From 11f1d884d08fd64b6a331bae6eedc56d8f7988aa Mon Sep 17 00:00:00 2001
From: Lucas Hansen <lucashansen@gmail.com>
Date: Fri, 6 Nov 2015 14:49:44 -0800
Subject: [PATCH] Added a minimongo optimization to avoid some unecessary
 clones

---
 packages/minimongo/minimongo.js | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/packages/minimongo/minimongo.js b/packages/minimongo/minimongo.js
index 236a759629..f5e9a08863 100644
--- a/packages/minimongo/minimongo.js
+++ b/packages/minimongo/minimongo.js
@@ -696,12 +696,33 @@ LocalCollection.prototype.update = function (selector, mod, options, callback) {
   // it. (We don't need to save the original results of paused queries because
   // they already have a resultsSnapshot and we won't be diffing in
   // _recomputeResults.)
-  var qidToOriginalResults = {};
+  var qidToOriginalResults = {},
+      docMap = {}, // We should only clone each document once, even if it appears in multiple queries
+      onlyIDQuery = _.size(selector) === 1 && _.isString(selector._id); // If the selector is just looking up a single _id, then we only need to clone that document
   _.each(self.queries, function (query, qid) {
     // XXX for now, skip/limit implies ordered observe, so query.results is
     // always an array
-    if ((query.cursor.skip || query.cursor.limit) && ! self.paused)
-      qidToOriginalResults[qid] = EJSON.clone(query.results);
+    if ((query.cursor.skip || query.cursor.limit) && ! self.paused) {
+
+      // This is to catch LocalCollection._IdMap
+      if (_.isUndefined(query.results.length)) {
+        qidToOriginalResults[qid] = EJSON.clone(query.results);
+        return;
+      }
+
+      qidToOriginalResults[qid] = query.results.map(function(result) {
+        if (_.isUndefined(result) || _.isUndefined(result._id))
+          return EJSON.clone(result);
+
+        if (!_.has(docMap, result._id)) {
+          docMap[result._id] = (onlyIDQuery && result._id === selector._id) 
+                                ? EJSON.clone(result) 
+                                : result;
+        }
+
+        return docMap[result._id];
+      });
+    }
   });
   var recomputeQids = {};