diff --git a/imports/reactiveCache.js b/imports/reactiveCache.js
index 4674e9485..e6ea29439 100644
--- a/imports/reactiveCache.js
+++ b/imports/reactiveCache.js
@@ -1084,4 +1084,30 @@ ReactiveCache = {
   },
 }
 
-export { ReactiveCache };
+// Client side little MiniMongo DB "Index"
+ReactiveMiniMongoIndex = {
+  getSubTasksWithParentId(parentId, addSelect = {}, options) {
+    let ret = []
+    if (parentId) {
+      const select = {addSelect, options}
+      if (!this.__subTasksWithId) {
+        this.__subTasksWithId = new DataCache(_select => {
+          const __select = Jsons.parse(_select);
+          const _subTasks = ReactiveCache.getCards(
+            { parentId: { $exists: true },
+              ...__select.addSelect,
+            }, __select.options);
+          const _ret = _.groupBy(_subTasks, 'parentId')
+          return _ret;
+        });
+      }
+      ret = this.__subTasksWithId.get(Jsons.stringify(select));
+      if (ret) {
+        ret = ret[parentId] || [];
+      }
+    }
+    return ret;
+  }
+}
+
+export { ReactiveCache, ReactiveMiniMongoIndex };
diff --git a/models/cards.js b/models/cards.js
index 8cc5968e2..5e5f50f39 100644
--- a/models/cards.js
+++ b/models/cards.js
@@ -1,4 +1,4 @@
-import { ReactiveCache } from '/imports/reactiveCache';
+import { ReactiveCache, ReactiveMiniMongoIndex } from '/imports/reactiveCache';
 import moment from 'moment/min/moment-with-locales';
 import {
   ALLOWED_COLORS,
@@ -861,12 +861,9 @@ Cards.helpers({
   },
 
   subtasks() {
-    const ret = ReactiveCache.getCards(
-      {
-        parentId: this._id,
+    const ret = ReactiveMiniMongoIndex.getSubTasksWithParentId(this._id, {
         archived: false,
-      },
-      {
+      }, {
         sort: {
           sort: 1,
         },
@@ -876,17 +873,14 @@ Cards.helpers({
   },
 
   subtasksFinished() {
-    const ret = ReactiveCache.getCards({
-      parentId: this._id,
+    const ret = ReactiveMiniMongoIndex.getSubTasksWithParentId(this._id, {
       archived: true,
     });
     return ret;
   },
 
   allSubtasks() {
-    const ret = ReactiveCache.getCards({
-      parentId: this._id,
-    });
+    const ret = ReactiveMiniMongoIndex.getSubTasksWithParentId(this._id);
     return ret;
   },