Possible speedup: Add an index for aggregator_item

Before adding an index on fid:

desc SELECT i.title, i.timestamp, i.link FROM aggregator_item i WHERE i.fid =5 ORDER BY i.timestamp DESC LIMIT 0, 20;

+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------+
| 1 | SIMPLE | i | ALL | NULL | NULL | NULL | NULL | 2069 | Using where; Using filesort |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------+

After adding an index on fid:
alter table aggregator_item add index(fid);

desc SELECT i.title, i.timestamp, i.link FROM aggregator_item i WHERE i.fid =5 ORDER BY i.timestamp DESC LIMIT 0, 20;
+----+-------------+-------+------+---------------+------+---------+-------+------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+-------+------+-----------------------------+
| 1 | SIMPLE | i | ref | fid | fid | 4 | const | 93 | Using where; Using filesort |
+----+-------------+-------+------+---------------+------+---------+-------+------+-----------------------------+