Problem/Motivation
admin/content/files is very slow for us on a site that has lots of files.
mysql> explain SELECT file_managed.filename AS file_managed_filename, file_managed.created AS file_managed_created, file_managed.changed AS file_managed_changed, file_managed.fid AS fid, SUM(file_usage_file_managed.count) AS file_usage_file_managed_count, MIN(file_managed.fid) AS fid_1
-> FROM
-> file_managed file_managed
-> LEFT JOIN file_usage file_usage_file_managed ON file_managed.fid = file_usage_file_managed.fid
-> GROUP BY file_managed_filename, file_managed_created, file_managed_changed, file_managed.fid
-> ORDER BY file_managed_created DESC
-> LIMIT 51 OFFSET 0;
+----+-------------+-------------------------+------+------------------------------+---------+---------+-----------------------------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------------------+------+------------------------------+---------+---------+-----------------------------+--------+---------------------------------+
| 1 | SIMPLE | file_managed | ALL | NULL | NULL | NULL | NULL | 184075 | Using temporary; Using filesort |
| 1 | SIMPLE | file_usage_file_managed | ref | PRIMARY,fid_count,fid_module | PRIMARY | 4 | file_managed.fid | 1 | NULL |
+----+-------------+-------------------------+------+------------------------------+---------+---------+-----------------------------+--------+---------------------------------+
mysql> SELECT /* sql_no_cache */ file_managed.filename AS file_managed_filename, file_managed.type AS file_managed_type, file_managed.created AS file_managed_created, file_managed.changed AS file_managed_changed, file_managed.fid AS fid, SUM(file_usage_file_managed.count) AS file_usage_file_managed_count, MIN(file_managed.fid) AS fid_1 FROM file_managed file_managed LEFT JOIN file_usage file_usage_file_managed ON file_managed.fid = file_usage_file_managed.fid GROUP BY file_managed_filename, file_managed_type, file_managed_created, file_managed_changed, file_managed.fid ORDER BY file_managed_created DESC LIMIT 51 OFFSET 0;
...
51 rows in set (2.77 sec)
I thought it could be the order by on created which doesn't have an index, but changing to changed, which has doesn't change anything.
Proposed resolution
I guess it's join to the file usage table and then the optimization gets confused. IIRC, we had a similar problem with authors on admin/content that now loads the users separately. I think we should do the same with file usage. Stop trying to load the info but have a custom field plugin that just uses the file usage API to load that information for the files that are being displayed.
There is no API to get that information for multiple files, so we either have to live with doing 50 fast queries or querying the table directly (or extending the API). Since we already join the table directly, doing a direct query won't be a regression in terms of DB abstraction..
Without the SUM and LEFT join, the query is 0.06s instead of 2.7 even on created, with changed it's obviously 0.00. so not a big issue anymore. Explain:
mysql> explain SELECT file_managed.filename AS file_managed_filename, file_managed.created AS file_managed_created, file_managed.changed AS file_managed_changed, file_managed.fid AS fid FROM file_managed file_managed ORDER BY file_managed_created DESC LIMIT 51 OFFSET 0;
+----+-------------+--------------+------+---------------+------+---------+------+--------+----------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+--------------+------+---------------+------+---------+------+--------+----------------+
| 1 | SIMPLE | file_managed | ALL | NULL | NULL | NULL | NULL | 184075 | Using filesort |
+----+-------------+--------------+------+---------------+------+---------+------+--------+----------------+
mysql> explain SELECT file_managed.filename AS file_managed_filename, file_managed.created AS file_managed_created, file_managed.changed AS file_managed_changed, file_managed.fid AS fid FROM file_managed file_managed ORDER BY file_managed_changed DESC LIMIT 51 OFFSET 0;
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+-------+
| 1 | SIMPLE | file_managed | index | NULL | file_field__changed | 4 | NULL | 51 | NULL |
+----+-------------+--------------+-------+---------------+---------------------+---------+------+------+-------+
1 row in set (0.00 sec)
Remaining tasks
User interface changes
API changes
Data model changes
