diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java b/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
index fe5dbad..782ff4f 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
@@ -67,6 +67,11 @@
   }
 
   @Override
+  public int getDistributionInterval() {
+    return currentConfig.getDistributionInterval();
+  }
+
+  @Override
   public synchronized int getMaxRefsToLog() {
     return currentConfig.getMaxRefsToLog();
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/CreateProjectTask.java b/src/main/java/com/googlesource/gerrit/plugins/replication/CreateProjectTask.java
index fa26e82..424648e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/CreateProjectTask.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/CreateProjectTask.java
@@ -63,7 +63,8 @@
       return true;
     }
 
-    repLog.warn("Cannot create new project {} on remote site {}.", projectName, replicateURI);
+    repLog.atWarning().log(
+        "Cannot create new project %s on remote site %s.", projectName, replicateURI);
     return false;
   }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/DeleteProjectTask.java b/src/main/java/com/googlesource/gerrit/plugins/replication/DeleteProjectTask.java
index 4617672..8ea7227 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/DeleteProjectTask.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/DeleteProjectTask.java
@@ -55,7 +55,7 @@
       return;
     }
 
-    repLog.warn("Cannot delete project {} on remote site {}.", project, replicateURI);
+    repLog.atWarning().log("Cannot delete project %s on remote site %s.", project, replicateURI);
   }
 
   @Override
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java b/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
index 85c3917..6907ad0 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
@@ -14,6 +14,7 @@
 
 package com.googlesource.gerrit.plugins.replication;
 
+import static com.google.gerrit.server.project.ProjectCache.noSuchProject;
 import static com.googlesource.gerrit.plugins.replication.PushResultProcessing.resolveNodeName;
 import static com.googlesource.gerrit.plugins.replication.ReplicationFileBasedConfig.replaceName;
 import static org.eclipse.jgit.transport.RemoteRefUpdate.Status.NON_EXISTING;
@@ -30,6 +31,7 @@
 import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
+import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.extensions.config.FactoryModule;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.extensions.restapi.AuthException;
@@ -51,6 +53,7 @@
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.gerrit.server.util.RequestContext;
+import com.google.gerrit.util.logging.NamedFluentLogger;
 import com.google.inject.Inject;
 import com.google.inject.Injector;
 import com.google.inject.Provider;
@@ -64,10 +67,13 @@
 import java.io.UnsupportedEncodingException;
 import java.net.URLEncoder;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
@@ -81,10 +87,9 @@
 import org.eclipse.jgit.transport.RemoteConfig;
 import org.eclipse.jgit.transport.RemoteRefUpdate;
 import org.eclipse.jgit.transport.URIish;
-import org.slf4j.Logger;
 
 public class Destination {
-  private static final Logger repLog = ReplicationQueue.repLog;
+  private static final NamedFluentLogger repLog = ReplicationQueue.repLog;
 
   private static final String PROJECT_NOT_AVAILABLE = "source project %s not available";
 
@@ -94,7 +99,9 @@
 
   private final ReplicationStateListener stateLog;
   private final Object stateLock = new Object();
-  private final Map<URIish, PushOne> pending = new HashMap<>();
+  // writes are covered by the stateLock, but some reads are still
+  // allowed without the lock
+  private final ConcurrentMap<URIish, PushOne> pending = new ConcurrentHashMap<>();
   private final Map<URIish, PushOne> inFlight = new HashMap<>();
   private final PushOne.Factory opFactory;
   private final DeleteProjectTask.Factory deleteProjectFactory;
@@ -156,7 +163,7 @@
           builder.add(g.getUUID());
           addRecursiveParents(g.getUUID(), builder, groupIncludeCache);
         } else {
-          repLog.warn("Group \"{}\" not recognized, removing from authGroup", name);
+          repLog.atWarning().log("Group \"%s\" not recognized, removing from authGroup", name);
         }
       }
       remoteUser = new RemoteSiteUser(new ListGroupMembership(builder.build()));
@@ -240,11 +247,9 @@
         int numInFlight = inFlight.size();
 
         if (numPending > 0 || numInFlight > 0) {
-          repLog.warn(
-              "Cancelling replication events (pending={}, inFlight={}) for destination {}",
-              numPending,
-              numInFlight,
-              getRemoteConfigName());
+          repLog.atWarning().log(
+              "Cancelling replication events (pending=%d, inFlight=%d) for destination %s",
+              numPending, numInFlight, getRemoteConfigName());
 
           foreachPushOp(
               pending,
@@ -280,7 +285,8 @@
     if (!config.replicateHiddenProjects()
         && state.getProject().getState()
             == com.google.gerrit.extensions.client.ProjectState.HIDDEN) {
-      repLog.debug("Project {} is hidden and replication of hidden projects is disabled", name);
+      repLog.atFine().log(
+          "Project %s is hidden and replication of hidden projects is disabled", name);
       return false;
     }
 
@@ -293,10 +299,9 @@
       permissionBackend.user(user).project(state.getNameKey()).check(permissionToCheck);
       return true;
     } catch (AuthException e) {
-      repLog.debug(
-          "Project {} is not visible to current user {}",
-          name,
-          user.getUserName().orElse("unknown"));
+      repLog.atFine().log(
+          "Project %s is not visible to current user %s",
+          name, user.getUserName().orElse("unknown"));
       return false;
     }
   }
@@ -309,21 +314,22 @@
               () -> {
                 ProjectState projectState;
                 try {
-                  projectState = projectCache.checkedGet(project);
-                } catch (IOException e) {
-                  repLog.warn("Error reading project {} from cache", project, e);
+                  projectState = projectCache.get(project).orElseThrow(noSuchProject(project));
+                } catch (StorageException e) {
+                  repLog.atWarning().withCause(e).log(
+                      "Error reading project %s from cache", project);
                   return false;
                 }
                 if (projectState == null) {
-                  repLog.debug("Project {} does not exist", project);
+                  repLog.atFine().log("Project %s does not exist", project);
                   throw new NoSuchProjectException(project);
                 }
                 if (!projectState.statePermitsRead()) {
-                  repLog.debug("Project {} does not permit read", project);
+                  repLog.atFine().log("Project %s does not permit read", project);
                   return false;
                 }
                 if (!shouldReplicate(projectState, userProvider.get())) {
-                  repLog.debug("Project {} should not be replicated", project);
+                  repLog.atFine().log("Project %s should not be replicated", project);
                   return false;
                 }
                 if (PushOne.ALL_REFS.equals(ref)) {
@@ -336,11 +342,9 @@
                       .ref(ref)
                       .check(RefPermission.READ);
                 } catch (AuthException e) {
-                  repLog.debug(
-                      "Ref {} on project {} is not visible to calling user {}",
-                      ref,
-                      project,
-                      userProvider.get().getUserName().orElse("unknown"));
+                  repLog.atFine().log(
+                      "Ref %s on project %s is not visible to calling user %s",
+                      ref, project, userProvider.get().getUserName().orElse("unknown"));
                   return false;
                 }
                 return true;
@@ -362,13 +366,10 @@
               () -> {
                 ProjectState projectState;
                 try {
-                  projectState = projectCache.checkedGet(project);
-                } catch (IOException e) {
+                  projectState = projectCache.get(project).orElseThrow(noSuchProject(project));
+                } catch (StorageException e) {
                   return false;
                 }
-                if (projectState == null) {
-                  throw new NoSuchProjectException(project);
-                }
                 return shouldReplicate(projectState, userProvider.get());
               })
           .call();
@@ -388,10 +389,10 @@
   void schedule(
       Project.NameKey project, String ref, URIish uri, ReplicationState state, boolean now) {
     if (!shouldReplicate(project, ref, state)) {
-      repLog.debug("Not scheduling replication {}:{} => {}", project, ref, uri);
+      repLog.atFine().log("Not scheduling replication %s:%s => %s", project, ref, uri);
       return;
     }
-    repLog.info("scheduling replication {}:{} => {}", project, ref, uri);
+    repLog.atInfo().log("scheduling replication %s:%s => %s", project, ref, uri);
 
     if (!config.replicatePermissions()) {
       PushOne e;
@@ -433,7 +434,8 @@
         task.addState(ref, state);
       }
       state.increasePushTaskCount(project.get(), ref);
-      repLog.info("scheduled {}:{} => {} to run after {}s", project, ref, task, config.getDelay());
+      repLog.atInfo().log(
+          "scheduled %s:%s => %s to run after %ds", project, ref, task, config.getDelay());
     }
   }
 
@@ -580,7 +582,9 @@
       if (inFlightOp != null) {
         return RunwayStatus.denied(inFlightOp.getId());
       }
-      replicationTasksStorage.get().start(op);
+      if (!replicationTasksStorage.get().start(op)) {
+        return RunwayStatus.deniedExternal();
+      }
       inFlight.put(op.getURI(), op);
     }
     return RunwayStatus.allowed();
@@ -595,9 +599,20 @@
     }
   }
 
+  public Set<String> getPrunableTaskNames() {
+    Set<String> names = new HashSet<>();
+    for (PushOne push : pending.values()) {
+      if (!replicationTasksStorage.get().isWaiting(push)) {
+        repLog.atFine().log("No longer isWaiting, can prune %s", push.getURI());
+        names.add(push.toString());
+      }
+    }
+    return names;
+  }
+
   boolean wouldPushProject(Project.NameKey project) {
     if (!shouldReplicate(project)) {
-      repLog.debug("Skipping replication of project {}", project.get());
+      repLog.atFine().log("Skipping replication of project %s", project.get());
       return false;
     }
 
@@ -609,7 +624,8 @@
 
     boolean matches = (new ReplicationFilter(projects)).matches(project);
     if (!matches) {
-      repLog.debug("Skipping replication of project {}; does not match filter", project.get());
+      repLog.atFine().log(
+          "Skipping replication of project %s; does not match filter", project.get());
     }
     return matches;
   }
@@ -620,7 +636,7 @@
 
   boolean wouldPushRef(String ref) {
     if (!config.replicatePermissions() && RefNames.REFS_CONFIG.equals(ref)) {
-      repLog.debug("Skipping push of ref {}; it is a meta ref", ref);
+      repLog.atFine().log("Skipping push of ref %s; it is a meta ref", ref);
       return false;
     }
     if (PushOne.ALL_REFS.equals(ref)) {
@@ -631,7 +647,7 @@
         return true;
       }
     }
-    repLog.debug("Skipping push of ref {}; it does not match push ref specs", ref);
+    repLog.atFine().log("Skipping push of ref %s; it does not match push ref specs", ref);
     return false;
   }
 
@@ -671,7 +687,7 @@
     } else if (remoteNameStyle.equals("basenameOnly")) {
       name = FilenameUtils.getBaseName(name);
     } else if (!remoteNameStyle.equals("slash")) {
-      repLog.debug("Unknown remoteNameStyle: {}, falling back to slash", remoteNameStyle);
+      repLog.atFine().log("Unknown remoteNameStyle: %s, falling back to slash", remoteNameStyle);
     }
     String replacedPath = replaceName(template.getPath(), name, isSingleProjectMatch());
     return (replacedPath != null) ? template.setPath(replacedPath) : template;
@@ -757,7 +773,7 @@
       try {
         eventDispatcher.get().postEvent(BranchNameKey.create(project, ref), event);
       } catch (PermissionBackendException e) {
-        repLog.error("error posting event", e);
+        repLog.atSevere().withCause(e).log("error posting event");
       }
     }
   }
@@ -771,7 +787,7 @@
       try {
         eventDispatcher.get().postEvent(BranchNameKey.create(project, ref), event);
       } catch (PermissionBackendException e) {
-        repLog.error("error posting event", e);
+        repLog.atSevere().withCause(e).log("error posting event");
       }
     }
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationConfigParser.java b/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationConfigParser.java
index 4050c9c..9b6d431 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationConfigParser.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationConfigParser.java
@@ -14,6 +14,8 @@
 
 package com.googlesource.gerrit.plugins.replication;
 
+import static com.googlesource.gerrit.plugins.replication.ReplicationQueue.repLog;
+
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 import com.google.common.flogger.FluentLogger;
@@ -54,6 +56,11 @@
         continue;
       }
 
+      if (!c.getFetchRefSpecs().isEmpty()) {
+        repLog.atInfo().log("Ignore '%s' endpoint: not a 'push' target", c.getName());
+        continue;
+      }
+
       // If destination for push is not set assume equal to source.
       for (RefSpec ref : c.getPushRefSpecs()) {
         if (ref.getDestination() == null) {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationsCollection.java b/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationsCollection.java
index 71c38d0..d869e83 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationsCollection.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/DestinationsCollection.java
@@ -106,7 +106,7 @@
         try {
           uri = new URIish(url);
         } catch (URISyntaxException e) {
-          repLog.warn("adminURL '{}' is invalid: {}", url, e.getMessage());
+          repLog.atWarning().log("adminURL '%s' is invalid: %s", url, e.getMessage());
           continue;
         }
 
@@ -114,13 +114,14 @@
           String path =
               replaceName(uri.getPath(), projectName.get(), config.isSingleProjectMatch());
           if (path == null) {
-            repLog.warn("adminURL {} does not contain ${name}", uri);
+            repLog.atWarning().log("adminURL %s does not contain ${name}", uri);
             continue;
           }
 
           uri = uri.setPath(path);
           if (!isSSH(uri)) {
-            repLog.warn("adminURL '{}' is invalid: only SSH and HTTP are supported", uri);
+            repLog.atWarning().log(
+                "adminURL '%s' is invalid: only SSH and HTTP are supported", uri);
             continue;
           }
         }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/FanoutReplicationConfig.java b/src/main/java/com/googlesource/gerrit/plugins/replication/FanoutReplicationConfig.java
index 4cc9974..5b24bf5 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/FanoutReplicationConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/FanoutReplicationConfig.java
@@ -152,6 +152,11 @@
   }
 
   @Override
+  public int getDistributionInterval() {
+    return replicationConfig.getDistributionInterval();
+  }
+
+  @Override
   public String getVersion() {
     Hasher hasher = Hashing.murmur3_128().newHasher();
     hasher.putString(replicationConfig.getVersion(), UTF_8);
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/GerritRestApi.java b/src/main/java/com/googlesource/gerrit/plugins/replication/GerritRestApi.java
index 66130f9..fa81dd0 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/GerritRestApi.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/GerritRestApi.java
@@ -62,34 +62,34 @@
 
   @Override
   public boolean createProject(Project.NameKey project, String head) {
-    repLog.info("Creating project {} on {}", project, uri);
+    repLog.atInfo().log("Creating project %s on %s", project, uri);
     String url = String.format("%s/a/projects/%s", toHttpUri(uri), Url.encode(project.get()));
     try {
       return httpClient
           .execute(new HttpPut(url), new HttpResponseHandler(), getContext())
           .isSuccessful();
     } catch (IOException e) {
-      repLog.error("Couldn't perform project creation on {}", uri, e);
+      repLog.atSevere().withCause(e).log("Couldn't perform project creation on %s", uri);
       return false;
     }
   }
 
   @Override
   public boolean deleteProject(Project.NameKey project) {
-    repLog.info("Deleting project {} on {}", project, uri);
+    repLog.atInfo().log("Deleting project %s on %s", project, uri);
     String url = String.format("%s/a/projects/%s", toHttpUri(uri), Url.encode(project.get()));
     try {
       httpClient.execute(new HttpDelete(url), new HttpResponseHandler(), getContext());
       return true;
     } catch (IOException e) {
-      repLog.error("Couldn't perform project deletion on {}", uri, e);
+      repLog.atSevere().withCause(e).log("Couldn't perform project deletion on %s", uri);
     }
     return false;
   }
 
   @Override
   public boolean updateHead(Project.NameKey project, String newHead) {
-    repLog.info("Updating head of {} on {}", project, uri);
+    repLog.atInfo().log("Updating head of %s on %s", project, uri);
     String url = String.format("%s/a/projects/%s/HEAD", toHttpUri(uri), Url.encode(project.get()));
     try {
       HttpPut req = new HttpPut(url);
@@ -98,7 +98,7 @@
       httpClient.execute(req, new HttpResponseHandler(), getContext());
       return true;
     } catch (IOException e) {
-      repLog.error("Couldn't perform update head on {}", uri, e);
+      repLog.atSevere().withCause(e).log("Couldn't perform update head on %s", uri);
     }
     return false;
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/LocalFS.java b/src/main/java/com/googlesource/gerrit/plugins/replication/LocalFS.java
index da960e6..b092363 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/LocalFS.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/LocalFS.java
@@ -43,9 +43,9 @@
         u.disableRefLog();
         u.link(head);
       }
-      repLog.info("Created local repository: {}", uri);
+      repLog.atInfo().log("Created local repository: %s", uri);
     } catch (IOException e) {
-      repLog.error("Error creating local repository {}", uri.getPath(), e);
+      repLog.atSevere().withCause(e).log("Error creating local repository %s", uri.getPath());
       return false;
     }
     return true;
@@ -55,9 +55,9 @@
   public boolean deleteProject(Project.NameKey project) {
     try {
       recursivelyDelete(new File(uri.getPath()));
-      repLog.info("Deleted local repository: {}", uri);
+      repLog.atInfo().log("Deleted local repository: %s", uri);
     } catch (IOException e) {
-      repLog.error("Error deleting local repository {}:\n", uri.getPath(), e);
+      repLog.atSevere().withCause(e).log("Error deleting local repository %s:\n", uri.getPath());
       return false;
     }
     return true;
@@ -71,7 +71,8 @@
         u.link(newHead);
       }
     } catch (IOException e) {
-      repLog.error("Failed to update HEAD of repository {} to {}", uri.getPath(), newHead, e);
+      repLog.atSevere().withCause(e).log(
+          "Failed to update HEAD of repository %s to %s", uri.getPath(), newHead);
       return false;
     }
     return true;
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
index b5838e5..8322b2f 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
@@ -37,6 +37,7 @@
 import com.google.gerrit.server.git.ProjectRunnable;
 import com.google.gerrit.server.git.WorkQueue.CanceledWhileRunning;
 import com.google.gerrit.server.ioutil.HexFormat;
+import com.google.gerrit.server.logging.TraceContext;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackend.RefFilterOptions;
 import com.google.gerrit.server.permissions.PermissionBackendException;
@@ -56,6 +57,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 import org.eclipse.jgit.errors.NoRemoteRepositoryException;
@@ -76,7 +78,6 @@
 import org.eclipse.jgit.transport.RemoteRefUpdate;
 import org.eclipse.jgit.transport.Transport;
 import org.eclipse.jgit.transport.URIish;
-import org.slf4j.MDC;
 
 /**
  * A push to remote operation started by {@link GitReferenceUpdatedListener}.
@@ -87,7 +88,7 @@
 class PushOne implements ProjectRunnable, CanceledWhileRunning {
   private final ReplicationStateListener stateLog;
   static final String ALL_REFS = "..all..";
-  static final String ID_MDC_KEY = "pushOneId";
+  static final String ID_KEY = "pushOneId";
 
   interface Factory {
     PushOne create(Project.NameKey d, URIish u);
@@ -169,17 +170,16 @@
 
   @Override
   public void cancel() {
-    repLog.info("Replication [{}] to {} was canceled", HexFormat.fromInt(id), getURI());
+    repLog.atInfo().log("Replication [%s] to %s was canceled", HexFormat.fromInt(id), getURI());
     canceledByReplication();
     pool.pushWasCanceled(this);
   }
 
   @Override
   public void setCanceledWhileRunning() {
-    repLog.info(
-        "Replication [{}] to {} was canceled while being executed",
-        HexFormat.fromInt(id),
-        getURI());
+    repLog.atInfo().log(
+        "Replication [%s] to %s was canceled while being executed",
+        HexFormat.fromInt(id), getURI());
     canceledWhileRunning.set(true);
   }
 
@@ -234,9 +234,10 @@
     if (ALL_REFS.equals(ref)) {
       delta.clear();
       pushAllRefs = true;
-      repLog.trace("Added all refs for replication to {}", uri);
+      repLog.atFinest().log("Added all refs for replication to %s", uri);
     } else if (!pushAllRefs && delta.add(ref)) {
-      repLog.trace("Added ref {} for replication to {}", ref, uri);
+      delta.add(ref);
+      repLog.atFinest().log("Added ref %s for replication to %s", ref, uri);
     }
   }
 
@@ -313,28 +314,35 @@
   }
 
   private void runPushOperation() {
+    try (TraceContext ctx = TraceContext.open().addTag(ID_KEY, HexFormat.fromInt(id))) {
+      doRunPushOperation();
+    }
+  }
+
+  private void doRunPushOperation() {
     // Lock the queue, and remove ourselves, so we can't be modified once
     // we start replication (instead a new instance, with the same URI, is
     // created and scheduled for a future point in time.)
     //
-    MDC.put(ID_MDC_KEY, HexFormat.fromInt(id));
     RunwayStatus status = pool.requestRunway(this);
     isCollision = false;
     if (!status.isAllowed()) {
       if (status.isCanceled()) {
-        repLog.info("PushOp for replication to {} was canceled and thus won't be rescheduled", uri);
+        repLog.atInfo().log(
+            "PushOp for replication to %s was canceled and thus won't be rescheduled", uri);
+      } else if (status.isExternalInflight()) {
+        repLog.atInfo().log("PushOp for replication to %s was denied externally", uri);
       } else {
-        repLog.info(
-            "Rescheduling replication to {} to avoid collision with the in-flight push [{}].",
-            uri,
-            HexFormat.fromInt(status.getInFlightPushId()));
+        repLog.atInfo().log(
+            "Rescheduling replication to %s to avoid collision with the in-flight push [%s].",
+            uri, HexFormat.fromInt(status.getInFlightPushId()));
         pool.reschedule(this, Destination.RetryReason.COLLISION);
         isCollision = true;
       }
       return;
     }
 
-    repLog.info("Replication to {} started...", uri);
+    repLog.atInfo().log("Replication to %s started...", uri);
     Timer1.Context<String> destinationContext = metrics.start(config.getName());
     try {
       long startedAt = destinationContext.getStartTime();
@@ -348,12 +356,9 @@
         metrics.recordSlowProjectReplication(
             config.getName(), projectName.get(), pool.getSlowLatencyThreshold(), elapsed);
       }
-      repLog.info(
-          "Replication to {} completed in {}ms, {}ms delay, {} retries",
-          uri,
-          elapsed,
-          delay,
-          retryCount);
+      repLog.atInfo().log(
+          "Replication to %s completed in %dms, %dms delay, %d retries",
+          uri, elapsed, delay, retryCount);
     } catch (RepositoryNotFoundException e) {
       stateLog.error(
           "Cannot replicate " + projectName + "; Local repository error: " + e.getMessage(),
@@ -370,7 +375,7 @@
           || msg.contains("unavailable")) {
         createRepository();
       } else {
-        repLog.error("Cannot replicate {}; Remote repository error: {}", projectName, msg);
+        repLog.atSevere().log("Cannot replicate %s; Remote repository error: %s", projectName, msg);
       }
 
     } catch (NoRemoteRepositoryException e) {
@@ -380,10 +385,10 @@
     } catch (TransportException e) {
       Throwable cause = e.getCause();
       if (cause instanceof JSchException && cause.getMessage().startsWith("UnknownHostKey:")) {
-        repLog.error("Cannot replicate to {}: {}", uri, cause.getMessage());
+        repLog.atSevere().log("Cannot replicate to %s: %s", uri, cause.getMessage());
       } else if (e instanceof LockFailureException) {
         lockRetryCount++;
-        repLog.error("Cannot replicate to {} due to lock failure", uri);
+        repLog.atSevere().log("Cannot replicate to %s due to lock failure", uri);
 
         // The remote push operation should be retried.
         if (lockRetryCount <= maxLockRetries) {
@@ -393,14 +398,14 @@
             pool.reschedule(this, Destination.RetryReason.TRANSPORT_ERROR);
           }
         } else {
-          repLog.error(
-              "Giving up after {} lock failures during replication to {}", lockRetryCount, uri);
+          repLog.atSevere().log(
+              "Giving up after %d lock failures during replication to %s", lockRetryCount, uri);
         }
       } else {
         if (canceledWhileRunning.get()) {
           logCanceledWhileRunningException(e);
         } else {
-          repLog.error("Cannot replicate to {}", uri, e);
+          repLog.atSevere().withCause(e).log("Cannot replicate to %s", uri);
           // The remote push operation should be retried.
           pool.reschedule(this, Destination.RetryReason.TRANSPORT_ERROR);
         }
@@ -418,7 +423,7 @@
   }
 
   private void logCanceledWhileRunningException(TransportException e) {
-    repLog.info("Cannot replicate to {}. It was canceled while running", uri, e);
+    repLog.atInfo().withCause(e).log("Cannot replicate to %s. It was canceled while running", uri);
   }
 
   private void createRepository() {
@@ -426,10 +431,11 @@
       try {
         Ref head = git.exactRef(Constants.HEAD);
         if (createProject(projectName, head != null ? getName(head) : null)) {
-          repLog.warn("Missing repository created; retry replication to {}", uri);
+          repLog.atWarning().log("Missing repository created; retry replication to %s", uri);
           pool.reschedule(this, Destination.RetryReason.REPOSITORY_MISSING);
         } else {
-          repLog.warn("Missing repository could not be created when replicating {}", uri);
+          repLog.atWarning().log(
+              "Missing repository could not be created when replicating %s", uri);
         }
       } catch (IOException ioe) {
         stateLog.error(
@@ -476,10 +482,10 @@
     }
 
     if (replConfig.getMaxRefsToLog() == 0 || todo.size() <= replConfig.getMaxRefsToLog()) {
-      repLog.info("Push to {} references: {}", uri, refUpdatesForLogging(todo));
+      repLog.atInfo().log("Push to %s references: %s", uri, refUpdatesForLogging(todo));
     } else {
-      repLog.info(
-          "Push to {} references (first {} of {} listed): {}",
+      repLog.atInfo().log(
+          "Push to %s references (first %d of %d listed): %s",
           uri,
           replConfig.getMaxRefsToLog(),
           todo.size(),
@@ -518,8 +524,8 @@
 
   private List<RemoteRefUpdate> generateUpdates(Transport tn)
       throws IOException, PermissionBackendException {
-    ProjectState projectState = projectCache.checkedGet(projectName);
-    if (projectState == null) {
+    Optional<ProjectState> projectState = projectCache.get(projectName);
+    if (!projectState.isPresent()) {
       return Collections.emptyList();
     }
 
@@ -528,7 +534,7 @@
     boolean filter;
     PermissionBackend.ForProject forProject = permissionBackend.currentUser().project(projectName);
     try {
-      projectState.checkStatePermitsRead();
+      projectState.get().checkStatePermitsRead();
       forProject.check(ProjectPermission.READ);
       filter = false;
     } catch (AuthException | ResourceConflictException e) {
@@ -548,7 +554,11 @@
         }
         local = n;
       }
-      local = forProject.filter(local, git, RefFilterOptions.builder().setFilterMeta(true).build());
+      local =
+          forProject
+              .filter(local.values(), git, RefFilterOptions.builder().setFilterMeta(true).build())
+              .stream()
+              .collect(toMap(Ref::getName, r -> r));
     }
 
     List<RemoteRefUpdate> remoteUpdatesList =
@@ -565,7 +575,7 @@
     Map<String, Ref> remote = listRemote(tn);
     for (Ref src : local.values()) {
       if (!canPushRef(src.getName(), noPerms)) {
-        repLog.debug("Skipping push of ref {}", src.getName());
+        repLog.atFine().log("Skipping push of ref %s", src.getName());
         continue;
       }
 
@@ -582,7 +592,7 @@
     if (config.isMirror()) {
       for (Ref ref : remote.values()) {
         if (Constants.HEAD.equals(ref.getName())) {
-          repLog.debug("Skipping deletion of {}", ref.getName());
+          repLog.atFine().log("Skipping deletion of %s", ref.getName());
           continue;
         }
         RefSpec spec = matchDst(ref.getName());
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSsh.java b/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSsh.java
index 7538298..f96c157 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSsh.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSsh.java
@@ -42,17 +42,14 @@
     OutputStream errStream = sshHelper.newErrorBufferStream();
     try {
       sshHelper.executeRemoteSsh(uri, cmd, errStream);
-      repLog.info("Created remote repository: {}", uri);
+      repLog.atInfo().log("Created remote repository: %s", uri);
     } catch (IOException e) {
-      repLog.error(
-          "Error creating remote repository at {}:\n"
-              + "  Exception: {}\n"
-              + "  Command: {}\n"
-              + "  Output: {}",
-          uri,
-          e,
-          cmd,
-          errStream);
+      repLog.atSevere().log(
+          "Error creating remote repository at %s:\n"
+              + "  Exception: %s\n"
+              + "  Command: %s\n"
+              + "  Output: %s",
+          uri, e, cmd, errStream);
       return false;
     }
     return true;
@@ -65,17 +62,14 @@
     OutputStream errStream = sshHelper.newErrorBufferStream();
     try {
       sshHelper.executeRemoteSsh(uri, cmd, errStream);
-      repLog.info("Deleted remote repository: {}", uri);
+      repLog.atInfo().log("Deleted remote repository: %s", uri);
     } catch (IOException e) {
-      repLog.error(
-          "Error deleting remote repository at {}:\n"
-              + "  Exception: {}\n"
-              + "  Command: {}\n"
-              + "  Output: {}",
-          uri,
-          e,
-          cmd,
-          errStream);
+      repLog.atSevere().log(
+          "Error deleting remote repository at %s:\n"
+              + "  Exception: %s\n"
+              + "  Command: %s\n"
+              + "  Output: %s",
+          uri, e, cmd, errStream);
       return false;
     }
     return true;
@@ -90,16 +84,12 @@
     try {
       sshHelper.executeRemoteSsh(uri, cmd, errStream);
     } catch (IOException e) {
-      repLog.error(
-          "Error updating HEAD of remote repository at {} to {}:\n"
-              + "  Exception: {}\n"
-              + "  Command: {}\n"
-              + "  Output: {}",
-          uri,
-          newHead,
-          e,
-          cmd,
-          errStream);
+      repLog.atSevere().log(
+          "Error updating HEAD of remote repository at %s to %s:\n"
+              + "  Exception: %s\n"
+              + "  Command: %s\n"
+              + "  Output: %s",
+          uri, newHead, e, cmd, errStream);
       return false;
     }
     return true;
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationConfig.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationConfig.java
index d3d64db..99e5ee4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationConfig.java
@@ -45,6 +45,13 @@
   boolean isDefaultForceUpdate();
 
   /**
+   * Returns the interval in seconds for running task distribution.
+   *
+   * @return number of seconds, zero if never.
+   */
+  int getDistributionInterval();
+
+  /**
    * Returns the maximum number of ref-specs to log into the replication_log whenever a push
    * operation is completed against a replication end.
    *
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfig.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfig.java
index e99f6b1..2631cbe 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfig.java
@@ -47,9 +47,9 @@
     try {
       config.load();
     } catch (ConfigInvalidException e) {
-      repLog.error("Config file {} is invalid: {}", cfgPath, e.getMessage(), e);
+      repLog.atSevere().withCause(e).log("Config file %s is invalid: %s", cfgPath, e.getMessage());
     } catch (IOException e) {
-      repLog.error("Cannot read {}: {}", cfgPath, e.getMessage(), e);
+      repLog.atSevere().withCause(e).log("Cannot read %s: %s", cfgPath, e.getMessage());
     }
     this.replicateAllOnPluginStart = config.getBoolean("gerrit", "replicateOnStartup", false);
     this.defaultForceUpdate = config.getBoolean("gerrit", "defaultForceUpdate", false);
@@ -86,6 +86,11 @@
   }
 
   @Override
+  public int getDistributionInterval() {
+    return config.getInt("replication", "distributionInterval", 0);
+  }
+
+  @Override
   public int getMaxRefsToLog() {
     return maxRefsToLog;
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationLogFile.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationLogFile.java
index fed09f9..60a9523 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationLogFile.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationLogFile.java
@@ -28,6 +28,6 @@
         systemLog,
         serverInfo,
         ReplicationQueue.REPLICATION_LOG_NAME,
-        new PatternLayout("[%d] [%X{" + PushOne.ID_MDC_KEY + "}] %m%n"));
+        new PatternLayout("[%d] %m%n"));
   }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
index 869f728..a8ffeec 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
@@ -14,6 +14,8 @@
 
 package com.googlesource.gerrit.plugins.replication;
 
+import static java.util.concurrent.TimeUnit.SECONDS;
+
 import com.google.auto.value.AutoValue;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.Queues;
@@ -25,6 +27,7 @@
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.server.events.EventDispatcher;
 import com.google.gerrit.server.git.WorkQueue;
+import com.google.gerrit.util.logging.NamedFluentLogger;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.googlesource.gerrit.plugins.replication.PushResultProcessing.GitUpdateProcessing;
@@ -34,9 +37,9 @@
 import java.util.Optional;
 import java.util.Queue;
 import java.util.Set;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
 import org.eclipse.jgit.transport.URIish;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /** Manages automatic replication to remote repositories. */
 public class ReplicationQueue
@@ -46,10 +49,11 @@
         ProjectDeletedListener,
         HeadUpdatedListener {
   static final String REPLICATION_LOG_NAME = "replication_log";
-  static final Logger repLog = LoggerFactory.getLogger(REPLICATION_LOG_NAME);
+  static final NamedFluentLogger repLog = NamedFluentLogger.forName(REPLICATION_LOG_NAME);
 
   private final ReplicationStateListener stateLog;
 
+  private final ReplicationConfig replConfig;
   private final WorkQueue workQueue;
   private final DynamicItem<EventDispatcher> dispatcher;
   private final Provider<ReplicationDestinations> destinations; // For Guice circular dependency
@@ -57,14 +61,17 @@
   private volatile boolean running;
   private volatile boolean replaying;
   private final Queue<ReferenceUpdatedEvent> beforeStartupEventsQueue;
+  private Distributor distributor;
 
   @Inject
   ReplicationQueue(
+      ReplicationConfig rc,
       WorkQueue wq,
       Provider<ReplicationDestinations> rd,
       DynamicItem<EventDispatcher> dis,
       ReplicationStateListeners sl,
       ReplicationTasksStorage rts) {
+    replConfig = rc;
     workQueue = wq;
     dispatcher = dis;
     destinations = rd;
@@ -81,15 +88,17 @@
       replicationTasksStorage.resetAll();
       firePendingEvents();
       fireBeforeStartupEvents();
+      distributor = new Distributor(workQueue);
     }
   }
 
   @Override
   public void stop() {
     running = false;
+    distributor.stop();
     int discarded = destinations.get().shutdown();
     if (discarded > 0) {
-      repLog.warn("Canceled {} replication events during shutdown", discarded);
+      repLog.atWarning().log("Canceled %d replication events during shutdown", discarded);
     }
   }
 
@@ -110,17 +119,17 @@
   @VisibleForTesting
   public void scheduleFullSync(
       Project.NameKey project, String urlMatch, ReplicationState state, boolean now) {
-    fire(project, urlMatch, PushOne.ALL_REFS, state, now);
+    fire(project, urlMatch, PushOne.ALL_REFS, state, now, false);
   }
 
   @Override
   public void onGitReferenceUpdated(GitReferenceUpdatedListener.Event event) {
-    fire(event.getProjectName(), event.getRefName());
+    fire(event.getProjectName(), event.getRefName(), false);
   }
 
-  private void fire(String projectName, String refName) {
+  private void fire(String projectName, String refName, boolean isPersisted) {
     ReplicationState state = new ReplicationState(new GitUpdateProcessing(dispatcher.get()));
-    fire(Project.nameKey(projectName), null, refName, state, false);
+    fire(Project.nameKey(projectName), null, refName, state, false, isPersisted);
     state.markAllPushTasksScheduled();
   }
 
@@ -129,7 +138,8 @@
       String urlMatch,
       String refName,
       ReplicationState state,
-      boolean now) {
+      boolean now,
+      boolean isPersisted) {
     if (!running) {
       stateLog.warn(
           "Replication plugin did not finish startup before event, event replication is postponed",
@@ -141,12 +151,14 @@
     for (Destination cfg : destinations.get().getAll(FilterType.ALL)) {
       if (cfg.wouldPushProject(project) && cfg.wouldPushRef(refName)) {
         for (URIish uri : cfg.getURIs(project, urlMatch)) {
-          replicationTasksStorage.create(
-              new ReplicateRefUpdate(project.get(), refName, uri, cfg.getRemoteConfigName()));
+          if (!isPersisted) {
+            replicationTasksStorage.create(
+                new ReplicateRefUpdate(project.get(), refName, uri, cfg.getRemoteConfigName()));
+          }
           cfg.schedule(project, refName, uri, state, now);
         }
       } else {
-        repLog.debug("Skipping ref {} on project {}", refName, project.get());
+        repLog.atFine().log("Skipping ref %s on project %s", refName, project.get());
       }
     }
   }
@@ -159,8 +171,8 @@
       for (ReplicationTasksStorage.ReplicateRefUpdate t : replicationTasksStorage.listWaiting()) {
         String eventKey = String.format("%s:%s", t.project, t.ref);
         if (!eventsReplayed.contains(eventKey)) {
-          repLog.info("Firing pending task {}", eventKey);
-          fire(t.project, t.ref);
+          repLog.atInfo().log("Firing pending task %s", eventKey);
+          fire(t.project, t.ref, true);
           eventsReplayed.add(eventKey);
         }
       }
@@ -169,6 +181,30 @@
     }
   }
 
+  private void pruneCompleted() {
+    // Queue tasks have wrappers around them so workQueue.getTasks() does not return the PushOnes.
+    // We also cannot access them by taskId since PushOnes don't have a taskId, they do have
+    // and Id, but it not the id assigned to the task in the queues. The tasks in the queue
+    // do use the same name as returned by toString() though, so that be used to correlate
+    // PushOnes with queue tasks despite their wrappers.
+    Set<String> prunableTaskNames = new HashSet<>();
+    for (Destination destination : destinations.get().getAll(FilterType.ALL)) {
+      prunableTaskNames.addAll(destination.getPrunableTaskNames());
+    }
+
+    for (WorkQueue.Task<?> task : workQueue.getTasks()) {
+      WorkQueue.Task.State state = task.getState();
+      if (state == WorkQueue.Task.State.SLEEPING || state == WorkQueue.Task.State.READY) {
+        if (task instanceof WorkQueue.ProjectTask) {
+          if (prunableTaskNames.contains(task.toString())) {
+            repLog.atFine().log("Pruning externally completed task: %s", task);
+            task.cancel(false);
+          }
+        }
+      }
+    }
+  }
+
   @Override
   public void onProjectDeleted(ProjectDeletedListener.Event event) {
     Project.NameKey p = Project.nameKey(event.getProjectName());
@@ -188,8 +224,8 @@
     for (ReferenceUpdatedEvent event : beforeStartupEventsQueue) {
       String eventKey = String.format("%s:%s", event.projectName(), event.refName());
       if (!eventsReplayed.contains(eventKey)) {
-        repLog.info("Firing pending task {}", event);
-        fire(event.projectName(), event.refName());
+        repLog.atInfo().log("Firing pending task %s", event);
+        fire(event.projectName(), event.refName(), false);
         eventsReplayed.add(eventKey);
       }
     }
@@ -206,4 +242,49 @@
 
     public abstract String refName();
   }
+
+  protected class Distributor implements WorkQueue.CancelableRunnable {
+    public ScheduledThreadPoolExecutor executor;
+    public ScheduledFuture<?> future;
+
+    public Distributor(WorkQueue wq) {
+      int distributionInterval = replConfig.getDistributionInterval();
+      if (distributionInterval > 0) {
+        executor = wq.createQueue(1, "Replication Distribution", false);
+        future =
+            executor.scheduleWithFixedDelay(
+                this, distributionInterval, distributionInterval, SECONDS);
+      }
+    }
+
+    @Override
+    public void run() {
+      if (!running) {
+        return;
+      }
+      try {
+        firePendingEvents();
+        pruneCompleted();
+      } catch (Exception e) {
+        repLog.atSevere().withCause(e).log("error distributing tasks");
+      }
+    }
+
+    @Override
+    public void cancel() {
+      future.cancel(true);
+    }
+
+    public void stop() {
+      if (executor != null) {
+        cancel();
+        executor.getQueue().remove(this);
+      }
+    }
+
+    @Override
+    public String toString() {
+      return "Replication Distributor";
+    }
+  }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationStateLogger.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationStateLogger.java
index f2d55de..3e73033 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationStateLogger.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationStateLogger.java
@@ -31,19 +31,19 @@
   @Override
   public void warn(String msg, ReplicationState... states) {
     stateWriteErr("Warning: " + msg, states);
-    repLog.warn(msg);
+    repLog.atWarning().log(msg);
   }
 
   @Override
   public void error(String msg, ReplicationState... states) {
     stateWriteErr("Error: " + msg, states);
-    repLog.error(msg);
+    repLog.atSevere().log(msg);
   }
 
   @Override
   public void error(String msg, Throwable t, ReplicationState... states) {
     stateWriteErr("Error: " + msg, states);
-    repLog.error(msg, t);
+    repLog.atSevere().withCause(t).log(msg);
   }
 
   private void stateWriteErr(String msg, ReplicationState[] states) {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
index 8d4b10a..b805c72 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationTasksStorage.java
@@ -26,6 +26,7 @@
 import java.io.IOException;
 import java.nio.file.DirectoryIteratorException;
 import java.nio.file.DirectoryStream;
+import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
@@ -47,13 +48,19 @@
  * task:
  *
  * <p><code>
- *   .../building/<tmp_name>  new replication tasks under construction
- *   .../running/<sha1>       running replication tasks
- *   .../waiting/<sha1>       outstanding replication tasks
+ *   .../building/<tmp_name>                       new replication tasks under construction
+ *   .../running/<uri_sha1>/                       lock for URI
+ *   .../running/<uri_sha1>/<task_sha1>            running replication tasks
+ *   .../waiting/<task_sha1_NN_shard>/<task_sha1>  outstanding replication tasks
  * </code>
  *
+ * <p>The URI lock is acquired by creating the directory and released by removing it.
+ *
  * <p>Tasks are moved atomically via a rename between those directories to indicate the current
  * state of each task.
+ *
+ * <p>Note: The .../waiting/<task_sha1_NN_shard> directories are never removed. This helps prevent
+ * failures when moving tasks to and from the shard directories from different hosts concurrently.
  */
 @Singleton
 public class ReplicationTasksStorage {
@@ -61,26 +68,50 @@
 
   private boolean disableDeleteForTesting;
 
-  public static class ReplicateRefUpdate {
-    public final String project;
+  public static class ReplicateRefUpdate extends UriUpdate {
     public final String ref;
-    public final String uri;
-    public final String remote;
 
-    public ReplicateRefUpdate(PushOne push, String ref) {
-      this(push.getProjectNameKey().get(), ref, push.getURI(), push.getRemoteName());
+    public ReplicateRefUpdate(UriUpdate update, String ref) {
+      this(update.project, ref, update.uri, update.remote);
     }
 
     public ReplicateRefUpdate(String project, String ref, URIish uri, String remote) {
-      this.project = project;
+      this(project, ref, uri.toASCIIString(), remote);
+    }
+
+    protected ReplicateRefUpdate(String project, String ref, String uri, String remote) {
+      super(project, uri, remote);
       this.ref = ref;
-      this.uri = uri.toASCIIString();
+    }
+
+    @Override
+    public String toString() {
+      return "ref-update " + ref + " (" + super.toString() + ")";
+    }
+  }
+
+  public static class UriUpdate {
+    public final String project;
+    public final String uri;
+    public final String remote;
+
+    public UriUpdate(PushOne push) {
+      this(push.getProjectNameKey().get(), push.getURI(), push.getRemoteName());
+    }
+
+    public UriUpdate(String project, URIish uri, String remote) {
+      this(project, uri.toASCIIString(), remote);
+    }
+
+    public UriUpdate(String project, String uri, String remote) {
+      this.project = project;
+      this.uri = uri;
       this.remote = remote;
     }
 
     @Override
     public String toString() {
-      return "ref-update " + project + ":" + ref + " uri:" + uri + " remote:" + remote;
+      return "uri-update " + project + " uri:" + uri + " remote:" + remote;
     }
   }
 
@@ -108,28 +139,65 @@
     this.disableDeleteForTesting = deleteDisabled;
   }
 
-  public synchronized void start(PushOne push) {
-    for (String ref : push.getRefs()) {
-      new Task(new ReplicateRefUpdate(push, ref)).start();
+  public synchronized boolean start(PushOne push) {
+    UriLock lock = new UriLock(push);
+    if (!lock.acquire()) {
+      return false;
     }
+
+    boolean started = false;
+    for (String ref : push.getRefs()) {
+      started = new Task(lock, ref).start() || started;
+    }
+
+    if (!started) { // No tasks left, likely replicated externally
+      lock.release();
+    }
+    return started;
   }
 
   public synchronized void reset(PushOne push) {
+    UriLock lock = new UriLock(push);
     for (String ref : push.getRefs()) {
-      new Task(new ReplicateRefUpdate(push, ref)).reset();
+      new Task(lock, ref).reset();
     }
+    lock.release();
   }
 
   public synchronized void resetAll() {
-    for (ReplicateRefUpdate r : listRunning()) {
-      new Task(r).reset();
+    try (DirectoryStream<Path> dirs = Files.newDirectoryStream(createDir(runningUpdates))) {
+      for (Path dir : dirs) {
+        UriLock lock = null;
+        try {
+          for (ReplicateRefUpdate u : list(dir)) {
+            if (lock == null) {
+              lock = new UriLock(u);
+            }
+            new Task(u).reset();
+          }
+        } catch (DirectoryIteratorException d) {
+          // iterating over the sub-directories is expected to have dirs disappear
+          Nfs.throwIfNotStaleFileHandle(d.getCause());
+        }
+        if (lock != null) {
+          lock.release();
+        }
+      }
+    } catch (IOException e) {
+      logger.atSevere().withCause(e).log("Error while aborting running tasks");
     }
   }
 
-  public synchronized void finish(PushOne push) {
-    for (String ref : push.getRefs()) {
-      new Task(new ReplicateRefUpdate(push, ref)).finish();
+  public boolean isWaiting(PushOne push) {
+    return push.getRefs().stream().map(ref -> new Task(push, ref)).anyMatch(Task::isWaiting);
+  }
+
+  public void finish(PushOne push) {
+    UriLock lock = new UriLock(push);
+    for (ReplicateRefUpdate r : list(lock.runningDir)) {
+      new Task(lock, r.ref).finish();
     }
+    lock.release();
   }
 
   public synchronized List<ReplicateRefUpdate> listWaiting() {
@@ -186,20 +254,73 @@
     }
   }
 
+  private class UriLock {
+    public final UriUpdate update;
+    public final String uriKey;
+    public final Path runningDir;
+
+    public UriLock(PushOne push) {
+      this(new UriUpdate(push));
+    }
+
+    public UriLock(UriUpdate update) {
+      this.update = update;
+      uriKey = sha1(update.uri).name();
+      runningDir = createDir(runningUpdates).resolve(uriKey);
+    }
+
+    public boolean acquire() {
+      try {
+        logger.atFine().log("MKDIR %s %s", runningDir, updateLog());
+        Files.createDirectory(runningDir);
+        return true;
+      } catch (FileAlreadyExistsException e) {
+        return false; // already running, likely externally
+      } catch (IOException e) {
+        logger.atSevere().withCause(e).log("Error while starting uri %s", uriKey);
+        return true; // safer to risk a duplicate than to skip it
+      }
+    }
+
+    public void release() {
+      if (disableDeleteForTesting) {
+        logger.atFine().log("DELETE %s %s DISABLED", runningDir, updateLog());
+        return;
+      }
+
+      try {
+        logger.atFine().log("DELETE %s %s", runningDir, updateLog());
+        Files.delete(runningDir);
+      } catch (IOException e) {
+        logger.atSevere().withCause(e).log("Error while releasing uri %s", uriKey);
+      }
+    }
+
+    private String updateLog() {
+      return String.format("(%s => %s)", update.project, update.uri);
+    }
+  }
+
   private class Task {
     public final ReplicateRefUpdate update;
-    public final String json;
     public final String taskKey;
     public final Path running;
     public final Path waiting;
 
-    public Task(ReplicateRefUpdate update) {
-      this.update = update;
-      json = GSON.toJson(update) + "\n";
+    public Task(ReplicateRefUpdate r) {
+      this(new UriLock(r), r.ref);
+    }
+
+    public Task(PushOne push, String ref) {
+      this(new UriLock(push), ref);
+    }
+
+    public Task(UriLock lock, String ref) {
+      update = new ReplicateRefUpdate(lock.update, ref);
       String key = update.project + "\n" + update.ref + "\n" + update.uri + "\n" + update.remote;
       taskKey = sha1(key).name();
-      running = createDir(runningUpdates).resolve(taskKey);
-      waiting = createDir(waitingUpdates).resolve(taskKey);
+      running = lock.runningDir.resolve(taskKey);
+      waiting = createDir(waitingUpdates.resolve(taskKey.substring(0, 2))).resolve(taskKey);
     }
 
     public String create() {
@@ -207,6 +328,7 @@
         return taskKey;
       }
 
+      String json = GSON.toJson(update) + "\n";
       try {
         Path tmp = Files.createTempFile(createDir(buildingUpdates), taskKey, null);
         logger.atFine().log("CREATE %s %s", tmp, updateLog());
@@ -219,14 +341,19 @@
       return taskKey;
     }
 
-    public void start() {
+    public boolean start() {
       rename(waiting, running);
+      return Files.exists(running);
     }
 
     public void reset() {
       rename(running, waiting);
     }
 
+    public boolean isWaiting() {
+      return Files.exists(waiting);
+    }
+
     public void finish() {
       if (disableDeleteForTesting) {
         logger.atFine().log("DELETE %s %s DISABLED", running, updateLog());
@@ -237,7 +364,7 @@
         logger.atFine().log("DELETE %s %s", running, updateLog());
         Files.delete(running);
       } catch (IOException e) {
-        logger.atSevere().withCause(e).log("Error while deleting task %s", taskKey);
+        logger.atSevere().withCause(e).log("Error while finishing task %s", taskKey);
       }
     }
 
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/RunwayStatus.java b/src/main/java/com/googlesource/gerrit/plugins/replication/RunwayStatus.java
index bcb1e2f..f7071d8 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/RunwayStatus.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/RunwayStatus.java
@@ -27,6 +27,10 @@
     return new RunwayStatus(false, inFlightPushId);
   }
 
+  public static RunwayStatus deniedExternal() {
+    return new RunwayStatus(false, -1);
+  }
+
   private final boolean allowed;
   private final int inFlightPushId;
 
@@ -43,6 +47,10 @@
     return !allowed && inFlightPushId == 0;
   }
 
+  public boolean isExternalInflight() {
+    return !allowed && inFlightPushId == -1;
+  }
+
   public int getInFlightPushId() {
     return inFlightPushId;
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/UpdateHeadTask.java b/src/main/java/com/googlesource/gerrit/plugins/replication/UpdateHeadTask.java
index ffa6be1..fdbd5e7 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/UpdateHeadTask.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/UpdateHeadTask.java
@@ -58,7 +58,8 @@
       return;
     }
 
-    repLog.warn("Cannot update HEAD of project {} on remote site {}.", project, replicateURI);
+    repLog.atWarning().log(
+        "Cannot update HEAD of project %s on remote site %s.", project, replicateURI);
   }
 
   @Override
diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 0aad73b..fc3352d 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -94,6 +94,20 @@
 :	Timeout for SSH connections. If 0, there is no timeout and
         the client waits indefinitely. By default, 2 minutes.
 
+replication.distributionInterval
+:	Interval in seconds for running the replication distributor. When
+	run, the replication distributor will add all persisted waiting tasks
+	to the queue to ensure that externally loaded tasks are visible to
+	the current process. If zero, turn off the replication distributor. By
+	default, zero.
+
+	Turning this on is likely only useful when there are other processes
+	(such as other masters in the same cluster) writing to the same
+	persistence store. To ensure that updates are seen well before their
+	replicationDelay expires when the distributor is used, the recommended
+	value for this is approximately the smallest remote.NAME.replicationDelay
+	divided by 5.
+
 replication.lockErrorMaxRetries
 :	Number of times to retry a replication operation if a lock
 	error is detected.
diff --git a/src/test/java/com/googlesource/gerrit/plugins/replication/PushOneTest.java b/src/test/java/com/googlesource/gerrit/plugins/replication/PushOneTest.java
index c09fcd1..94f0dc4 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/replication/PushOneTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/replication/PushOneTest.java
@@ -41,6 +41,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -245,9 +246,9 @@
     return push;
   }
 
-  private void setupProjectCacheMock() throws IOException {
+  private void setupProjectCacheMock() {
     projectCacheMock = mock(ProjectCache.class);
-    when(projectCacheMock.checkedGet(projectNameKey)).thenReturn(projectStateMock);
+    when(projectCacheMock.get(projectNameKey)).thenReturn(Optional.of(projectStateMock));
   }
 
   private void setupTransportMock() throws NotSupportedException, TransportException {
diff --git a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfigTest.java b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfigTest.java
index efacae7..79b05cc 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfigTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationFileBasedConfigTest.java
@@ -65,4 +65,25 @@
     assertThatContainsDestination(destinations, remoteName1, remoteUrl1);
     assertThatContainsDestination(destinations, remoteName2, remoteUrl2);
   }
+
+  @Test
+  public void shouldSkipFetchRefSpecs() throws Exception {
+    FileBasedConfig config = newReplicationConfig();
+    String pushRemote = "pushRemote";
+    final String aRemoteURL = "ssh://somewhere/${name}.git";
+    config.setString("remote", pushRemote, "url", aRemoteURL);
+
+    String fetchRemote = "fetchRemote";
+    config.setString("remote", fetchRemote, "url", aRemoteURL);
+    config.setString("remote", fetchRemote, "fetch", "refs/*:refs/*");
+    config.save();
+
+    DestinationsCollection destinationsCollections =
+        newDestinationsCollections(newReplicationFileBasedConfig());
+    destinationsCollections.startup(workQueueMock);
+    List<Destination> destinations = destinationsCollections.getAll(FilterType.ALL);
+    assertThat(destinations).hasSize(1);
+
+    assertThatIsDestination(destinations.get(0), pushRemote, aRemoteURL);
+  }
 }