ -12,10 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package com.ericsson.gerrit.plugins.highavailability.forwarder.rest;
+package com.ericsson.gerrit.plugins.highavailability.index;
 
-import java.io.IOException;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
-public class PeerInfoNotAvailableException extends IOException {
-  private static final long serialVersionUID = 1L;
-}
+import com.google.inject.BindingAnnotation;
+import java.lang.annotation.Retention;
+
+@Retention(RUNTIME)
+@BindingAnnotation
+public @interface ForwardedIndexExecutor {}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutorProvider.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutorProvider.java
new file mode 100644
index 0000000..2112dbe
--- /dev/null
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/ForwardedIndexExecutorProvider.java
@@ -0,0 +1,30 @@
+// Copyright (C) 2018 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.ericsson.gerrit.plugins.highavailability.index;
+
+import com.ericsson.gerrit.plugins.highavailability.Configuration;
+import com.ericsson.gerrit.plugins.highavailability.ExecutorProvider;
+import com.google.gerrit.server.git.WorkQueue;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+@Singleton
+class ForwardedIndexExecutorProvider extends ExecutorProvider {
+
+  @Inject
+  ForwardedIndexExecutorProvider(WorkQueue workQueue, Configuration config) {
+    super(workQueue, config.index().threadPoolSize(), "Forwarded-Index-Event");
+  }
+}
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandler.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandler.java
index 106422d..3010689 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandler.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandler.java
@@ -27,20 +27,28 @@
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 class IndexEventHandler
     implements ChangeIndexedListener, AccountIndexedListener, GroupIndexedListener {
+  private static final Logger log = LoggerFactory.getLogger(IndexEventHandler.class);
   private final Executor executor;
   private final Forwarder forwarder;
   private final String pluginName;
   private final Set<IndexTask> queuedTasks = Collections.newSetFromMap(new ConcurrentHashMap<>());
+  private final ChangeCheckerImpl.Factory changeChecker;
 
   @Inject
   IndexEventHandler(
-      @IndexExecutor Executor executor, @PluginName String pluginName, Forwarder forwarder) {
+      @IndexExecutor Executor executor,
+      @PluginName String pluginName,
+      Forwarder forwarder,
+      ChangeCheckerImpl.Factory changeChecker) {
     this.forwarder = forwarder;
     this.executor = executor;
     this.pluginName = pluginName;
+    this.changeChecker = changeChecker;
   }
 
   @Override
@@ -75,9 +83,19 @@
 
   private void executeIndexChangeTask(String projectName, int id, boolean deleted) {
     if (!Context.isForwardedEvent()) {
-      IndexChangeTask task = new IndexChangeTask(projectName, id, deleted);
-      if (queuedTasks.add(task)) {
-        executor.execute(task);
+      ChangeChecker checker = changeChecker.create(projectName + "~" + id);
+      try {
+        checker
+            .newIndexEvent()
+            .map(event -> new IndexChangeTask(projectName, id, deleted, event))
+            .ifPresent(
+                task -> {
+                  if (queuedTasks.add(task)) {
+                    executor.execute(task);
+                  }
+                });
+      } catch (Exception e) {
+        log.warn("Unable to create task to handle change {}~{}", projectName, id, e);
       }
     }
   }
@@ -89,6 +107,10 @@
       indexEvent = new IndexEvent();
     }
 
+    IndexTask(IndexEvent indexEvent) {
+      this.indexEvent = indexEvent;
+    }
+
     @Override
     public void run() {
       queuedTasks.remove(this);
@@ -103,7 +125,8 @@
     private final int changeId;
     private final String projectName;
 
-    IndexChangeTask(String projectName, int changeId, boolean deleted) {
+    IndexChangeTask(String projectName, int changeId, boolean deleted, IndexEvent indexEvent) {
+      super(indexEvent);
       this.projectName = projectName;
       this.changeId = changeId;
       this.deleted = deleted;
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
index f88a806..ebf8fdf 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
@@ -19,16 +19,26 @@
 import com.google.gerrit.extensions.events.GroupIndexedListener;
 import com.google.gerrit.extensions.registration.DynamicSet;
 import com.google.gerrit.lifecycle.LifecycleModule;
+import com.google.inject.assistedinject.FactoryModuleBuilder;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 
 public class IndexModule extends LifecycleModule {
 
   @Override
   protected void configure() {
     bind(Executor.class).annotatedWith(IndexExecutor.class).toProvider(IndexExecutorProvider.class);
+    bind(ScheduledExecutorService.class)
+        .annotatedWith(ForwardedIndexExecutor.class)
+        .toProvider(ForwardedIndexExecutorProvider.class);
     listener().to(IndexExecutorProvider.class);
     DynamicSet.bind(binder(), ChangeIndexedListener.class).to(IndexEventHandler.class);
     DynamicSet.bind(binder(), AccountIndexedListener.class).to(IndexEventHandler.class);
     DynamicSet.bind(binder(), GroupIndexedListener.class).to(IndexEventHandler.class);
+
+    install(
+        new FactoryModuleBuilder()
+            .implement(ChangeChecker.class, ChangeCheckerImpl.class)
+            .build(ChangeCheckerImpl.Factory.class));
   }
 }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PeerInfoModule.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PeerInfoModule.java
index 577d66d..68707c2 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PeerInfoModule.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PeerInfoModule.java
@@ -18,7 +18,7 @@
 import com.ericsson.gerrit.plugins.highavailability.peers.jgroups.JGroupsPeerInfoProvider;
 import com.google.gerrit.lifecycle.LifecycleModule;
 import com.google.inject.TypeLiteral;
-import java.util.Optional;
+import java.util.Set;
 
 public class PeerInfoModule extends LifecycleModule {
 
@@ -32,11 +32,10 @@
   protected void configure() {
     switch (strategy) {
       case STATIC:
-        bind(new TypeLiteral<Optional<PeerInfo>>() {})
-            .toProvider(PluginConfigPeerInfoProvider.class);
+        bind(new TypeLiteral<Set<PeerInfo>>() {}).toProvider(PluginConfigPeerInfoProvider.class);
         break;
       case JGROUPS:
-        bind(new TypeLiteral<Optional<PeerInfo>>() {}).toProvider(JGroupsPeerInfoProvider.class);
+        bind(new TypeLiteral<Set<PeerInfo>>() {}).toProvider(JGroupsPeerInfoProvider.class);
         listener().to(JGroupsPeerInfoProvider.class);
         break;
       default:
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PluginConfigPeerInfoProvider.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PluginConfigPeerInfoProvider.java
index f39eb6b..9233c79 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PluginConfigPeerInfoProvider.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/PluginConfigPeerInfoProvider.java
@@ -18,20 +18,21 @@
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.google.inject.Singleton;
-import java.util.Optional;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 @Singleton
-public class PluginConfigPeerInfoProvider implements Provider<Optional<PeerInfo>> {
+public class PluginConfigPeerInfoProvider implements Provider<Set<PeerInfo>> {
 
-  private final Optional<PeerInfo> peerInfo;
+  private final Set<PeerInfo> peers;
 
   @Inject
   PluginConfigPeerInfoProvider(Configuration cfg) {
-    peerInfo = Optional.of(new PeerInfo(cfg.peerInfoStatic().url()));
+    peers = cfg.peerInfoStatic().urls().stream().map(PeerInfo::new).collect(Collectors.toSet());
   }
 
   @Override
-  public Optional<PeerInfo> get() {
-    return peerInfo;
+  public Set<PeerInfo> get() {
+    return peers;
   }
 }
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/jgroups/JGroupsPeerInfoProvider.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/jgroups/JGroupsPeerInfoProvider.java
index cf46ac3..596f86e 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/jgroups/JGroupsPeerInfoProvider.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/peers/jgroups/JGroupsPeerInfoProvider.java
@@ -16,6 +16,7 @@
 
 import com.ericsson.gerrit.plugins.highavailability.Configuration;
 import com.ericsson.gerrit.plugins.highavailability.peers.PeerInfo;
+import com.google.common.collect.ImmutableSet;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
@@ -23,6 +24,7 @@
 import java.net.InetAddress;
 import java.nio.file.Path;
 import java.util.Optional;
+import java.util.Set;
 import org.jgroups.Address;
 import org.jgroups.JChannel;
 import org.jgroups.Message;
@@ -43,7 +45,7 @@
  */
 @Singleton
 public class JGroupsPeerInfoProvider extends ReceiverAdapter
-    implements Provider<Optional<PeerInfo>>, LifecycleListener {
+    implements Provider<Set<PeerInfo>>, LifecycleListener {
   private static final Logger log = LoggerFactory.getLogger(JGroupsPeerInfoProvider.class);
   private static final String JGROUPS_LOG_FACTORY_PROPERTY = "jgroups.logging.log_factory_class";
 
@@ -85,7 +87,6 @@
   @Override
   public void viewAccepted(View view) {
     log.info("viewAccepted(view: {}) called", view);
-
     synchronized (this) {
       if (view.getMembers().size() > 2) {
         log.warn(
@@ -164,8 +165,8 @@
   }
 
   @Override
-  public Optional<PeerInfo> get() {
-    return peerInfo;
+  public Set<PeerInfo> get() {
+    return peerInfo.isPresent() ? ImmutableSet.of(peerInfo.get()) : ImmutableSet.of();
   }
 
   @Override
diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index 331dae5..b2040d5 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -1,3 +1,4 @@
+
 This plugin allows making Gerrit highly available by having redundant Gerrit
 masters.
 
@@ -7,10 +8,10 @@
 * sharing the git repositories using a shared file system (e.g. NFS)
 * behind a load balancer (e.g. HAProxy)
 
-Currently, the only mode supported is one primary (active) master and one backup
-(passive) master but eventually the plan is to support `n` active masters. In
+Currently, the mode supported is one primary (active) master and multiple backup
+(passive) masters but eventually the plan is to support `n` active masters. In
 the active/passive mode, the active master is handling all traffic while the
-passive is kept updated to be always ready to take over.
+passives are kept updated to be always ready to take over.
 
 Even if database and git repositories are shared by the masters, there are a few
 areas of concern in order to be able to switch traffic between masters in a
@@ -23,38 +24,38 @@
 * web sessions
 
 They need either to be shared or kept local to each master but synchronized.
-This plugin needs to be installed in both masters and will take care of sharing
+This plugin needs to be installed in all the masters and it will take care of sharing
 or synchronizing them.
 
 #### Caches
 Every time a cache eviction occurs in one of the masters, the eviction will be
-forwarded the other master so its caches do not contain stale entries.
+forwarded the other masters so their caches do not contain stale entries.
 
 #### Secondary indexes
 Every time the secondary index is modified in one of the masters, e.g., a change
-is added, updated or removed from the index, the other master's index is
+is added, updated or removed from the index, the others master's index are
 updated accordingly. This way, both indexes are kept synchronized.
 
 #### Stream events
 Every time a stream event occurs in one of the masters (see [more events info]
 (https://gerrit-review.googlesource.com/Documentation/cmd-stream-events.html#events)),
-the event is forwarded to the other master which re-plays it. This way, the
+the event is forwarded to the other masters which re-plays it. This way, the
 output of the stream-events command is the same, no matter which master a client
 is connected to.
 
 #### Web session
 The built-in Gerrit H2 based web session cache is replaced with a file based
-implementation that is shared amongst both masters.
+implementation that is shared amongst the masters.
 
 ## Setup
 
 Prerequisites:
 
-* Unique database server must be accessible from both masters
+* Unique database server must be accessible from all the masters
 * Git repositories must be located on a shared file system
 * A directory on a shared file system must be available for @PLUGIN@ to use
 
-For both masters:
+For the masters:
 
 * Configure database section in gerrit.config to use the shared database
 * Configure gerrit.basePath in gerrit.config to the shared repositories location
@@ -69,7 +70,7 @@
   sharedDirectory = /directory/accessible/from/both/masters
 
 [peerInfo "static"]
-  url = http://backupMasterHost:8081/
+  url = http://backupMasterHost1:8081/
 
 [http]
   user = username
diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index b59b1fc..04ccafc 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -1,7 +1,8 @@
+
 @PLUGIN@ Configuration
 =========================
 
-The @PLUGIN@ plugin must be installed on both instances and the following fields
+The @PLUGIN@ plugin must be installed on all the instances and the following fields
 should be specified in `$site_path/etc/@PLUGIN@.config` file:
 
 File '@PLUGIN@.config'
@@ -17,7 +18,8 @@
 [peerInfo]
   strategy = static
 [peerInfo "static"]
-  url = target_instance_url
+  url = first_target_instance_url
+  url = second_target_instance_url
 [http]
   user = username
   password = password
@@ -93,7 +95,8 @@
 a member joins or leaves the cluster.
 
 ```peerInfo.static.url```
-:   Specify the URL for the peer instance.
+:   Specify the URL for the peer instance. If more than one peer instance is to be
+    configured, add as many url entries as necessary.
 
 ```peerInfo.jgroups.myUrl```
 :   The URL of this instance to be broadcast to other peers. If not specified, the
@@ -192,6 +195,17 @@
 :   Maximum number of threads used to send index events to the target instance.
     Defaults to 4.
 
+```index.maxTries```
+:   Maximum number of times the plugin should attempt to reindex changes.
+    Setting this value to 0 will disable retries. After this number of failed tries,
+    an error is logged and the local index should be considered stale and needs
+    to be investigated and manually reindexed.
+    Defaults to 2.
+
+```index.retryInterval```
+:   The interval of time in milliseconds between the subsequent auto-retries.
+    Defaults to 30000 (30 seconds).
+
 ```websession.synchronize```
 :   Whether to synchronize web sessions.
     Defaults to true.
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/ConfigurationTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/ConfigurationTest.java
index efb3b75..63ab408 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/ConfigurationTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/ConfigurationTest.java
@@ -69,6 +69,7 @@
 import java.io.IOException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.List;
 import org.eclipse.jgit.lib.Config;
 import org.junit.Before;
 import org.junit.Test;
@@ -84,6 +85,7 @@
   private static final String PASS = "fakePass";
   private static final String USER = "fakeUser";
   private static final String URL = "http://fakeUrl";
+  private static final List<String> URLS = ImmutableList.of(URL, "http://anotherUrl/");
   private static final int TIMEOUT = 5000;
   private static final int MAX_TRIES = 5;
   private static final int RETRY_INTERVAL = 1000;
@@ -122,17 +124,12 @@
   }
 
   @Test
-  public void testGetUrl() throws Exception {
-    assertThat(getConfiguration().peerInfoStatic().url()).isEmpty();
+  public void testGetUrls() throws Exception {
+    assertThat(getConfiguration().peerInfoStatic().urls()).isEmpty();
 
-    globalPluginConfig.setString(PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY, URL);
-    assertThat(getConfiguration().peerInfoStatic().url()).isEqualTo(URL);
-  }
-
-  @Test
-  public void testGetUrlIsDroppingTrailingSlash() throws Exception {
-    globalPluginConfig.setString(PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY, URL + "/");
-    assertThat(getConfiguration().peerInfoStatic().url()).isEqualTo(URL);
+    globalPluginConfig.setStringList(PEER_INFO_SECTION, STATIC_SUBSECTION, URL_KEY, URLS);
+    assertThat(getConfiguration().peerInfoStatic().urls())
+        .containsAllIn(ImmutableList.of(URL, "http://anotherUrl"));
   }
 
   @Test
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandlerTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandlerTest.java
index 54cd266..6bfc58b 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandlerTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/ForwardedIndexChangeHandlerTest.java
@@ -25,17 +25,19 @@
 
 import com.ericsson.gerrit.plugins.highavailability.Configuration;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.ForwardedIndexingHandler.Operation;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeChecker;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeCheckerImpl;
+import com.ericsson.gerrit.plugins.highavailability.index.ChangeDb;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.server.ReviewDb;
-import com.google.gerrit.server.change.ChangeFinder;
 import com.google.gerrit.server.index.change.ChangeIndexer;
 import com.google.gerrit.server.notedb.ChangeNotes;
-import com.google.gerrit.server.project.NoSuchChangeException;
+import com.google.gerrit.server.util.OneOffRequestContext;
 import com.google.gerrit.server.util.time.TimeUtil;
 import com.google.gwtorm.server.OrmException;
-import com.google.gwtorm.server.SchemaFactory;
 import java.io.IOException;
 import java.util.Optional;
+import java.util.concurrent.ScheduledExecutorService;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -57,40 +59,58 @@
   private static final boolean DO_NOT_THROW_ORM_EXCEPTION = false;
   private static final boolean THROW_IO_EXCEPTION = true;
   private static final boolean THROW_ORM_EXCEPTION = true;
+  private static final boolean CHANGE_UP_TO_DATE = true;
+  private static final boolean CHANGE_OUTDATED = false;
 
   @Rule public ExpectedException exception = ExpectedException.none();
   @Mock private ChangeIndexer indexerMock;
-  @Mock private SchemaFactory<ReviewDb> schemaFactoryMock;
+  @Mock private ChangeDb changeDbMock;
   @Mock private ReviewDb dbMock;
-  @Mock private ChangeFinder changeFinderMock;
   @Mock private ChangeNotes changeNotes;
   @Mock private Configuration configMock;
   @Mock private Configuration.Index indexMock;
+  @Mock private ScheduledExecutorService indexExecutorMock;
+  @Mock private OneOffRequestContext ctxMock;
+  @Mock private ChangeCheckerImpl.Factory changeCheckerFactoryMock;
+  @Mock private ChangeChecker changeCheckerAbsentMock;
+  @Mock private ChangeChecker changeCheckerPresentMock;
   private ForwardedIndexChangeHandler handler;
   private Change.Id id;
-  private Change change;
 
   @Before
   public void setUp() throws Exception {
-    when(schemaFactoryMock.open()).thenReturn(dbMock);
+    when(changeDbMock.open()).thenReturn(dbMock);
     id = new Change.Id(TEST_CHANGE_NUMBER);
-    change = new Change(null, id, null, null, TimeUtil.nowTs());
+    Change change = new Change(null, id, null, null, TimeUtil.nowTs());
     when(changeNotes.getChange()).thenReturn(change);
     when(configMock.index()).thenReturn(indexMock);
     when(indexMock.numStripedLocks()).thenReturn(10);
+    when(changeCheckerFactoryMock.create(any())).thenReturn(changeCheckerAbsentMock);
     handler =
         new ForwardedIndexChangeHandler(
-            indexerMock, schemaFactoryMock, changeFinderMock, configMock);
+            indexerMock,
+            changeDbMock,
+            configMock,
+            indexExecutorMock,
+            ctxMock,
+            changeCheckerFactoryMock);
   }
 
   @Test
-  public void changeIsIndexed() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_EXISTS);
+  public void changeIsIndexedWhenUpToDate() throws Exception {
+    setupChangeAccessRelatedMocks(CHANGE_EXISTS, CHANGE_UP_TO_DATE);
     handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
     verify(indexerMock, times(1)).index(any(ReviewDb.class), any(Change.class));
   }
 
   @Test
+  public void changeIsStillIndexedEvenWhenOutdated() throws Exception {
+    setupChangeAccessRelatedMocks(CHANGE_EXISTS, CHANGE_OUTDATED);
+    handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.of(new IndexEvent()));
+    verify(indexerMock, times(1)).index(any(ReviewDb.class), any(Change.class));
+  }
+
+  @Test
   public void changeIsDeletedFromIndex() throws Exception {
     handler.index(TEST_CHANGE_ID, Operation.DELETE, Optional.empty());
     verify(indexerMock, times(1)).delete(id);
@@ -98,43 +118,29 @@
 
   @Test
   public void changeToIndexDoesNotExist() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_DOES_NOT_EXIST);
+    setupChangeAccessRelatedMocks(CHANGE_DOES_NOT_EXIST, CHANGE_OUTDATED);
     handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
     verify(indexerMock, times(1)).delete(id);
   }
 
   @Test
   public void schemaThrowsExceptionWhenLookingUpForChange() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_EXISTS, THROW_ORM_EXCEPTION);
+    setupChangeAccessRelatedMocks(CHANGE_EXISTS, THROW_ORM_EXCEPTION, CHANGE_UP_TO_DATE);
     exception.expect(OrmException.class);
     handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
   }
 
   @Test
-  public void indexerThrowsNoSuchChangeExceptionTryingToPostChange() throws Exception {
-    doThrow(new NoSuchChangeException(id)).when(schemaFactoryMock).open();
-    handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
-    verify(indexerMock, times(1)).delete(id);
-  }
-
-  @Test
-  public void indexerThrowsNestedNoSuchChangeExceptionTryingToPostChange() throws Exception {
-    OrmException e = new OrmException("test", new NoSuchChangeException(id));
-    doThrow(e).when(schemaFactoryMock).open();
-    handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
-    verify(indexerMock, times(1)).delete(id);
-  }
-
-  @Test
   public void indexerThrowsIOExceptionTryingToIndexChange() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_EXISTS, DO_NOT_THROW_ORM_EXCEPTION, THROW_IO_EXCEPTION);
+    setupChangeAccessRelatedMocks(
+        CHANGE_EXISTS, DO_NOT_THROW_ORM_EXCEPTION, THROW_IO_EXCEPTION, CHANGE_UP_TO_DATE);
     exception.expect(IOException.class);
     handler.index(TEST_CHANGE_ID, Operation.INDEX, Optional.empty());
   }
 
   @Test
   public void shouldSetAndUnsetForwardedContext() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_EXISTS);
+    setupChangeAccessRelatedMocks(CHANGE_EXISTS, CHANGE_UP_TO_DATE);
     // this doAnswer is to allow to assert that context is set to forwarded
     // while cache eviction is called.
     doAnswer(
@@ -155,7 +161,7 @@
 
   @Test
   public void shouldSetAndUnsetForwardedContextEvenIfExceptionIsThrown() throws Exception {
-    setupChangeAccessRelatedMocks(CHANGE_EXISTS);
+    setupChangeAccessRelatedMocks(CHANGE_EXISTS, CHANGE_UP_TO_DATE);
     doAnswer(
             (Answer<Void>)
                 invocation -> {
@@ -177,33 +183,38 @@
     verify(indexerMock, times(1)).index(any(ReviewDb.class), any(Change.class));
   }
 
-  private void setupChangeAccessRelatedMocks(boolean changeExist) throws Exception {
+  private void setupChangeAccessRelatedMocks(boolean changeExist, boolean changeUpToDate)
+      throws Exception {
     setupChangeAccessRelatedMocks(
-        changeExist, DO_NOT_THROW_ORM_EXCEPTION, DO_NOT_THROW_IO_EXCEPTION);
-  }
-
-  private void setupChangeAccessRelatedMocks(boolean changeExist, boolean ormException)
-      throws OrmException, IOException {
-    setupChangeAccessRelatedMocks(changeExist, ormException, DO_NOT_THROW_IO_EXCEPTION);
+        changeExist, DO_NOT_THROW_ORM_EXCEPTION, DO_NOT_THROW_IO_EXCEPTION, changeUpToDate);
   }
 
   private void setupChangeAccessRelatedMocks(
-      boolean changeExists, boolean ormException, boolean ioException)
+      boolean changeExist, boolean ormException, boolean changeUpToDate)
+      throws OrmException, IOException {
+    setupChangeAccessRelatedMocks(
+        changeExist, ormException, DO_NOT_THROW_IO_EXCEPTION, changeUpToDate);
+  }
+
+  private void setupChangeAccessRelatedMocks(
+      boolean changeExists, boolean ormException, boolean ioException, boolean changeIsUpToDate)
       throws OrmException, IOException {
     if (ormException) {
-      doThrow(new OrmException("")).when(schemaFactoryMock).open();
+      doThrow(new OrmException("")).when(changeDbMock).open();
     } else {
-      when(schemaFactoryMock.open()).thenReturn(dbMock);
-      if (changeExists) {
-        when(changeFinderMock.findOne(TEST_CHANGE_ID)).thenReturn(changeNotes);
-        if (ioException) {
-          doThrow(new IOException("io-error"))
-              .when(indexerMock)
-              .index(any(ReviewDb.class), any(Change.class));
-        }
-      } else {
-        when(changeFinderMock.findOne(TEST_CHANGE_ID)).thenReturn(null);
+      when(changeDbMock.open()).thenReturn(dbMock);
+    }
+
+    if (changeExists) {
+      when(changeCheckerFactoryMock.create(TEST_CHANGE_ID)).thenReturn(changeCheckerPresentMock);
+      when(changeCheckerPresentMock.getChangeNotes()).thenReturn(Optional.of(changeNotes));
+      if (ioException) {
+        doThrow(new IOException("io-error"))
+            .when(indexerMock)
+            .index(any(ReviewDb.class), any(Change.class));
       }
     }
+
+    when(changeCheckerPresentMock.isChangeUpToDate(any())).thenReturn(changeIsUpToDate);
   }
 }
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSessionTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSessionTest.java
index b6eba3d..5e0d4c9 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSessionTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/HttpSessionTest.java
@@ -15,35 +15,27 @@
 package com.ericsson.gerrit.plugins.highavailability.forwarder.rest;
 
 import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
-import static com.github.tomakehurst.wiremock.client.WireMock.anyRequestedFor;
-import static com.github.tomakehurst.wiremock.client.WireMock.anyUrl;
 import static com.github.tomakehurst.wiremock.client.WireMock.delete;
 import static com.github.tomakehurst.wiremock.client.WireMock.equalTo;
-import static com.github.tomakehurst.wiremock.client.WireMock.exactly;
 import static com.github.tomakehurst.wiremock.client.WireMock.post;
 import static com.github.tomakehurst.wiremock.client.WireMock.urlEqualTo;
-import static com.github.tomakehurst.wiremock.client.WireMock.verify;
 import static com.google.common.truth.Truth.assertThat;
-import static org.junit.Assert.fail;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
 import com.ericsson.gerrit.plugins.highavailability.Configuration;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.rest.HttpResponseHandler.HttpResult;
-import com.ericsson.gerrit.plugins.highavailability.peers.PeerInfo;
 import com.github.tomakehurst.wiremock.http.Fault;
 import com.github.tomakehurst.wiremock.junit.WireMockRule;
 import com.github.tomakehurst.wiremock.stubbing.Scenario;
-import com.google.inject.util.Providers;
-import java.io.IOException;
 import java.net.SocketTimeoutException;
-import java.util.Optional;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.mockito.Answers;
 
 public class HttpSessionTest {
+
   private static final int MAX_TRIES = 3;
   private static final int RETRY_INTERVAL = 250;
   private static final int TIMEOUT = 500;
@@ -64,12 +56,13 @@
 
   @Rule public WireMockRule wireMockRule = new WireMockRule(0);
 
-  private Configuration configMock;
+  private String uri;
 
   @Before
   public void setUp() throws Exception {
     String url = "http://localhost:" + wireMockRule.port();
-    configMock = mock(Configuration.class, Answers.RETURNS_DEEP_STUBS);
+    uri = url + ENDPOINT;
+    Configuration configMock = mock(Configuration.class, Answers.RETURNS_DEEP_STUBS);
     when(configMock.http().user()).thenReturn("user");
     when(configMock.http().password()).thenReturn("pass");
     when(configMock.http().maxTries()).thenReturn(MAX_TRIES);
@@ -77,11 +70,7 @@
     when(configMock.http().socketTimeout()).thenReturn(TIMEOUT);
     when(configMock.http().retryInterval()).thenReturn(RETRY_INTERVAL);
 
-    PeerInfo peerInfo = mock(PeerInfo.class);
-    when(peerInfo.getDirectUrl()).thenReturn(url);
-    httpSession =
-        new HttpSession(
-            new HttpClientProvider(configMock).get(), Providers.of(Optional.of(peerInfo)));
+    httpSession = new HttpSession(new HttpClientProvider(configMock).get());
   }
 
   @Test
@@ -89,7 +78,7 @@
     wireMockRule.givenThat(
         post(urlEqualTo(ENDPOINT)).willReturn(aResponse().withStatus(NO_CONTENT)));
 
-    assertThat(httpSession.post(ENDPOINT).isSuccessful()).isTrue();
+    assertThat(httpSession.post(uri).isSuccessful()).isTrue();
   }
 
   @Test
@@ -98,7 +87,7 @@
         post(urlEqualTo(ENDPOINT))
             .withRequestBody(equalTo(BODY))
             .willReturn(aResponse().withStatus(NO_CONTENT)));
-    assertThat(httpSession.post(ENDPOINT, BODY).isSuccessful()).isTrue();
+    assertThat(httpSession.post(uri, BODY).isSuccessful()).isTrue();
   }
 
   @Test
@@ -106,7 +95,7 @@
     wireMockRule.givenThat(
         delete(urlEqualTo(ENDPOINT)).willReturn(aResponse().withStatus(NO_CONTENT)));
 
-    assertThat(httpSession.delete(ENDPOINT).isSuccessful()).isTrue();
+    assertThat(httpSession.delete(uri).isSuccessful()).isTrue();
   }
 
   @Test
@@ -116,7 +105,7 @@
         post(urlEqualTo(ENDPOINT))
             .willReturn(aResponse().withStatus(UNAUTHORIZED).withBody(expected)));
 
-    HttpResult result = httpSession.post(ENDPOINT);
+    HttpResult result = httpSession.post(uri);
     assertThat(result.isSuccessful()).isFalse();
     assertThat(result.getMessage()).isEqualTo(expected);
   }
@@ -128,7 +117,7 @@
         post(urlEqualTo(ENDPOINT))
             .willReturn(aResponse().withStatus(NOT_FOUND).withBody(expected)));
 
-    HttpResult result = httpSession.post(ENDPOINT);
+    HttpResult result = httpSession.post(uri);
     assertThat(result.isSuccessful()).isFalse();
     assertThat(result.getMessage()).isEqualTo(expected);
   }
@@ -139,7 +128,7 @@
         post(urlEqualTo(ENDPOINT))
             .willReturn(aResponse().withStatus(ERROR).withBody(ERROR_MESSAGE)));
 
-    HttpResult result = httpSession.post(ENDPOINT);
+    HttpResult result = httpSession.post(uri);
     assertThat(result.isSuccessful()).isFalse();
     assertThat(result.getMessage()).isEqualTo(ERROR_MESSAGE);
   }
@@ -170,7 +159,7 @@
             .whenScenarioStateIs(THIRD_TRY)
             .willReturn(aResponse().withFixedDelay(TIMEOUT)));
 
-    httpSession.post(ENDPOINT);
+    httpSession.post(uri);
   }
 
   @Test
@@ -179,19 +168,6 @@
         post(urlEqualTo(ENDPOINT))
             .willReturn(aResponse().withFault(Fault.MALFORMED_RESPONSE_CHUNK)));
 
-    assertThat(httpSession.post(ENDPOINT).isSuccessful()).isFalse();
-  }
-
-  @Test
-  public void testNoRequestWhenPeerInfoUnknown() throws IOException {
-    httpSession =
-        new HttpSession(new HttpClientProvider(configMock).get(), Providers.of(Optional.empty()));
-    try {
-      httpSession.post(ENDPOINT);
-      fail("Expected PeerInfoNotAvailableException");
-    } catch (PeerInfoNotAvailableException e) {
-      // good
-    }
-    verify(exactly(0), anyRequestedFor(anyUrl()));
+    assertThat(httpSession.post(uri).isSuccessful()).isFalse();
   }
 }
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarderTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarderTest.java
index fd2aa52..c5b52a0 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarderTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/forwarder/rest/RestForwarderTest.java
@@ -26,22 +26,27 @@
 import com.ericsson.gerrit.plugins.highavailability.cache.Constants;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.IndexEvent;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.rest.HttpResponseHandler.HttpResult;
+import com.ericsson.gerrit.plugins.highavailability.peers.PeerInfo;
 import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableSet;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.server.events.Event;
 import com.google.gson.GsonBuilder;
+import com.google.inject.Provider;
 import java.io.IOException;
+import java.util.Set;
 import javax.net.ssl.SSLException;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.Answers;
 
 public class RestForwarderTest {
+  private static final String URL = "http://fake.com";
   private static final String PLUGIN_NAME = "high-availability";
   private static final String EMPTY_MSG = "";
   private static final String ERROR = "Error";
-  private static final String PLUGINS = "/plugins";
+  private static final String PLUGINS = "plugins";
   private static final String PROJECT_TO_ADD = "projectToAdd";
   private static final String PROJECT_TO_DELETE = "projectToDelete";
   private static final String SUCCESS = "Success";
@@ -54,30 +59,41 @@
   private static final String PROJECT_NAME_URL_END = "test%2Fproject";
   private static final String INDEX_CHANGE_ENDPOINT =
       Joiner.on("/")
-          .join(PLUGINS, PLUGIN_NAME, "index/change", PROJECT_NAME_URL_END + "~" + CHANGE_NUMBER);
+          .join(
+              URL,
+              PLUGINS,
+              PLUGIN_NAME,
+              "index/change",
+              PROJECT_NAME_URL_END + "~" + CHANGE_NUMBER);
   private static final String DELETE_CHANGE_ENDPOINT =
-      Joiner.on("/").join("/plugins", PLUGIN_NAME, "index/change", "~" + CHANGE_NUMBER);
+      Joiner.on("/").join(URL, PLUGINS, PLUGIN_NAME, "index/change", "~" + CHANGE_NUMBER);
   private static final int ACCOUNT_NUMBER = 2;
   private static final String INDEX_ACCOUNT_ENDPOINT =
-      Joiner.on("/").join(PLUGINS, PLUGIN_NAME, "index/account", ACCOUNT_NUMBER);
+      Joiner.on("/").join(URL, PLUGINS, PLUGIN_NAME, "index/account", ACCOUNT_NUMBER);
   private static final String UUID = "we235jdf92nfj2351";
   private static final String INDEX_GROUP_ENDPOINT =
-      Joiner.on("/").join(PLUGINS, PLUGIN_NAME, "index/group", UUID);
+      Joiner.on("/").join(URL, PLUGINS, PLUGIN_NAME, "index/group", UUID);
 
   // Event
-  private static final String EVENT_ENDPOINT = Joiner.on("/").join(PLUGINS, PLUGIN_NAME, "event");
   private static Event event = new Event("test-event") {};
+  private static final String EVENT_ENDPOINT =
+      Joiner.on("/").join(URL, PLUGINS, PLUGIN_NAME, "event", event.type);
 
   private RestForwarder forwarder;
   private HttpSession httpSessionMock;
 
+  @SuppressWarnings("unchecked")
   @Before
   public void setUp() {
     httpSessionMock = mock(HttpSession.class);
     Configuration configMock = mock(Configuration.class, Answers.RETURNS_DEEP_STUBS);
     when(configMock.http().maxTries()).thenReturn(3);
     when(configMock.http().retryInterval()).thenReturn(10);
-    forwarder = new RestForwarder(httpSessionMock, PLUGIN_NAME, configMock);
+    Provider<Set<PeerInfo>> peersMock = mock(Provider.class);
+    when(peersMock.get()).thenReturn(ImmutableSet.of(new PeerInfo(URL)));
+    forwarder =
+        new RestForwarder(
+            httpSessionMock, PLUGIN_NAME, configMock, peersMock); // TODO: Create provider
   }
 
   @Test
@@ -142,21 +158,21 @@
 
   @Test
   public void testChangeDeletedFromIndexOK() throws Exception {
-    when(httpSessionMock.delete(eq(DELETE_CHANGE_ENDPOINT), any()))
+    when(httpSessionMock.delete(eq(DELETE_CHANGE_ENDPOINT)))
         .thenReturn(new HttpResult(SUCCESSFUL, EMPTY_MSG));
     assertThat(forwarder.deleteChangeFromIndex(CHANGE_NUMBER, new IndexEvent())).isTrue();
   }
 
   @Test
   public void testChangeDeletedFromIndexFailed() throws Exception {
-    when(httpSessionMock.delete(eq(DELETE_CHANGE_ENDPOINT), any()))
+    when(httpSessionMock.delete(eq(DELETE_CHANGE_ENDPOINT)))
         .thenReturn(new HttpResult(FAILED, EMPTY_MSG));
     assertThat(forwarder.deleteChangeFromIndex(CHANGE_NUMBER, new IndexEvent())).isFalse();
   }
 
   @Test
   public void testChangeDeletedFromThrowsException() throws Exception {
-    doThrow(new IOException()).when(httpSessionMock).delete(eq(DELETE_CHANGE_ENDPOINT), any());
+    doThrow(new IOException()).when(httpSessionMock).delete(eq(DELETE_CHANGE_ENDPOINT));
     assertThat(forwarder.deleteChangeFromIndex(CHANGE_NUMBER, new IndexEvent())).isFalse();
   }
 
@@ -201,8 +217,8 @@
   public void testEvictGroupsOK() throws Exception {
     AccountGroup.Id key = new AccountGroup.Id(123);
     String keyJson = new GsonBuilder().create().toJson(key);
-    when(httpSessionMock.post(buildCacheEndpoint(Constants.GROUPS), keyJson))
-        .thenReturn(new HttpResult(SUCCESSFUL, EMPTY_MSG));
+    String endpoint = buildCacheEndpoint(Constants.GROUPS);
+    when(httpSessionMock.post(endpoint, keyJson)).thenReturn(new HttpResult(SUCCESSFUL, EMPTY_MSG));
     assertThat(forwarder.evict(Constants.GROUPS, key)).isTrue();
   }
 
@@ -244,13 +260,13 @@
   }
 
   private static String buildCacheEndpoint(String name) {
-    return Joiner.on("/").join(PLUGINS, PLUGIN_NAME, "cache", name);
+    return Joiner.on("/").join(URL, PLUGINS, PLUGIN_NAME, "cache", name);
   }
 
   @Test
   public void testAddToProjectListOK() throws Exception {
     String projectName = PROJECT_TO_ADD;
-    when(httpSessionMock.post(buildProjectListCacheEndpoint(projectName)))
+    when(httpSessionMock.post(buildProjectListCacheEndpoint(projectName), null))
         .thenReturn(new HttpResult(SUCCESSFUL, EMPTY_MSG));
     assertThat(forwarder.addToProjectList(projectName)).isTrue();
   }
@@ -258,7 +274,7 @@
   @Test
   public void testAddToProjectListFailed() throws Exception {
     String projectName = PROJECT_TO_ADD;
-    when(httpSessionMock.post(buildProjectListCacheEndpoint(projectName)))
+    when(httpSessionMock.post(buildProjectListCacheEndpoint(projectName), null))
         .thenReturn(new HttpResult(FAILED, EMPTY_MSG));
     assertThat(forwarder.addToProjectList(projectName)).isFalse();
   }
@@ -268,7 +284,7 @@
     String projectName = PROJECT_TO_ADD;
     doThrow(new IOException())
         .when(httpSessionMock)
-        .post(buildProjectListCacheEndpoint(projectName));
+        .post(buildProjectListCacheEndpoint(projectName), null);
     assertThat(forwarder.addToProjectList(projectName)).isFalse();
   }
 
diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
index 43c2fd7..3ec979c 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/index/IndexEventHandlerTest.java
@@ -21,9 +21,11 @@
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyZeroInteractions;
+import static org.mockito.Mockito.when;
 
 import com.ericsson.gerrit.plugins.highavailability.forwarder.Context;
 import com.ericsson.gerrit.plugins.highavailability.forwarder.Forwarder;
+import com.ericsson.gerrit.plugins.highavailability.forwarder.IndexEvent;
 import com.ericsson.gerrit.plugins.highavailability.index.IndexEventHandler.IndexAccountTask;
 import com.ericsson.gerrit.plugins.highavailability.index.IndexEventHandler.IndexChangeTask;
 import com.ericsson.gerrit.plugins.highavailability.index.IndexEventHandler.IndexGroupTask;
@@ -31,6 +33,7 @@
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.AccountGroup;
 import com.google.gerrit.reviewdb.client.Change;
+import java.util.Optional;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 import org.junit.Before;
 import org.junit.Test;
@@ -49,17 +52,22 @@
 
   private IndexEventHandler indexEventHandler;
   @Mock private Forwarder forwarder;
+  @Mock private ChangeCheckerImpl.Factory changeCheckerFactoryMock;
+  @Mock private ChangeChecker changeCheckerMock;
   private Change.Id changeId;
   private Account.Id accountId;
   private AccountGroup.UUID accountGroupUUID;
 
   @Before
-  public void setUpMocks() {
+  public void setUpMocks() throws Exception {
     changeId = new Change.Id(CHANGE_ID);
     accountId = new Account.Id(ACCOUNT_ID);
     accountGroupUUID = new AccountGroup.UUID(UUID);
+    when(changeCheckerFactoryMock.create(any())).thenReturn(changeCheckerMock);
+    when(changeCheckerMock.newIndexEvent()).thenReturn(Optional.of(new IndexEvent()));
     indexEventHandler =
-        new IndexEventHandler(MoreExecutors.directExecutor(), PLUGIN_NAME, forwarder);
+        new IndexEventHandler(
+            MoreExecutors.directExecutor(), PLUGIN_NAME, forwarder, changeCheckerFactoryMock);
   }
 
   @Test
@@ -116,17 +124,19 @@
   @Test
   public void duplicateChangeEventOfAQueuedEventShouldGetDiscarded() {
     ScheduledThreadPoolExecutor poolMock = mock(ScheduledThreadPoolExecutor.class);
-    indexEventHandler = new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder);
+    indexEventHandler =
+        new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder, changeCheckerFactoryMock);
     indexEventHandler.onChangeIndexed(PROJECT_NAME, changeId.get());
     indexEventHandler.onChangeIndexed(PROJECT_NAME, changeId.get());
     verify(poolMock, times(1))
-        .execute(indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false));
+        .execute(indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false, null));
   }
 
   @Test
   public void duplicateAccountEventOfAQueuedEventShouldGetDiscarded() {
     ScheduledThreadPoolExecutor poolMock = mock(ScheduledThreadPoolExecutor.class);
-    indexEventHandler = new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder);
+    indexEventHandler =
+        new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder, changeCheckerFactoryMock);
     indexEventHandler.onAccountIndexed(accountId.get());
     indexEventHandler.onAccountIndexed(accountId.get());
     verify(poolMock, times(1)).execute(indexEventHandler.new IndexAccountTask(ACCOUNT_ID));
@@ -135,7 +145,8 @@
   @Test
   public void duplicateGroupEventOfAQueuedEventShouldGetDiscarded() {
     ScheduledThreadPoolExecutor poolMock = mock(ScheduledThreadPoolExecutor.class);
-    indexEventHandler = new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder);
+    indexEventHandler =
+        new IndexEventHandler(poolMock, PLUGIN_NAME, forwarder, changeCheckerFactoryMock);
     indexEventHandler.onGroupIndexed(accountGroupUUID.get());
     indexEventHandler.onGroupIndexed(accountGroupUUID.get());
     verify(poolMock, times(1)).execute(indexEventHandler.new IndexGroupTask(UUID));
@@ -143,7 +154,8 @@
 
   @Test
   public void testIndexChangeTaskToString() throws Exception {
-    IndexChangeTask task = indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false);
+    IndexChangeTask task =
+        indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false, null);
     assertThat(task.toString())
         .isEqualTo(
             String.format("[%s] Index change %s in target instance", PLUGIN_NAME, CHANGE_ID));
@@ -166,29 +178,31 @@
 
   @Test
   public void testIndexChangeTaskHashCodeAndEquals() {
-    IndexChangeTask task = indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false);
+    IndexChangeTask task =
+        indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false, null);
 
     IndexChangeTask sameTask = task;
     assertThat(task.equals(sameTask)).isTrue();
     assertThat(task.hashCode()).isEqualTo(sameTask.hashCode());
 
     IndexChangeTask identicalTask =
-        indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false);
+        indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID, false, null);
     assertThat(task.equals(identicalTask)).isTrue();
     assertThat(task.hashCode()).isEqualTo(identicalTask.hashCode());
 
     assertThat(task.equals(null)).isFalse();
     assertThat(
-            task.equals(indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID + 1, false)))
+            task.equals(
+                indexEventHandler.new IndexChangeTask(PROJECT_NAME, CHANGE_ID + 1, false, null)))
         .isFalse();
     assertThat(task.hashCode()).isNotEqualTo("test".hashCode());
 
     IndexChangeTask differentChangeIdTask =
-        indexEventHandler.new IndexChangeTask(PROJECT_NAME, 123, false);
+        indexEventHandler.new IndexChangeTask(PROJECT_NAME, 123, false, null);
     assertThat(task.equals(differentChangeIdTask)).isFalse();
     assertThat(task.hashCode()).isNotEqualTo(differentChangeIdTask.hashCode());
 
-    IndexChangeTask removeTask = indexEventHandler.new IndexChangeTask("", CHANGE_ID, true);
+    IndexChangeTask removeTask = indexEventHandler.new IndexChangeTask("", CHANGE_ID, true, null);
     assertThat(task.equals(removeTask)).isFalse();
     assertThat(task.hashCode()).isNotEqualTo(removeTask.hashCode());
   }