perf: Reduce GC pressure by avoiding EJSON.clone

lib/cache/ObservableCollection.js

@@ -196,11 +196,12 @@ export default class ObservableCollection {
      * @param safe {Boolean} If this is set to true, it assumes that the object is cleaned
      */
     add(doc, safe = false) {
-        doc = EJSON.clone(doc);
-
         if (!safe) {
             if (this.fieldsArray) {
+                // projection function clones the document already.
                 doc = this.projectFieldsOnDoc(doc);
+            } else {
+                doc = EJSON.clone(doc);
             }
         }
 

lib/mongo/ObserveMultiplex.js

@@ -41,6 +41,15 @@ export function ObserveMultiplexer(options) {
     });
 }
 
+function strictFreeze(obj) {
+    return new Proxy(obj, {
+        set() {
+            throw new Error('Cannot mutate a frozen object');
+        }
+    });
+}
+const freezeObject = Meteor.isProduction ? Object.freeze : strictFreeze
+
 Object.assign(ObserveMultiplexer.prototype, {
     addHandleAndSendInitialAdds: function(handle) {
         var self = this;
@@ -213,24 +222,25 @@ Object.assign(ObserveMultiplexer.prototype, {
             // can continue until these are done. (But we do have to be careful to not
             // use a handle that got removed, because removeHandle does not use the
             // queue; thus, we iterate over an array of keys that we control.)
+            const safeArgs = freezeObject(args);
+
             Object.keys(self._handles).forEach(function(handleId) {
                 var handle = self._handles && self._handles[handleId];
                 if (!handle) return;
                 var callback = handle['_' + callbackName];
-                // clone arguments so that callbacks can mutate their arguments
 
                 // We silence out removed exceptions
                 if (callback === 'removed') {
                     try {
-                        callback.apply(null, EJSON.clone(args));
+                        callback.apply(null, safeArgs);
                     } catch (e) {
                         // Supressing `removed non-existent exceptions`
                         if (!isRemovedNonExistent(e)) {
                             throw e;
                         }
                     }
                 } else {
-                    callback && callback.apply(null, EJSON.clone(args));
+                    callback && callback.apply(null, safeArgs);
                 }
             });
         });
@@ -250,8 +260,7 @@ Object.assign(ObserveMultiplexer.prototype, {
         self._cache.docs.forEach(function(doc, id) {
             if (!_.has(self._handles, handle._id))
                 throw Error('handle got removed before sending initial adds!');
-            var fields = EJSON.clone(doc);
-            delete fields._id;
+            const { _id, ...fields } = doc
             if (self._ordered) add(id, fields, null);
             // we're going in order, so add at end
             else add(id, fields);

package.js

@@ -1,6 +1,6 @@
 Package.describe({
     name: 'cultofcoders:redis-oplog',
-    version: '2.2.2',
+    version: '2.3.0',
     // Brief, one-line summary of the package.
     summary: "Replacement for Meteor's MongoDB oplog implementation",
     // URL to the Git repository containing the source code for this package.