diff --git a/resources/sql/autopatches/20180322.lock.01.identifier.sql b/resources/sql/autopatches/20180322.lock.01.identifier.sql
new file mode 100644
--- /dev/null
+++ b/resources/sql/autopatches/20180322.lock.01.identifier.sql
@@ -0,0 +1,5 @@
+ALTER TABLE {$NAMESPACE}_repository.repository_pushevent
+  ADD requestIdentifier VARBINARY(12);
+
+ALTER TABLE {$NAMESPACE}_repository.repository_pushevent
+  ADD UNIQUE KEY `key_request` (requestIdentifier);
diff --git a/scripts/repository/commit_hook.php b/scripts/repository/commit_hook.php
--- a/scripts/repository/commit_hook.php
+++ b/scripts/repository/commit_hook.php
@@ -187,6 +187,11 @@
   $engine->setRemoteProtocol($remote_protocol);
 }
 
+$request_identifier = getenv(DiffusionCommitHookEngine::ENV_REQUEST);
+if (strlen($request_identifier)) {
+  $engine->setRequestIdentifier($request_identifier);
+}
+
 try {
   $err = $engine->execute();
 } catch (DiffusionCommitHookRejectException $ex) {
diff --git a/scripts/ssh/ssh-exec.php b/scripts/ssh/ssh-exec.php
--- a/scripts/ssh/ssh-exec.php
+++ b/scripts/ssh/ssh-exec.php
@@ -8,6 +8,12 @@
 
 $ssh_log = PhabricatorSSHLog::getLog();
 
+$request_identifier = Filesystem::readRandomCharacters(12);
+$ssh_log->setData(
+  array(
+    'Q' => $request_identifier,
+  ));
+
 $args = new PhutilArgumentParser($argv);
 $args->setTagline(pht('execute SSH requests'));
 $args->setSynopsis(<<<EOSYNOPSIS
@@ -248,6 +254,7 @@
   $workflow->setSSHUser($user);
   $workflow->setOriginalArguments($original_argv);
   $workflow->setIsClusterRequest($is_cluster_request);
+  $workflow->setRequestIdentifier($request_identifier);
 
   $sock_stdin = fopen('php://stdin', 'r');
   if (!$sock_stdin) {
diff --git a/src/applications/config/option/PhabricatorAccessLogConfigOptions.php b/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
--- a/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
+++ b/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
@@ -47,6 +47,10 @@
       's' => pht('The system user.'),
       'S' => pht('The system sudo user.'),
       'k' => pht('ID of the SSH key used to authenticate the request.'),
+
+      // TODO: This is a reasonable thing to support in the HTTP access
+      // log, too.
+      'Q' => pht('A random, unique string which identifies the request.'),
     );
 
     $http_desc = pht(
diff --git a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
--- a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
+++ b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
@@ -12,6 +12,7 @@
 
   const ENV_REPOSITORY = 'PHABRICATOR_REPOSITORY';
   const ENV_USER = 'PHABRICATOR_USER';
+  const ENV_REQUEST = 'PHABRICATOR_REQUEST';
   const ENV_REMOTE_ADDRESS = 'PHABRICATOR_REMOTE_ADDRESS';
   const ENV_REMOTE_PROTOCOL = 'PHABRICATOR_REMOTE_PROTOCOL';
 
@@ -25,6 +26,7 @@
   private $subversionRepository;
   private $remoteAddress;
   private $remoteProtocol;
+  private $requestIdentifier;
   private $transactionKey;
   private $mercurialHook;
   private $mercurialCommits = array();
@@ -58,6 +60,15 @@
     return $this->remoteAddress;
   }
 
+  public function setRequestIdentifier($request_identifier) {
+    $this->requestIdentifier = $request_identifier;
+    return $this;
+  }
+
+  public function getRequestIdentifier() {
+    return $this->requestIdentifier;
+  }
+
   public function setSubversionTransactionInfo($transaction, $repository) {
     $this->subversionTransaction = $transaction;
     $this->subversionRepository = $repository;
@@ -620,6 +631,7 @@
     $env = array(
       self::ENV_REPOSITORY => $this->getRepository()->getPHID(),
       self::ENV_USER => $this->getViewer()->getUsername(),
+      self::ENV_REQUEST => $this->getRequestIdentifier(),
       self::ENV_REMOTE_PROTOCOL => $this->getRemoteProtocol(),
       self::ENV_REMOTE_ADDRESS => $this->getRemoteAddress(),
     );
@@ -1081,16 +1093,24 @@
       ->setDevicePHID($device_phid)
       ->setRepositoryPHID($this->getRepository()->getPHID())
       ->attachRepository($this->getRepository())
-      ->setEpoch(time());
+      ->setEpoch(PhabricatorTime::getNow());
   }
 
   private function newPushEvent() {
     $viewer = $this->getViewer();
-    return PhabricatorRepositoryPushEvent::initializeNewEvent($viewer)
+
+    $event = PhabricatorRepositoryPushEvent::initializeNewEvent($viewer)
       ->setRepositoryPHID($this->getRepository()->getPHID())
       ->setRemoteAddress($this->getRemoteAddress())
       ->setRemoteProtocol($this->getRemoteProtocol())
-      ->setEpoch(time());
+      ->setEpoch(PhabricatorTime::getNow());
+
+    $identifier = $this->getRequestIdentifier();
+    if (strlen($identifier)) {
+      $event->setRequestIdentifier($identifier);
+    }
+
+    return $event;
   }
 
   private function rejectEnormousChanges(array $content_updates) {
diff --git a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
@@ -30,6 +30,11 @@
       DiffusionCommitHookEngine::ENV_REMOTE_PROTOCOL => 'ssh',
     );
 
+    $identifier = $this->getRequestIdentifier();
+    if ($identifier !== null) {
+      $env[DiffusionCommitHookEngine::ENV_REQUEST] = $identifier;
+    }
+
     $remote_address = $this->getSSHRemoteAddress();
     if ($remote_address !== null) {
       $env[DiffusionCommitHookEngine::ENV_REMOTE_ADDRESS] = $remote_address;
diff --git a/src/applications/repository/query/PhabricatorRepositoryPushLogSearchEngine.php b/src/applications/repository/query/PhabricatorRepositoryPushLogSearchEngine.php
--- a/src/applications/repository/query/PhabricatorRepositoryPushLogSearchEngine.php
+++ b/src/applications/repository/query/PhabricatorRepositoryPushLogSearchEngine.php
@@ -101,6 +101,9 @@
       $fields[] = id(new PhabricatorIDExportField())
         ->setKey('pushID')
         ->setLabel(pht('Push ID')),
+      $fields[] = id(new PhabricatorStringExportField())
+        ->setKey('unique')
+        ->setLabel(pht('Unique')),
       $fields[] = id(new PhabricatorStringExportField())
         ->setKey('protocol')
         ->setLabel(pht('Protocol')),
@@ -209,6 +212,7 @@
 
       $map = array(
         'pushID' => $event->getID(),
+        'unique' => $event->getRequestIdentifier(),
         'protocol' => $event->getRemoteProtocol(),
         'repositoryPHID' => $repository_phid,
         'repository' => $repository_name,
diff --git a/src/applications/repository/storage/PhabricatorRepositoryPushEvent.php b/src/applications/repository/storage/PhabricatorRepositoryPushEvent.php
--- a/src/applications/repository/storage/PhabricatorRepositoryPushEvent.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryPushEvent.php
@@ -11,6 +11,7 @@
   protected $repositoryPHID;
   protected $epoch;
   protected $pusherPHID;
+  protected $requestIdentifier;
   protected $remoteAddress;
   protected $remoteProtocol;
   protected $rejectCode;
@@ -29,6 +30,7 @@
       self::CONFIG_AUX_PHID => true,
       self::CONFIG_TIMESTAMPS => false,
       self::CONFIG_COLUMN_SCHEMA => array(
+        'requestIdentifier' => 'bytes12?',
         'remoteAddress' => 'ipaddress?',
         'remoteProtocol' => 'text32?',
         'rejectCode' => 'uint32',
@@ -38,6 +40,10 @@
         'key_repository' => array(
           'columns' => array('repositoryPHID'),
         ),
+        'key_request' => array(
+          'columns' => array('requestIdentifier'),
+          'unique' => true,
+        ),
       ),
     ) + parent::getConfiguration();
   }
diff --git a/src/infrastructure/ssh/PhabricatorSSHWorkflow.php b/src/infrastructure/ssh/PhabricatorSSHWorkflow.php
--- a/src/infrastructure/ssh/PhabricatorSSHWorkflow.php
+++ b/src/infrastructure/ssh/PhabricatorSSHWorkflow.php
@@ -13,6 +13,7 @@
   private $errorChannel;
   private $isClusterRequest;
   private $originalArguments;
+  private $requestIdentifier;
 
   public function isExecutable() {
     return false;
@@ -89,6 +90,15 @@
     return $this->originalArguments;
   }
 
+  public function setRequestIdentifier($request_identifier) {
+    $this->requestIdentifier = $request_identifier;
+    return $this;
+  }
+
+  public function getRequestIdentifier() {
+    return $this->requestIdentifier;
+  }
+
   public function getSSHRemoteAddress() {
     $ssh_client = getenv('SSH_CLIENT');
     if (!strlen($ssh_client)) {