for the DB ot pick an index specify the object_type

[blizzz]

The indices in the comments DB include the whole object, consisting of a type and its ID. The queries did not take the type in account (well, not everywhere), which used some subqueries to run expensive without using the index.

Before:

+----+-------------+-------+------------+-------+-------------------------------------------------------------------------------------------------------------------+-----------------------+---------+-------+------+----------+-----------------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+-------------------------------------------------------------------------------------------------------------------+-----------------------+---------+-------+------+----------+-----------------------------------------------------------------+
| 1 | SIMPLE | f | NULL | ref | PRIMARY,fs_storage_path_hash,fs_parent_name_hash,fs_storage_mimetype,fs_storage_mimepart,fs_storage_size,fs_mtime | fs_parent_name_hash | 8 | const | 1 | 100.00 | Using index; Using temporary; Using filesort |
| 1 | SIMPLE | c | NULL | index | NULL | comments_object_index | 522 | NULL | 427 | 55.00 | Using where; Using index; Using join buffer (Block Nested Loop) |
| 1 | SIMPLE | m | NULL | ALL | NULL | NULL | NULL | NULL | 23 | 8.80 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+-------+-------------------------------------------------------------------------------------------------------------------+-----------------------+---------+-------+------+----------+-----------------------------------------------------------------+

Now

+----+-------------+-------+------------+------+-------------------------------------------------------------------------------------------------------------------+------------------------------+---------+-------------------------------+------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+-------------------------------------------------------------------------------------------------------------------+------------------------------+---------+-------------------------------+------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | f | NULL | ref | PRIMARY,fs_storage_path_hash,fs_parent_name_hash,fs_storage_mimetype,fs_storage_mimepart,fs_storage_size,fs_mtime | fs_parent_name_hash | 8 | const | 1 | 100.00 | Using where; Using index; Using temporary; Using filesort |
| 1 | SIMPLE | c | NULL | ref | comments_object_index | comments_object_index | 258 | const | 20 | 100.00 | Using where; Using index |
| 1 | SIMPLE | m | NULL | ref | comments_marker_object_index | comments_marker_object_index | 516 | const,nextcloud.c.object_id | 1 | 16.00 | Using where |
+----+-------------+-------+------------+------+-------------------------------------------------------------------------------------------------------------------+------------------------------+---------+-------------------------------+------+----------+-----------------------------------------------------------+

[ChristophWurst]

Makes sense! Good catch!

[blizzz]

/backport to stable18

[blizzz]

/backport to stable17

[blizzz]

/backport to stable16

[backportbot-nextcloud]

backport to stable18 in #19283

[backportbot-nextcloud]

backport to stable17 in #19284

[backportbot-nextcloud]

backport to stable16 in #19285