diff --git a/src/applications/transactions/engineextension/PhabricatorTransactionsFulltextEngineExtension.php b/src/applications/transactions/engineextension/PhabricatorTransactionsFulltextEngineExtension.php
--- a/src/applications/transactions/engineextension/PhabricatorTransactionsFulltextEngineExtension.php
+++ b/src/applications/transactions/engineextension/PhabricatorTransactionsFulltextEngineExtension.php
@@ -22,12 +22,28 @@
       return;
     }
 
-    $xactions = $query
+    $query
       ->setViewer($this->getViewer())
       ->withObjectPHIDs(array($object->getPHID()))
       ->withComments(true)
-      ->needComments(true)
-      ->execute();
+      ->needComments(true);
+
+    // See PHI719. Users occasionally create objects with huge numbers of
+    // comments, which can be slow to index. We handle this with reasonable
+    // grace: at time of writing, we can index a task with 100K comments in
+    // about 30 seconds. However, we do need to hold all the comments in
+    // memory in the AbstractDocument, so there's some practical limit to what
+    // we can realistically index.
+
+    // Since objects with more than 1,000 comments are not likely to be
+    // legitimate objects with actual discussion, index only the first
+    // thousand comments.
+
+    $query
+      ->setOrderVector(array('-id'))
+      ->setLimit(1000);
+
+    $xactions = $query->execute();
 
     foreach ($xactions as $xaction) {
       if (!$xaction->hasComment()) {