diff --git a/src/applications/diffusion/query/blame/DiffusionBlameQuery.php b/src/applications/diffusion/query/blame/DiffusionBlameQuery.php
index 6d83020dd2..4d03b4a143 100644
--- a/src/applications/diffusion/query/blame/DiffusionBlameQuery.php
+++ b/src/applications/diffusion/query/blame/DiffusionBlameQuery.php
@@ -1,69 +1,180 @@
 <?php
 
 abstract class DiffusionBlameQuery extends DiffusionQuery {
 
   private $timeout;
   private $paths;
 
   public function setTimeout($timeout) {
     $this->timeout = $timeout;
     return $this;
   }
 
   public function getTimeout() {
     return $this->timeout;
   }
 
   public function setPaths(array $paths) {
     $this->paths = $paths;
     return $this;
   }
 
   public function getPaths() {
     return $this->paths;
   }
 
   abstract protected function newBlameFuture(DiffusionRequest $request, $path);
 
   abstract protected function resolveBlameFuture(ExecFuture $future);
 
   final public static function newFromDiffusionRequest(
     DiffusionRequest $request) {
     return parent::newQueryObject(__CLASS__, $request);
   }
 
   final protected function executeQuery() {
     $paths = $this->getPaths();
+
+    $blame = array();
+
+    // Load cache keys: these are the commits at which each path was last
+    // touched.
+    $keys = $this->loadCacheKeys($paths);
+
+    // Try to read blame data from cache.
+    $cache = $this->readCacheData($keys);
+    foreach ($paths as $key => $path) {
+      if (!isset($cache[$path])) {
+        continue;
+      }
+
+      $blame[$path] = $cache[$path];
+      unset($paths[$key]);
+    }
+
+    // If we have no paths left, we filled everything from cache and can
+    // bail out early.
+    if (!$paths) {
+      return $blame;
+    }
+
     $request = $this->getRequest();
     $timeout = $this->getTimeout();
 
+    // We're still missing at least some data, so we need to run VCS commands
+    // to pull it.
     $futures = array();
     foreach ($paths as $path) {
       $future = $this->newBlameFuture($request, $path);
 
       if ($timeout) {
         $future->setTimeout($timeout);
       }
 
       $futures[$path] = $future;
     }
 
+    $futures = id(new FutureIterator($futures))
+      ->limit(4);
 
-    $blame = array();
+    foreach ($futures as $path => $future) {
+      $path_blame = $this->resolveBlameFuture($future);
+      if ($path_blame !== null) {
+        $blame[$path] = $path_blame;
+      }
+    }
+
+    // Fill the cache with anything we generated.
+    $this->writeCacheData(
+      array_select_keys($keys, $paths),
+      $blame);
 
-    if ($futures) {
-      $futures = id(new FutureIterator($futures))
-        ->limit(4);
+    return $blame;
+  }
 
-      foreach ($futures as $path => $future) {
-        $path_blame = $this->resolveBlameFuture($future);
-        if ($path_blame !== null) {
-          $blame[$path] = $path_blame;
-        }
+  private function loadCacheKeys(array $paths) {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $repository = $request->getRepository();
+    $repository_id = $repository->getID();
+
+    $last_modified = parent::callConduitWithDiffusionRequest(
+      $viewer,
+      $request,
+      'diffusion.lastmodifiedquery',
+      array(
+        'paths' => array_fill_keys($paths, $request->getCommit()),
+      ));
+
+    $map = array();
+    foreach ($paths as $path) {
+      $identifier = idx($last_modified, $path);
+      if ($identifier === null) {
+        continue;
       }
+
+      $map[$path] = "blame({$repository_id}, {$identifier}, {$path}, raw)";
     }
 
-    return $blame;
+    return $map;
+  }
+
+  private function readCacheData(array $keys) {
+    $cache = PhabricatorCaches::getImmutableCache();
+    $data = $cache->getKeys($keys);
+
+    $results = array();
+    foreach ($keys as $path => $key) {
+      if (!isset($data[$key])) {
+        continue;
+      }
+      $results[$path] = $data[$key];
+    }
+
+    // Decode the cache storage format.
+    foreach ($results as $path => $cache) {
+      list($head, $body) = explode("\n", $cache, 2);
+      switch ($head) {
+        case 'raw':
+          $body = explode("\n", $body);
+          break;
+        default:
+          $body = null;
+          break;
+      }
+
+      if ($body === null) {
+        unset($results[$path]);
+      } else {
+        $results[$path] = $body;
+      }
+    }
+
+    return $results;
+  }
+
+  private function writeCacheData(array $keys, array $blame) {
+    $writes = array();
+    foreach ($keys as $path => $key) {
+      $value = idx($blame, $path);
+      if ($value === null) {
+        continue;
+      }
+
+      // For now, just store the entire value with a "raw" header. In the
+      // future, we could compress this or use IDs instead.
+      $value = "raw\n".implode("\n", $value);
+
+      $writes[$key] = $value;
+    }
+
+    if (!$writes) {
+      return;
+    }
+
+    $cache = PhabricatorCaches::getImmutableCache();
+    $data = $cache->setKeys($writes, phutil_units('14 days in seconds'));
   }
 
 }
diff --git a/src/applications/repository/query/PhabricatorRepositoryQuery.php b/src/applications/repository/query/PhabricatorRepositoryQuery.php
index 38fa5bf56c..bd9765130a 100644
--- a/src/applications/repository/query/PhabricatorRepositoryQuery.php
+++ b/src/applications/repository/query/PhabricatorRepositoryQuery.php
@@ -1,596 +1,598 @@
 <?php
 
 final class PhabricatorRepositoryQuery
   extends PhabricatorCursorPagedPolicyAwareQuery {
 
   private $ids;
   private $phids;
   private $callsigns;
   private $types;
   private $uuids;
   private $nameContains;
   private $remoteURIs;
   private $datasourceQuery;
 
   private $numericIdentifiers;
   private $callsignIdentifiers;
   private $phidIdentifiers;
   private $monogramIdentifiers;
 
   private $identifierMap;
 
   const STATUS_OPEN = 'status-open';
   const STATUS_CLOSED = 'status-closed';
   const STATUS_ALL = 'status-all';
   private $status = self::STATUS_ALL;
 
   const HOSTED_PHABRICATOR = 'hosted-phab';
   const HOSTED_REMOTE = 'hosted-remote';
   const HOSTED_ALL = 'hosted-all';
   private $hosted = self::HOSTED_ALL;
 
   private $needMostRecentCommits;
   private $needCommitCounts;
   private $needProjectPHIDs;
 
   public function withIDs(array $ids) {
     $this->ids = $ids;
     return $this;
   }
 
   public function withPHIDs(array $phids) {
     $this->phids = $phids;
     return $this;
   }
 
   public function withCallsigns(array $callsigns) {
     $this->callsigns = $callsigns;
     return $this;
   }
 
   public function withIdentifiers(array $identifiers) {
+    $identifiers = array_fuse($identifiers);
+
     $ids = array();
     $callsigns = array();
     $phids = array();
     $monograms = array();
 
     foreach ($identifiers as $identifier) {
       if (ctype_digit((string)$identifier)) {
         $ids[$identifier] = $identifier;
       } else if (preg_match('/^(r[A-Z]+)|(R[1-9]\d*)\z/', $identifier)) {
         $monograms[$identifier] = $identifier;
       } else {
         $repository_type = PhabricatorRepositoryRepositoryPHIDType::TYPECONST;
         if (phid_get_type($identifier) === $repository_type) {
           $phids[$identifier] = $identifier;
         } else {
           $callsigns[$identifier] = $identifier;
         }
       }
     }
 
     $this->numericIdentifiers = $ids;
     $this->callsignIdentifiers = $callsigns;
     $this->phidIdentifiers = $phids;
     $this->monogramIdentifiers = $monograms;
 
     return $this;
   }
 
   public function withStatus($status) {
     $this->status = $status;
     return $this;
   }
 
   public function withHosted($hosted) {
     $this->hosted = $hosted;
     return $this;
   }
 
   public function withTypes(array $types) {
     $this->types = $types;
     return $this;
   }
 
   public function withUUIDs(array $uuids) {
     $this->uuids = $uuids;
     return $this;
   }
 
   public function withNameContains($contains) {
     $this->nameContains = $contains;
     return $this;
   }
 
   public function withRemoteURIs(array $uris) {
     $this->remoteURIs = $uris;
     return $this;
   }
 
   public function withDatasourceQuery($query) {
     $this->datasourceQuery = $query;
     return $this;
   }
 
   public function needCommitCounts($need_counts) {
     $this->needCommitCounts = $need_counts;
     return $this;
   }
 
   public function needMostRecentCommits($need_commits) {
     $this->needMostRecentCommits = $need_commits;
     return $this;
   }
 
   public function needProjectPHIDs($need_phids) {
     $this->needProjectPHIDs = $need_phids;
     return $this;
   }
 
   public function getBuiltinOrders() {
     return array(
       'committed' => array(
         'vector' => array('committed', 'id'),
         'name' => pht('Most Recent Commit'),
       ),
       'name' => array(
         'vector' => array('name', 'id'),
         'name' => pht('Name'),
       ),
       'callsign' => array(
         'vector' => array('callsign'),
         'name' => pht('Callsign'),
       ),
       'size' => array(
         'vector' => array('size', 'id'),
         'name' => pht('Size'),
       ),
     ) + parent::getBuiltinOrders();
   }
 
   public function getIdentifierMap() {
     if ($this->identifierMap === null) {
       throw new PhutilInvalidStateException('execute');
     }
     return $this->identifierMap;
   }
 
   protected function willExecute() {
     $this->identifierMap = array();
   }
 
   public function newResultObject() {
     return new PhabricatorRepository();
   }
 
   protected function loadPage() {
     $table = $this->newResultObject();
     $data = $this->loadStandardPageRows($table);
     $repositories = $table->loadAllFromArray($data);
 
     if ($this->needCommitCounts) {
       $sizes = ipull($data, 'size', 'id');
       foreach ($repositories as $id => $repository) {
         $repository->attachCommitCount(nonempty($sizes[$id], 0));
       }
     }
 
     if ($this->needMostRecentCommits) {
       $commit_ids = ipull($data, 'lastCommitID', 'id');
       $commit_ids = array_filter($commit_ids);
       if ($commit_ids) {
         $commits = id(new DiffusionCommitQuery())
           ->setViewer($this->getViewer())
           ->withIDs($commit_ids)
           ->execute();
       } else {
         $commits = array();
       }
       foreach ($repositories as $id => $repository) {
         $commit = null;
         if (idx($commit_ids, $id)) {
           $commit = idx($commits, $commit_ids[$id]);
         }
         $repository->attachMostRecentCommit($commit);
       }
     }
 
     return $repositories;
   }
 
   protected function willFilterPage(array $repositories) {
     assert_instances_of($repositories, 'PhabricatorRepository');
 
     // TODO: Denormalize repository status into the PhabricatorRepository
     // table so we can do this filtering in the database.
     foreach ($repositories as $key => $repo) {
       $status = $this->status;
       switch ($status) {
         case self::STATUS_OPEN:
           if (!$repo->isTracked()) {
             unset($repositories[$key]);
           }
           break;
         case self::STATUS_CLOSED:
           if ($repo->isTracked()) {
             unset($repositories[$key]);
           }
           break;
         case self::STATUS_ALL:
           break;
         default:
           throw new Exception("Unknown status '{$status}'!");
       }
 
       // TODO: This should also be denormalized.
       $hosted = $this->hosted;
       switch ($hosted) {
         case self::HOSTED_PHABRICATOR:
           if (!$repo->isHosted()) {
             unset($repositories[$key]);
           }
           break;
         case self::HOSTED_REMOTE:
           if ($repo->isHosted()) {
             unset($repositories[$key]);
           }
           break;
         case self::HOSTED_ALL:
           break;
         default:
           throw new Exception(pht("Unknown hosted failed '%s'!", $hosted));
       }
     }
 
     // TODO: Denormalize this, too.
     if ($this->remoteURIs) {
       $try_uris = $this->getNormalizedPaths();
       $try_uris = array_fuse($try_uris);
       foreach ($repositories as $key => $repository) {
         if (!isset($try_uris[$repository->getNormalizedPath()])) {
           unset($repositories[$key]);
         }
       }
     }
 
     // Build the identifierMap
     if ($this->numericIdentifiers) {
       foreach ($this->numericIdentifiers as $id) {
         if (isset($repositories[$id])) {
           $this->identifierMap[$id] = $repositories[$id];
         }
       }
     }
 
     if ($this->callsignIdentifiers) {
       $repository_callsigns = mpull($repositories, null, 'getCallsign');
 
       foreach ($this->callsignIdentifiers as $callsign) {
         if (isset($repository_callsigns[$callsign])) {
           $this->identifierMap[$callsign] = $repository_callsigns[$callsign];
         }
       }
     }
 
     if ($this->phidIdentifiers) {
       $repository_phids = mpull($repositories, null, 'getPHID');
 
       foreach ($this->phidIdentifiers as $phid) {
         if (isset($repository_phids[$phid])) {
           $this->identifierMap[$phid] = $repository_phids[$phid];
         }
       }
     }
 
     if ($this->monogramIdentifiers) {
       $monogram_map = array();
       foreach ($repositories as $repository) {
         foreach ($repository->getAllMonograms() as $monogram) {
           $monogram_map[$monogram] = $repository;
         }
       }
 
       foreach ($this->monogramIdentifiers as $monogram) {
         if (isset($monogram_map[$monogram])) {
           $this->identifierMap[$monogram] = $monogram_map[$monogram];
         }
       }
     }
 
     return $repositories;
   }
 
   protected function didFilterPage(array $repositories) {
     if ($this->needProjectPHIDs) {
       $type_project = PhabricatorProjectObjectHasProjectEdgeType::EDGECONST;
 
       $edge_query = id(new PhabricatorEdgeQuery())
         ->withSourcePHIDs(mpull($repositories, 'getPHID'))
         ->withEdgeTypes(array($type_project));
       $edge_query->execute();
 
       foreach ($repositories as $repository) {
         $project_phids = $edge_query->getDestinationPHIDs(
           array(
             $repository->getPHID(),
           ));
         $repository->attachProjectPHIDs($project_phids);
       }
     }
 
     return $repositories;
   }
 
   protected function getPrimaryTableAlias() {
     return 'r';
   }
 
   public function getOrderableColumns() {
     return parent::getOrderableColumns() + array(
       'committed' => array(
         'table' => 's',
         'column' => 'epoch',
         'type' => 'int',
         'null' => 'tail',
       ),
       'callsign' => array(
         'table' => 'r',
         'column' => 'callsign',
         'type' => 'string',
         'unique' => true,
         'reverse' => true,
       ),
       'name' => array(
         'table' => 'r',
         'column' => 'name',
         'type' => 'string',
         'reverse' => true,
       ),
       'size' => array(
         'table' => 's',
         'column' => 'size',
         'type' => 'int',
         'null' => 'tail',
       ),
     );
   }
 
   protected function willExecuteCursorQuery(
     PhabricatorCursorPagedPolicyAwareQuery $query) {
     $vector = $this->getOrderVector();
 
     if ($vector->containsKey('committed')) {
       $query->needMostRecentCommits(true);
     }
 
     if ($vector->containsKey('size')) {
       $query->needCommitCounts(true);
     }
   }
 
   protected function getPagingValueMap($cursor, array $keys) {
     $repository = $this->loadCursorObject($cursor);
 
     $map = array(
       'id' => $repository->getID(),
       'callsign' => $repository->getCallsign(),
       'name' => $repository->getName(),
     );
 
     foreach ($keys as $key) {
       switch ($key) {
         case 'committed':
           $commit = $repository->getMostRecentCommit();
           if ($commit) {
             $map[$key] = $commit->getEpoch();
           } else {
             $map[$key] = null;
           }
           break;
         case 'size':
           $count = $repository->getCommitCount();
           if ($count) {
             $map[$key] = $count;
           } else {
             $map[$key] = null;
           }
           break;
       }
     }
 
     return $map;
   }
 
   protected function buildSelectClauseParts(AphrontDatabaseConnection $conn) {
     $parts = parent::buildSelectClauseParts($conn);
 
     if ($this->shouldJoinSummaryTable()) {
       $parts[] = 's.*';
     }
 
     return $parts;
   }
 
   protected function buildJoinClauseParts(AphrontDatabaseConnection $conn) {
     $joins = parent::buildJoinClauseParts($conn);
 
     if ($this->shouldJoinSummaryTable()) {
       $joins[] = qsprintf(
         $conn,
         'LEFT JOIN %T s ON r.id = s.repositoryID',
         PhabricatorRepository::TABLE_SUMMARY);
     }
 
     return $joins;
   }
 
   private function shouldJoinSummaryTable() {
     if ($this->needCommitCounts) {
       return true;
     }
 
     if ($this->needMostRecentCommits) {
       return true;
     }
 
     $vector = $this->getOrderVector();
     if ($vector->containsKey('committed')) {
       return true;
     }
 
     if ($vector->containsKey('size')) {
       return true;
     }
 
     return false;
   }
 
   protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
     $where = parent::buildWhereClauseParts($conn);
 
     if ($this->ids !== null) {
       $where[] = qsprintf(
         $conn,
         'r.id IN (%Ld)',
         $this->ids);
     }
 
     if ($this->phids !== null) {
       $where[] = qsprintf(
         $conn,
         'r.phid IN (%Ls)',
         $this->phids);
     }
 
     if ($this->callsigns !== null) {
       $where[] = qsprintf(
         $conn,
         'r.callsign IN (%Ls)',
         $this->callsigns);
     }
 
     if ($this->numericIdentifiers ||
       $this->callsignIdentifiers ||
       $this->phidIdentifiers ||
       $this->monogramIdentifiers) {
       $identifier_clause = array();
 
       if ($this->numericIdentifiers) {
         $identifier_clause[] = qsprintf(
           $conn,
           'r.id IN (%Ld)',
           $this->numericIdentifiers);
       }
 
       if ($this->callsignIdentifiers) {
         $identifier_clause[] = qsprintf(
           $conn,
           'r.callsign IN (%Ls)',
           $this->callsignIdentifiers);
       }
 
       if ($this->phidIdentifiers) {
         $identifier_clause[] = qsprintf(
           $conn,
           'r.phid IN (%Ls)',
           $this->phidIdentifiers);
       }
 
       if ($this->monogramIdentifiers) {
         $monogram_callsigns = array();
         $monogram_ids = array();
 
         foreach ($this->monogramIdentifiers as $identifier) {
           if ($identifier[0] == 'r') {
             $monogram_callsigns[] = substr($identifier, 1);
           } else {
             $monogram_ids[] = substr($identifier, 1);
           }
         }
 
         if ($monogram_ids) {
           $identifier_clause[] = qsprintf(
             $conn,
             'r.id IN (%Ld)',
             $monogram_ids);
         }
 
         if ($monogram_callsigns) {
           $identifier_clause[] = qsprintf(
             $conn,
             'r.callsign IN (%Ls)',
             $monogram_callsigns);
         }
       }
 
       $where = array('('.implode(' OR ', $identifier_clause).')');
     }
 
     if ($this->types) {
       $where[] = qsprintf(
         $conn,
         'r.versionControlSystem IN (%Ls)',
         $this->types);
     }
 
     if ($this->uuids) {
       $where[] = qsprintf(
         $conn,
         'r.uuid IN (%Ls)',
         $this->uuids);
     }
 
     if (strlen($this->nameContains)) {
       $where[] = qsprintf(
         $conn,
         'name LIKE %~',
         $this->nameContains);
     }
 
     if (strlen($this->datasourceQuery)) {
       // This handles having "rP" match callsigns starting with "P...".
       $query = trim($this->datasourceQuery);
       if (preg_match('/^r/', $query)) {
         $callsign = substr($query, 1);
       } else {
         $callsign = $query;
       }
       $where[] = qsprintf(
         $conn,
         'r.name LIKE %> OR r.callsign LIKE %>',
         $query,
         $callsign);
     }
 
     return $where;
   }
 
   public function getQueryApplicationClass() {
     return 'PhabricatorDiffusionApplication';
   }
 
   private function getNormalizedPaths() {
     $normalized_uris = array();
 
     // Since we don't know which type of repository this URI is in the general
     // case, just generate all the normalizations. We could refine this in some
     // cases: if the query specifies VCS types, or the URI is a git-style URI
     // or an `svn+ssh` URI, we could deduce how to normalize it. However, this
     // would be more complicated and it's not clear if it matters in practice.
 
     foreach ($this->remoteURIs as $uri) {
       $normalized_uris[] = new PhabricatorRepositoryURINormalizer(
         PhabricatorRepositoryURINormalizer::TYPE_GIT,
         $uri);
       $normalized_uris[] = new PhabricatorRepositoryURINormalizer(
         PhabricatorRepositoryURINormalizer::TYPE_SVN,
         $uri);
       $normalized_uris[] = new PhabricatorRepositoryURINormalizer(
         PhabricatorRepositoryURINormalizer::TYPE_MERCURIAL,
         $uri);
     }
 
     return array_unique(mpull($normalized_uris, 'getNormalizedPath'));
   }
 
 }