MC-37630: Updating Design Configuration runs full reindex which generates DDL statement DROP Table

Author: thiaramus

app/code/Magento/Theme/Model/Indexer/Design/IndexerHandler.php

@@ -0,0 +1,59 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+declare(strict_types=1);
+
+namespace Magento\Theme\Model\Indexer\Design;
+
+use Magento\Framework\App\ResourceConnection;
+use Magento\Framework\Indexer\IndexStructureInterface;
+use Magento\Framework\Indexer\SaveHandler\Batch;
+use Magento\Framework\Indexer\SaveHandler\Grid;
+use Magento\Framework\Indexer\ScopeResolver\FlatScopeResolver;
+use Magento\Framework\Indexer\ScopeResolver\IndexScopeResolver;
+
+class IndexerHandler extends Grid
+{
+    /**
+     * @var FlatScopeResolver
+     */
+    private $flatScopeResolver;
+
+    public function __construct(
+        IndexStructureInterface $indexStructure,
+        ResourceConnection $resource,
+        Batch $batch,
+        IndexScopeResolver $indexScopeResolver,
+        FlatScopeResolver $flatScopeResolver,
+        array $data,
+        $batchSize = 100)
+    {
+        parent::__construct(
+            $indexStructure,
+            $resource,
+            $batch,
+            $indexScopeResolver,
+            $flatScopeResolver,
+            $data,
+            $batchSize);
+
+        $this->flatScopeResolver = $flatScopeResolver;
+    }
+
+    /**
+     * Clean index table by truncation
+     *
+     * @inheritdoc
+     */
+    public function cleanIndex($dimensions)
+    {
+        $adapter = $this->resource->getConnection('write');
+        $tableName = $this->flatScopeResolver->resolve($this->getIndexName(), $dimensions);
+        if ($adapter->isTableExists($tableName)) {
+            $adapter->truncateTable($tableName);
+        }
+    }
+}

app/code/Magento/Theme/etc/indexer.xml

@@ -17,7 +17,7 @@
             <field name="store_group_id" xsi:type="filterable" dataType="int"/>
             <field name="store_id" xsi:type="filterable" dataType="int"/>
         </fieldset>
-        <saveHandler class="Magento\Framework\Indexer\SaveHandler\Grid"/>
+        <saveHandler class="Magento\Theme\Model\Indexer\Design\IndexerHandler"/>
         <structure class="Magento\Framework\Indexer\GridStructure"/>
     </indexer>
 </config>