ACP2E-3389: Adobe Commerce backend loads categories very slowly

Author: o-iegorov

app/code/Magento/Catalog/Model/ResourceModel/Category/Collection.php

@@ -337,10 +337,44 @@ public function loadProductCount($items, $countRegular = true, $countAnchor = tr
             $categoryIds = array_keys($anchor);
             $countSelect = $this->getProductsCountQuery($categoryIds, (bool)$websiteId);
             $categoryProductsCount = $this->_conn->fetchPairs($countSelect);
+
+            $subSelect = clone $this->_conn->select();
+            $subSelect->from(['ce2' => $this->getTable('catalog_category_entity')], 'ce2.entity_id')
+                ->where("ce2.path LIKE CONCAT(ce.path, '/%')");
+
+            $select = clone $this->_conn->select();
+            $select->from(['ce' => $this->getTable(
+                'catalog_category_entity')],
+                'ce.entity_id'
+            );
+            $joinCondition =  new \Zend_Db_Expr("ce.entity_id=cp.category_id OR cp.category_id IN ({$subSelect})");
+            $select->joinLeft([
+                'cp' => $this->getProductTable()],
+                $joinCondition,
+                'COUNT(DISTINCT cp.product_id) AS product_count'
+            );
+            if ($websiteId) {
+                $select->join(
+                    ['w' => $this->getProductWebsiteTable()],
+                    'cp.product_id = w.product_id',
+                    []
+                )->where(
+                    'w.website_id = ?',
+                    $websiteId
+                );
+            }
+            $select->where('ce.entity_id IN(?)', $categoryIds);
+            $select->group('ce.entity_id');
+
+            $countFromCategoryTable = $this->_conn->fetchPairs($select);
+
             foreach ($anchor as $item) {
-                $productsCount = isset($categoryProductsCount[$item->getId()])
-                    ? (int)$categoryProductsCount[$item->getId()]
-                    : $this->getProductsCountFromCategoryTable($item, $websiteId);
+                $productsCount = 0;
+                if (isset($categoryProductsCount[$item->getId()])) {
+                    $productsCount = (int)$categoryProductsCount[$item->getId()];
+                } elseif (isset($countFromCategoryTable[$item->getId()])) {
+                    $productsCount = (int)$countFromCategoryTable[$item->getId()];
+                }
                 $item->setProductCount($productsCount);
             }
         }