Improve AdvancedPricingImportExport saving of bunch data

Current implementation inserts the same data from previous bunches again and again until the import finishes.
This might work in most cases because the insert checks for duplicates but causes problems for imports that do some pre-processing on the data before running the insert. This changes also significantly improves import performance.

Author: cebe

app/code/Magento/AdvancedPricingImportExport/Model/Import/AdvancedPricing.php

@@ -397,6 +397,7 @@ protected function saveAndReplaceAdvancedPrices()
         $listSku = [];
         $tierPrices = [];
         while ($bunch = $this->_dataSourceModel->getNextBunch()) {
+            $bunchTierPrices = [];
             foreach ($bunch as $rowNum => $rowData) {
                 if (!$this->validateRow($rowData, $rowNum)) {
                     $this->addRowError(ValidatorInterface::ERROR_SKU_IS_EMPTY, $rowNum);
@@ -410,7 +411,7 @@ protected function saveAndReplaceAdvancedPrices()
                 $rowSku = $rowData[self::COL_SKU];
                 $listSku[] = $rowSku;
                 if (!empty($rowData[self::COL_TIER_PRICE_WEBSITE])) {
-                    $tierPrices[$rowSku][] = [
+                    $tierPrice = [
                         'all_groups' => $rowData[self::COL_TIER_PRICE_CUSTOMER_GROUP] == self::VALUE_ALL_GROUPS,
                         'customer_group_id' => $this->getCustomerGroupId(
                             $rowData[self::COL_TIER_PRICE_CUSTOMER_GROUP]
@@ -422,17 +423,26 @@ protected function saveAndReplaceAdvancedPrices()
                             ? $rowData[self::COL_TIER_PRICE] : null,
                         'website_id' => $this->getWebSiteId($rowData[self::COL_TIER_PRICE_WEBSITE])
                     ];
+                    if (\Magento\ImportExport\Model\Import::BEHAVIOR_APPEND == $behavior) {
+                         $bunchTierPrices[$rowSku][] = $tierPrice;
+                    }
+                    if (\Magento\ImportExport\Model\Import::BEHAVIOR_REPLACE == $behavior) {
+                        $tierPrices[$rowSku][] = $tierPrice;
+                    }
                 }
             }
 
             if (\Magento\ImportExport\Model\Import::BEHAVIOR_APPEND == $behavior) {
-                $this->processCountExistingPrices($tierPrices, self::TABLE_TIER_PRICE)
-                    ->processCountNewPrices($tierPrices);
+                $this->processCountExistingPrices($bunchTierPrices, self::TABLE_TIER_PRICE)
+                    ->processCountNewPrices($bunchTierPrices);
 
-                $this->saveProductPrices($tierPrices, self::TABLE_TIER_PRICE);
-                if ($listSku) {
-                    $this->setUpdatedAt($listSku);
-                }
+                $this->saveProductPrices($bunchTierPrices, self::TABLE_TIER_PRICE);
+            }
+        }
+
+        if (\Magento\ImportExport\Model\Import::BEHAVIOR_APPEND == $behavior) {
+            if ($listSku) {
+                $this->setUpdatedAt($listSku);
             }
         }