diff --git a/src/applications/conpherence/query/ConpherenceThreadQuery.php b/src/applications/conpherence/query/ConpherenceThreadQuery.php
index 7cb7003121..48dc3323e0 100644
--- a/src/applications/conpherence/query/ConpherenceThreadQuery.php
+++ b/src/applications/conpherence/query/ConpherenceThreadQuery.php
@@ -1,296 +1,335 @@
 <?php
 
 final class ConpherenceThreadQuery
   extends PhabricatorCursorPagedPolicyAwareQuery {
 
   const TRANSACTION_LIMIT = 100;
 
   private $phids;
   private $ids;
   private $participantPHIDs;
   private $needParticipants;
   private $needTransactions;
   private $needParticipantCache;
   private $afterTransactionID;
   private $beforeTransactionID;
   private $transactionLimit;
   private $fulltext;
   private $needProfileImage;
 
   public function needParticipantCache($participant_cache) {
     $this->needParticipantCache = $participant_cache;
     return $this;
   }
 
   public function needParticipants($need) {
     $this->needParticipants = $need;
     return $this;
   }
 
   public function needProfileImage($need) {
     $this->needProfileImage = $need;
     return $this;
   }
 
   public function needTransactions($need_transactions) {
     $this->needTransactions = $need_transactions;
     return $this;
   }
 
   public function withIDs(array $ids) {
     $this->ids = $ids;
     return $this;
   }
 
   public function withPHIDs(array $phids) {
     $this->phids = $phids;
     return $this;
   }
 
   public function withParticipantPHIDs(array $phids) {
     $this->participantPHIDs = $phids;
     return $this;
   }
 
   public function setAfterTransactionID($id) {
     $this->afterTransactionID = $id;
     return $this;
   }
 
   public function setBeforeTransactionID($id) {
     $this->beforeTransactionID = $id;
     return $this;
   }
 
   public function setTransactionLimit($transaction_limit) {
     $this->transactionLimit = $transaction_limit;
     return $this;
   }
 
   public function getTransactionLimit() {
     return $this->transactionLimit;
   }
 
   public function withFulltext($query) {
     $this->fulltext = $query;
     return $this;
   }
 
   public function withTitleNgrams($ngrams) {
     return $this->withNgramsConstraint(
       id(new ConpherenceThreadTitleNgrams()),
       $ngrams);
   }
 
   protected function loadPage() {
     $table = new ConpherenceThread();
     $conn_r = $table->establishConnection('r');
 
     $data = queryfx_all(
       $conn_r,
       'SELECT thread.* FROM %T thread %Q %Q %Q %Q %Q',
       $table->getTableName(),
       $this->buildJoinClause($conn_r),
       $this->buildWhereClause($conn_r),
       $this->buildGroupClause($conn_r),
       $this->buildOrderClause($conn_r),
       $this->buildLimitClause($conn_r));
 
     $conpherences = $table->loadAllFromArray($data);
 
     if ($conpherences) {
       $conpherences = mpull($conpherences, null, 'getPHID');
       $this->loadParticipantsAndInitHandles($conpherences);
       if ($this->needParticipantCache) {
         $this->loadCoreHandles($conpherences, 'getRecentParticipantPHIDs');
       }
       if ($this->needParticipants) {
         $this->loadCoreHandles($conpherences, 'getParticipantPHIDs');
       }
       if ($this->needTransactions) {
         $this->loadTransactionsAndHandles($conpherences);
       }
       if ($this->needProfileImage) {
         $default = null;
         $file_phids = mpull($conpherences, 'getProfileImagePHID');
         $file_phids = array_filter($file_phids);
         if ($file_phids) {
           $files = id(new PhabricatorFileQuery())
             ->setParentQuery($this)
             ->setViewer($this->getViewer())
             ->withPHIDs($file_phids)
             ->execute();
           $files = mpull($files, null, 'getPHID');
         } else {
           $files = array();
         }
 
         foreach ($conpherences as $conpherence) {
           $file = idx($files, $conpherence->getProfileImagePHID());
           if (!$file) {
             if (!$default) {
               $default = PhabricatorFile::loadBuiltin(
                 $this->getViewer(),
                 'conpherence.png');
             }
             $file = $default;
           }
           $conpherence->attachProfileImageFile($file);
         }
       }
     }
 
     return $conpherences;
   }
 
   protected function buildGroupClause(AphrontDatabaseConnection $conn_r) {
     if ($this->participantPHIDs !== null || strlen($this->fulltext)) {
       return 'GROUP BY thread.id';
     } else {
       return $this->buildApplicationSearchGroupClause($conn_r);
     }
   }
 
-  protected function buildJoinClause(AphrontDatabaseConnection $conn_r) {
-    $joins = array();
+  protected function buildJoinClauseParts(AphrontDatabaseConnection $conn) {
+    $joins = parent::buildJoinClauseParts($conn);
 
     if ($this->participantPHIDs !== null) {
       $joins[] = qsprintf(
-        $conn_r,
+        $conn,
         'JOIN %T p ON p.conpherencePHID = thread.phid',
         id(new ConpherenceParticipant())->getTableName());
     }
 
     if (strlen($this->fulltext)) {
       $joins[] = qsprintf(
-        $conn_r,
+        $conn,
         'JOIN %T idx ON idx.threadPHID = thread.phid',
         id(new ConpherenceIndex())->getTableName());
     }
 
-    $joins[] = $this->buildApplicationSearchJoinClause($conn_r);
-    return implode(' ', $joins);
+    // See note in buildWhereClauseParts() about this optimization.
+    $viewer = $this->getViewer();
+    if (!$viewer->isOmnipotent() && $viewer->isLoggedIn()) {
+      $joins[] = qsprintf(
+        $conn,
+        'LEFT JOIN %T vp ON vp.conpherencePHID = thread.phid
+          AND vp.participantPHID = %s',
+        id(new ConpherenceParticipant())->getTableName(),
+        $viewer->getPHID());
+    }
+
+    return $joins;
   }
 
-  protected function buildWhereClause(AphrontDatabaseConnection $conn_r) {
-    $where = array();
+  protected function buildWhereClauseParts(AphrontDatabaseConnection $conn) {
+    $where = parent::buildWhereClauseParts($conn);
 
-    $where[] = $this->buildPagingClause($conn_r);
+    // Optimize policy filtering of private rooms. If we are not looking for
+    // particular rooms by ID or PHID, we can just skip over any rooms with
+    // "View Policy: Room Participants" if the viewer isn't a participant: we
+    // know they won't be able to see the room.
+    // This avoids overheating browse/search queries, since it's common for
+    // a large number of rooms to be private and have this view policy.
+    $viewer = $this->getViewer();
+
+    $can_optimize =
+      !$viewer->isOmnipotent() &&
+      ($this->ids === null) &&
+      ($this->phids === null);
+
+    if ($can_optimize) {
+      $members_policy = id(new ConpherenceThreadMembersPolicyRule())
+        ->getObjectPolicyFullKey();
+
+      if ($viewer->isLoggedIn()) {
+        $where[] = qsprintf(
+          $conn,
+          'thread.viewPolicy != %s OR vp.participantPHID = %s',
+          $members_policy,
+          $viewer->getPHID());
+      } else {
+        $where[] = qsprintf(
+          $conn,
+          'thread.viewPolicy != %s',
+          $members_policy);
+      }
+    }
 
     if ($this->ids !== null) {
       $where[] = qsprintf(
-        $conn_r,
+        $conn,
         'thread.id IN (%Ld)',
         $this->ids);
     }
 
     if ($this->phids !== null) {
       $where[] = qsprintf(
-        $conn_r,
+        $conn,
         'thread.phid IN (%Ls)',
         $this->phids);
     }
 
     if ($this->participantPHIDs !== null) {
       $where[] = qsprintf(
-        $conn_r,
+        $conn,
         'p.participantPHID IN (%Ls)',
         $this->participantPHIDs);
     }
 
     if (strlen($this->fulltext)) {
       $where[] = qsprintf(
-        $conn_r,
+        $conn,
         'MATCH(idx.corpus) AGAINST (%s IN BOOLEAN MODE)',
         $this->fulltext);
     }
 
-    return $this->formatWhereClause($where);
+    return $where;
   }
 
   private function loadParticipantsAndInitHandles(array $conpherences) {
     $participants = id(new ConpherenceParticipant())
       ->loadAllWhere('conpherencePHID IN (%Ls)', array_keys($conpherences));
     $map = mgroup($participants, 'getConpherencePHID');
 
     foreach ($conpherences as $current_conpherence) {
       $conpherence_phid = $current_conpherence->getPHID();
 
       $conpherence_participants = idx(
         $map,
         $conpherence_phid,
         array());
 
       $conpherence_participants = mpull(
         $conpherence_participants,
         null,
         'getParticipantPHID');
 
       $current_conpherence->attachParticipants($conpherence_participants);
       $current_conpherence->attachHandles(array());
     }
 
     return $this;
   }
 
   private function loadCoreHandles(
     array $conpherences,
     $method) {
 
     $handle_phids = array();
     foreach ($conpherences as $conpherence) {
       $handle_phids[$conpherence->getPHID()] =
         $conpherence->$method();
     }
     $flat_phids = array_mergev($handle_phids);
     $viewer = $this->getViewer();
     $handles = $viewer->loadHandles($flat_phids);
     $handles = iterator_to_array($handles);
     foreach ($handle_phids as $conpherence_phid => $phids) {
       $conpherence = $conpherences[$conpherence_phid];
       $conpherence->attachHandles(
         $conpherence->getHandles() + array_select_keys($handles, $phids));
     }
     return $this;
   }
 
   private function loadTransactionsAndHandles(array $conpherences) {
     $query = id(new ConpherenceTransactionQuery())
       ->setViewer($this->getViewer())
       ->withObjectPHIDs(array_keys($conpherences))
       ->needHandles(true);
 
     // We have to flip these for the underyling query class. The semantics of
     // paging are tricky business.
     if ($this->afterTransactionID) {
       $query->setBeforeID($this->afterTransactionID);
     } else if ($this->beforeTransactionID) {
       $query->setAfterID($this->beforeTransactionID);
     }
     if ($this->getTransactionLimit()) {
       // fetch an extra for "show older" scenarios
       $query->setLimit($this->getTransactionLimit() + 1);
     }
     $transactions = $query->execute();
     $transactions = mgroup($transactions, 'getObjectPHID');
     foreach ($conpherences as $phid => $conpherence) {
       $current_transactions = idx($transactions, $phid, array());
       $handles = array();
       foreach ($current_transactions as $transaction) {
         $handles += $transaction->getHandles();
       }
       $conpherence->attachHandles($conpherence->getHandles() + $handles);
       $conpherence->attachTransactions($current_transactions);
     }
     return $this;
   }
 
   public function getQueryApplicationClass() {
     return 'PhabricatorConpherenceApplication';
   }
 
   protected function getPrimaryTableAlias() {
     return 'thread';
   }
 
 }