[21] tell mysql to ignore the sort index for search queries

lib/private/DB/QueryBuilder/QueryBuilder.php

@@ -1305,4 +1305,21 @@ public function quoteAlias($alias) {
 
 		return $this->helper->quoteColumnName($alias);
 	}
+
+	/**
+	 * Either appends to or replaces a single, generic query part.
+	 *
+	 * The available parts are: 'select', 'from', 'set', 'where',
+	 * 'groupBy', 'having' and 'orderBy'.
+	 *
+	 * @param string $sqlPartName
+	 * @param mixed  $sqlPart
+	 * @param bool   $append
+	 *
+	 * @return $this This QueryBuilder instance.
+	 */
+	public function add(string $sqlPartName, $sqlPart, bool $append = false) {
+		$this->queryBuilder->add($sqlPartName, $sqlPart, $append);
+		return $this;
+	}
 }

lib/private/Files/Cache/Cache.php

@@ -588,7 +588,7 @@ private function removeChildren(ICacheEntry $entry) {
 			$query = $this->getQueryBuilder();
 			$query->delete('filecache_extended')
 				->where($query->expr()->in('fileid', $query->createParameter('childIds')));
-			
+
 			foreach (array_chunk($childIds, 1000) as $childIdChunk) {
 				$query->setParameter('childIds', $childIdChunk, IQueryBuilder::PARAM_INT_ARRAY);
 				$query->execute();
@@ -791,7 +791,7 @@ public function search($pattern) {
 		}
 
 		$query = $this->getQueryBuilder();
-		$query->selectFileCache()
+		$query->selectFileCache('file', 'ignore index for order by (fs_mtime)')
 			->whereStorageId()
 			->andWhere($query->expr()->iLike('name', $query->createNamedParameter($pattern)));
 
@@ -848,7 +848,13 @@ public function searchByMime($mimetype) {
 	protected function buildSearchQuery(ISearchQuery $searchQuery): IQueryBuilder {
 		$builder = $this->getQueryBuilder();
 
-		$query = $builder->selectFileCache('file');
+		// mysql really likes to pick an index for sorting if it can't fully satisfy the where
+		// filter with an index, since search queries pretty much never are fully filtered by index
+		// mysql often picks an index for sorting instead of the *much* more useful index for filtering.
+		//
+		// To bypass this, we tell mysql explicitly not to use the mtime (the default order field) index,
+		// so it will instead pick an index that is actually useful.
+		$query = $builder->selectFileCache('file', 'ignore index for order by (fs_mtime)');
 
 		$query->whereStorageId();
 

lib/private/Files/Cache/CacheQueryBuilder.php

@@ -26,6 +26,7 @@
 
 namespace OC\Files\Cache;
 
+use Doctrine\DBAL\Platforms\MySQLPlatform;
 use OC\DB\QueryBuilder\QueryBuilder;
 use OC\SystemConfig;
 use OCP\DB\QueryBuilder\IQueryBuilder;
@@ -45,12 +46,24 @@ public function __construct(IDBConnection $connection, SystemConfig $systemConfi
 		$this->cache = $cache;
 	}
 
-	public function selectFileCache(string $alias = null) {
+	public function selectFileCache(string $alias = null, string $mysqlIndexHint = '') {
 		$name = $alias ? $alias : 'filecache';
 		$this->select("$name.fileid", 'storage', 'path', 'path_hash', "$name.parent", 'name', 'mimetype', 'mimepart', 'size', 'mtime',
 			'storage_mtime', 'encrypted', 'etag', 'permissions', 'checksum', 'metadata_etag', 'creation_time', 'upload_time')
-			->from('filecache', $name)
-			->leftJoin($name, 'filecache_extended', 'fe', $this->expr()->eq("$name.fileid", 'fe.fileid'));
+			->from('filecache', $name);
+		if ($mysqlIndexHint !== '' && $this->getConnection()->getDatabasePlatform() instanceof MySQLPlatform) {
+			$this->add('join', [
+				$this->quoteAlias($name) => [
+					// horrible query builder crimes to sneak in raw sql after the "FROM oc_filecache $name"
+					'joinType' => $mysqlIndexHint . ' left',
+					'joinTable' => $this->getTableName('filecache_extended'),
+					'joinAlias' => $this->quoteAlias('fe'),
+					'joinCondition' => $this->expr()->eq("$name.fileid", 'fe.fileid'),
+				],
+			], true);
+		} else {
+			$this->leftJoin($name, 'filecache_extended', 'fe', $this->expr()->eq("$name.fileid", 'fe.fileid'));
+		}
 
 		$this->alias = $name;