Use storage filter when fetching previews to cleanup

[juliusknorr]

First attempt to speed up the slow query that is used to cleaning up previews a bit as described in #28114 in order to at least use the indexed storage column which would always be the root storage where the app data is located

The query is still quite bad with larger amounts of previews, but I don't see any further way to improve that other than basically moving back the preview cleanup to the actual deletion of files which of course would bring back the risk of timing out requests as described in 3e07c4f

I'll put some further ideas into #28114

[kesselb]

LGTM 👍

With storage id fs_storage_mimetype index is used on my setup.

[skjnldsv]

ready when you are @juliushaertl

[juliusknorr]

Did another check and this also seems to resolve #28114 where then the partial path index fs_storage_path_prefix is being used:

EXPLAIN SELECT `a`.`name` FROM `oc_filecache` `a` LEFT JOIN `oc_filecache` `b` ON `a`.`name` = `b`.`fileid` WHERE (`a`.`storage` = 2 ) AND (`b`.`fileid` IS NULL) AND (`a`.`path` LIKE 'appdata\\_ocvsye5pcvs4/preview/_/_/_/_/_/_/_/%');
+------+-------------+-------+--------+-----------------------------------------------------------------------------------------------------+------------------------+---------+------------------+------+--------------------------------------+
| id   | select_type | table | type   | possible_keys                                                                                       | key                    | key_len | ref              | rows | Extra                                |
+------+-------------+-------+--------+-----------------------------------------------------------------------------------------------------+------------------------+---------+------------------+------+--------------------------------------+
|    1 | SIMPLE      | a     | range  | fs_storage_path_hash,fs_storage_mimetype,fs_storage_mimepart,fs_storage_size,fs_storage_path_prefix | fs_storage_path_prefix | 267     | NULL             | 282  | Using index condition; Using where   |
|    1 | SIMPLE      | b     | eq_ref | PRIMARY,fs_id_storage_size                                                                          | PRIMARY                | 8       | nextcloud.a.name | 1    | Using where; Using index; Not exists |
+------+-------------+-------+--------+-----------------------------------------------------------------------------------------------------+------------------------+---------+------------------+------+--------------------------------------+
2 rows in set (0.016 sec)

[juliusknorr]

/backport to stable23

[juliusknorr]

/backport to stable22

[juliusknorr]

/backport to stable21

[backportbot-nextcloud]

The backport to stable21 failed. Please do this backport manually.

[backportbot-nextcloud]

The backport to stable22 failed. Please do this backport manually.

[backportbot-nextcloud]

The backport to stable23 failed. Please do this backport manually.