tell mysql to ignore the sort index for search queries

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.

Signed-off-by: Robin Appelman <robin@icewind.nl>

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/private/Files/Cache/Cache.php b/lib/private/Files/Cache/Cache.php
index ae707fb5b54..99be91f5d6b 100644
--- a/lib/private/Files/Cache/Cache.php
+++ b/lib/private/Files/Cache/Cache.php
@@ -840,7 +840,13 @@ class Cache implements ICache {
 	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();