diff --git a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
index 9fc268281c..2b6f0aaacb 100644
--- a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
@@ -1,616 +1,626 @@
 <?php
 
 /**
  * @task discover   Discovering Repositories
  * @task svn        Discovering Subversion Repositories
  * @task git        Discovering Git Repositories
  * @task hg         Discovering Mercurial Repositories
  * @task internal   Internals
  */
 final class PhabricatorRepositoryDiscoveryEngine
   extends PhabricatorRepositoryEngine {
 
   private $repairMode;
   private $commitCache = array();
   private $workingSet = array();
 
   const MAX_COMMIT_CACHE_SIZE = 2048;
 
 
 /* -(  Discovering Repositories  )------------------------------------------- */
 
 
   public function setRepairMode($repair_mode) {
     $this->repairMode = $repair_mode;
     return $this;
   }
 
 
   public function getRepairMode() {
     return $this->repairMode;
   }
 
 
   /**
    * @task discovery
    */
   public function discoverCommits() {
     $repository = $this->getRepository();
 
     $vcs = $repository->getVersionControlSystem();
     switch ($vcs) {
       case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
         $refs = $this->discoverSubversionCommits();
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
         $refs = $this->discoverMercurialCommits();
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
         $refs = $this->discoverGitCommits();
         break;
       default:
         throw new Exception("Unknown VCS '{$vcs}'!");
     }
 
     // Clear the working set cache.
     $this->workingSet = array();
 
     // Record discovered commits and mark them in the cache.
     foreach ($refs as $ref) {
       $this->recordCommit(
         $repository,
         $ref->getIdentifier(),
         $ref->getEpoch(),
         $ref->getCanCloseImmediately());
 
       $this->commitCache[$ref->getIdentifier()] = true;
     }
 
     return $refs;
   }
 
 
 /* -(  Discovering Git Repositories  )--------------------------------------- */
 
 
   /**
    * @task git
    */
   private function discoverGitCommits() {
     $repository = $this->getRepository();
 
     if (!$repository->isHosted()) {
       $this->verifyGitOrigin($repository);
     }
 
     $branches = id(new DiffusionLowLevelGitRefQuery())
       ->setRepository($repository)
       ->withIsOriginBranch(true)
       ->execute();
 
     if (!$branches) {
       // This repository has no branches at all, so we don't need to do
       // anything. Generally, this means the repository is empty.
       return array();
     }
 
     $branches = $this->sortBranches($branches);
     $branches = mpull($branches, 'getCommitIdentifier', 'getShortName');
 
     $this->log(
       pht(
         'Discovering commits in repository %s.',
         $repository->getCallsign()));
 
+    $this->fillCommitCache(array_values($branches));
+
     $refs = array();
     foreach ($branches as $name => $commit) {
       $this->log(pht('Examining branch "%s", at "%s".', $name, $commit));
 
       if (!$repository->shouldTrackBranch($name)) {
         $this->log(pht("Skipping, branch is untracked."));
         continue;
       }
 
       if ($this->isKnownCommit($commit)) {
         $this->log(pht("Skipping, HEAD is known."));
         continue;
       }
 
       $this->log(pht("Looking for new commits."));
 
       $branch_refs = $this->discoverStreamAncestry(
         new PhabricatorGitGraphStream($repository, $commit),
         $commit,
         $repository->shouldAutocloseBranch($name));
 
       $this->didDiscoverRefs($branch_refs);
 
       $refs[] = $branch_refs;
     }
 
     return array_mergev($refs);
   }
 
 
   /**
    * Verify that the "origin" remote exists, and points at the correct URI.
    *
    * This catches or corrects some types of misconfiguration, and also repairs
    * an issue where Git 1.7.1 does not create an "origin" for `--bare` clones.
    * See T4041.
    *
    * @param   PhabricatorRepository Repository to verify.
    * @return  void
    */
   private function verifyGitOrigin(PhabricatorRepository $repository) {
     list($remotes) = $repository->execxLocalCommand(
       'remote show -n origin');
 
     $matches = null;
     if (!preg_match('/^\s*Fetch URL:\s*(.*?)\s*$/m', $remotes, $matches)) {
       throw new Exception(
         "Expected 'Fetch URL' in 'git remote show -n origin'.");
     }
 
     $remote_uri = $matches[1];
     $expect_remote = $repository->getRemoteURI();
 
     if ($remote_uri == "origin") {
       // If a remote does not exist, git pretends it does and prints out a
       // made up remote where the URI is the same as the remote name. This is
       // definitely not correct.
 
       // Possibly, we should use `git remote --verbose` instead, which does not
       // suffer from this problem (but is a little more complicated to parse).
       $valid = false;
       $exists = false;
     } else {
       $normal_type_git = PhabricatorRepositoryURINormalizer::TYPE_GIT;
 
       $remote_normal = id(new PhabricatorRepositoryURINormalizer(
         $normal_type_git,
         $remote_uri))->getNormalizedPath();
 
       $expect_normal = id(new PhabricatorRepositoryURINormalizer(
         $normal_type_git,
         $expect_remote))->getNormalizedPath();
 
       $valid = ($remote_normal == $expect_normal);
       $exists = true;
     }
 
     if (!$valid) {
       if (!$exists) {
         // If there's no "origin" remote, just create it regardless of how
         // strongly we own the working copy. There is almost no conceivable
         // scenario in which this could do damage.
         $this->log(
           pht(
             'Remote "origin" does not exist. Creating "origin", with '.
             'URI "%s".',
             $expect_remote));
         $repository->execxLocalCommand(
           'remote add origin %P',
           $repository->getRemoteURIEnvelope());
 
         // NOTE: This doesn't fetch the origin (it just creates it), so we won't
         // know about origin branches until the next "pull" happens. That's fine
         // for our purposes, but might impact things in the future.
       } else {
         if ($repository->canDestroyWorkingCopy()) {
           // Bad remote, but we can try to repair it.
           $this->log(
             pht(
               'Remote "origin" exists, but is pointed at the wrong URI, "%s". '.
               'Resetting origin URI to "%s.',
               $remote_uri,
               $expect_remote));
           $repository->execxLocalCommand(
             'remote set-url origin %P',
             $repository->getRemoteURIEnvelope());
         } else {
           // Bad remote and we aren't comfortable repairing it.
           $message = pht(
             'Working copy at "%s" has a mismatched origin URI, "%s". '.
             'The expected origin URI is "%s". Fix your configuration, or '.
             'set the remote URI correctly. To avoid breaking anything, '.
             'Phabricator will not automatically fix this.',
             $repository->getLocalPath(),
             $remote_uri,
             $expect_remote);
           throw new Exception($message);
         }
       }
     }
   }
 
 
 /* -(  Discovering Subversion Repositories  )-------------------------------- */
 
 
   /**
    * @task svn
    */
   private function discoverSubversionCommits() {
     $repository = $this->getRepository();
 
     if (!$repository->isHosted()) {
       $this->verifySubversionRoot($repository);
     }
 
     $upper_bound = null;
     $limit = 1;
     $refs = array();
     do {
       // Find all the unknown commits on this path. Note that we permit
       // importing an SVN subdirectory rather than the entire repository, so
       // commits may be nonsequential.
 
       if ($upper_bound === null) {
         $at_rev = 'HEAD';
       } else {
         $at_rev = ($upper_bound - 1);
       }
 
       try {
         list($xml, $stderr) = $repository->execxRemoteCommand(
           'log --xml --quiet --limit %d %s',
           $limit,
           $repository->getSubversionBaseURI($at_rev));
       } catch (CommandException $ex) {
         $stderr = $ex->getStdErr();
         if (preg_match('/(path|File) not found/', $stderr)) {
           // We've gone all the way back through history and this path was not
           // affected by earlier commits.
           break;
         }
         throw $ex;
       }
 
       $xml = phutil_utf8ize($xml);
       $log = new SimpleXMLElement($xml);
       foreach ($log->logentry as $entry) {
         $identifier = (int)$entry['revision'];
         $epoch = (int)strtotime((string)$entry->date[0]);
         $refs[$identifier] = id(new PhabricatorRepositoryCommitRef())
           ->setIdentifier($identifier)
           ->setEpoch($epoch)
           ->setCanCloseImmediately(true);
 
         if ($upper_bound === null) {
           $upper_bound = $identifier;
         } else {
           $upper_bound = min($upper_bound, $identifier);
         }
       }
 
       // Discover 2, 4, 8, ... 256 logs at a time. This allows us to initially
       // import large repositories fairly quickly, while pulling only as much
       // data as we need in the common case (when we've already imported the
       // repository and are just grabbing one commit at a time).
       $limit = min($limit * 2, 256);
 
     } while ($upper_bound > 1 && !$this->isKnownCommit($upper_bound));
 
     krsort($refs);
     while ($refs && $this->isKnownCommit(last($refs)->getIdentifier())) {
       array_pop($refs);
     }
     $refs = array_reverse($refs);
 
     $this->didDiscoverRefs($refs);
 
     return $refs;
   }
 
 
   private function verifySubversionRoot(PhabricatorRepository $repository) {
     list($xml) = $repository->execxRemoteCommand(
       'info --xml %s',
       $repository->getSubversionPathURI());
 
     $xml = phutil_utf8ize($xml);
     $xml = new SimpleXMLElement($xml);
 
     $remote_root = (string)($xml->entry[0]->repository[0]->root[0]);
     $expect_root = $repository->getSubversionPathURI();
 
     $normal_type_svn = PhabricatorRepositoryURINormalizer::TYPE_SVN;
 
     $remote_normal = id(new PhabricatorRepositoryURINormalizer(
       $normal_type_svn,
       $remote_root))->getNormalizedPath();
 
     $expect_normal = id(new PhabricatorRepositoryURINormalizer(
       $normal_type_svn,
       $expect_root))->getNormalizedPath();
 
     if ($remote_normal != $expect_normal) {
       throw new Exception(
         pht(
           'Repository "%s" does not have a correctly configured remote URI. '.
           'The remote URI for a Subversion repository MUST point at the '.
           'repository root. The root for this repository is "%s", but the '.
           'configured URI is "%s". To resolve this error, set the remote URI '.
           'to point at the repository root. If you want to import only part '.
           'of a Subversion repository, use the "Import Only" option.',
           $repository->getCallsign(),
           $remote_root,
           $expect_root));
     }
   }
 
 
 /* -(  Discovering Mercurial Repositories  )--------------------------------- */
 
 
   /**
    * @task hg
    */
   private function discoverMercurialCommits() {
     $repository = $this->getRepository();
 
     $branches = id(new DiffusionLowLevelMercurialBranchesQuery())
       ->setRepository($repository)
       ->execute();
 
+    $this->fillCommitCache(mpull($branches, 'getCommitIdentifier'));
+
     $refs = array();
     foreach ($branches as $branch) {
       // NOTE: Mercurial branches may have multiple heads, so the names may
       // not be unique.
       $name = $branch->getShortName();
       $commit = $branch->getCommitIdentifier();
 
       $this->log(pht('Examining branch "%s" head "%s".', $name, $commit));
       if (!$repository->shouldTrackBranch($name)) {
         $this->log(pht("Skipping, branch is untracked."));
         continue;
       }
 
       if ($this->isKnownCommit($commit)) {
         $this->log(pht("Skipping, this head is a known commit."));
         continue;
       }
 
       $this->log(pht("Looking for new commits."));
 
       $branch_refs = $this->discoverStreamAncestry(
         new PhabricatorMercurialGraphStream($repository, $commit),
         $commit,
         $close_immediately = true);
 
       $this->didDiscoverRefs($branch_refs);
 
       $refs[] = $branch_refs;
     }
 
     return array_mergev($refs);
   }
 
 
 /* -(  Internals  )---------------------------------------------------------- */
 
 
   private function discoverStreamAncestry(
     PhabricatorRepositoryGraphStream $stream,
     $commit,
     $close_immediately) {
 
     $discover = array($commit);
     $graph = array();
     $seen = array();
 
     // Find all the reachable, undiscovered commits. Build a graph of the
     // edges.
     while ($discover) {
       $target = array_pop($discover);
 
       if (empty($graph[$target])) {
         $graph[$target] = array();
       }
 
       $parents = $stream->getParents($target);
       foreach ($parents as $parent) {
         if ($this->isKnownCommit($parent)) {
           continue;
         }
 
         $graph[$target][$parent] = true;
 
         if (empty($seen[$parent])) {
           $seen[$parent] = true;
           $discover[] = $parent;
         }
       }
     }
 
     // Now, sort them topographically.
     $commits = $this->reduceGraph($graph);
 
     $refs = array();
     foreach ($commits as $commit) {
       $refs[] = id(new PhabricatorRepositoryCommitRef())
         ->setIdentifier($commit)
         ->setEpoch($stream->getCommitDate($commit))
         ->setCanCloseImmediately($close_immediately);
     }
 
     return $refs;
   }
 
 
   private function reduceGraph(array $edges) {
     foreach ($edges as $commit => $parents) {
       $edges[$commit] = array_keys($parents);
     }
 
     $graph = new PhutilDirectedScalarGraph();
     $graph->addNodes($edges);
 
     $commits = $graph->getTopographicallySortedNodes();
 
     // NOTE: We want the most ancestral nodes first, so we need to reverse the
     // list we get out of AbstractDirectedGraph.
     $commits = array_reverse($commits);
 
     return $commits;
   }
 
 
   private function isKnownCommit($identifier) {
     if (isset($this->commitCache[$identifier])) {
       return true;
     }
 
     if (isset($this->workingSet[$identifier])) {
       return true;
     }
 
     if ($this->repairMode) {
       // In repair mode, rediscover the entire repository, ignoring the
       // database state. We can hit the local cache above, but if we miss it
       // stop the script from going to the database cache.
       return false;
     }
 
-    $commit = id(new PhabricatorRepositoryCommit())->loadOneWhere(
-      'repositoryID = %d AND commitIdentifier = %s',
+    $this->fillCommitCache(array($identifier));
+
+    return isset($this->commitCache[$identifier]);
+  }
+
+  private function fillCommitCache(array $identifiers) {
+    if (!$identifiers) {
+      return;
+    }
+
+    $commits = id(new PhabricatorRepositoryCommit())->loadAllWhere(
+      'repositoryID = %d AND commitIdentifier IN (%Ls)',
       $this->getRepository()->getID(),
-      $identifier);
+      $identifiers);
 
-    if (!$commit) {
-      return false;
+    foreach ($commits as $commit) {
+      $this->commitCache[$commit->getCommitIdentifier()] = true;
     }
 
-    $this->commitCache[$identifier] = true;
     while (count($this->commitCache) > self::MAX_COMMIT_CACHE_SIZE) {
       array_shift($this->commitCache);
     }
-
-    return true;
   }
 
-
   /**
    * Sort branches so we process closeable branches first. This makes the
    * whole import process a little cheaper, since we can close these commits
    * the first time through rather than catching them in the refs step.
    *
    * @task internal
    *
    * @param   list<DiffusionRepositoryRef> List of branch heads.
    * @return  list<DiffusionRepositoryRef> Sorted list of branch heads.
    */
   private function sortBranches(array $branches) {
     $repository = $this->getRepository();
 
     $head_branches = array();
     $tail_branches = array();
     foreach ($branches as $branch) {
       $name = $branch->getShortName();
 
       if ($repository->shouldAutocloseBranch($name)) {
         $head_branches[] = $branch;
       } else {
         $tail_branches[] = $branch;
       }
     }
 
     return array_merge($head_branches, $tail_branches);
   }
 
 
   private function recordCommit(
     PhabricatorRepository $repository,
     $commit_identifier,
     $epoch,
     $close_immediately) {
 
     $commit = new PhabricatorRepositoryCommit();
     $commit->setRepositoryID($repository->getID());
     $commit->setCommitIdentifier($commit_identifier);
     $commit->setEpoch($epoch);
     if ($close_immediately) {
       $commit->setImportStatus(PhabricatorRepositoryCommit::IMPORTED_CLOSEABLE);
     }
 
     $data = new PhabricatorRepositoryCommitData();
 
     try {
       $commit->openTransaction();
         $commit->save();
         $data->setCommitID($commit->getID());
         $data->save();
       $commit->saveTransaction();
 
       $this->insertTask($repository, $commit);
 
       queryfx(
         $repository->establishConnection('w'),
         'INSERT INTO %T (repositoryID, size, lastCommitID, epoch)
           VALUES (%d, 1, %d, %d)
           ON DUPLICATE KEY UPDATE
             size = size + 1,
             lastCommitID =
               IF(VALUES(epoch) > epoch, VALUES(lastCommitID), lastCommitID),
             epoch = IF(VALUES(epoch) > epoch, VALUES(epoch), epoch)',
         PhabricatorRepository::TABLE_SUMMARY,
         $repository->getID(),
         $commit->getID(),
         $epoch);
 
       if ($this->repairMode) {
         // Normally, the query should throw a duplicate key exception. If we
         // reach this in repair mode, we've actually performed a repair.
         $this->log(pht('Repaired commit "%s".', $commit_identifier));
       }
 
       PhutilEventEngine::dispatchEvent(
         new PhabricatorEvent(
           PhabricatorEventType::TYPE_DIFFUSION_DIDDISCOVERCOMMIT,
           array(
             'repository'  => $repository,
             'commit'      => $commit,
           )));
 
     } catch (AphrontQueryDuplicateKeyException $ex) {
       $commit->killTransaction();
       // Ignore. This can happen because we discover the same new commit
       // more than once when looking at history, or because of races or
       // data inconsistency or cosmic radiation; in any case, we're still
       // in a good state if we ignore the failure.
     }
   }
 
   private function didDiscoverRefs(array $refs) {
     foreach ($refs as $ref) {
       $this->workingSet[$ref->getIdentifier()] = true;
     }
   }
 
   private function insertTask(
     PhabricatorRepository $repository,
     PhabricatorRepositoryCommit $commit,
     $data = array()) {
 
     $vcs = $repository->getVersionControlSystem();
     switch ($vcs) {
       case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
         $class = 'PhabricatorRepositoryGitCommitMessageParserWorker';
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
         $class = 'PhabricatorRepositorySvnCommitMessageParserWorker';
         break;
       case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
         $class = 'PhabricatorRepositoryMercurialCommitMessageParserWorker';
         break;
       default:
         throw new Exception("Unknown repository type '{$vcs}'!");
     }
 
     $data['commitID'] = $commit->getID();
 
     PhabricatorWorker::scheduleTask($class, $data);
   }
 
 }