Create index for 'fid_content_id' in flag_content

Hiya,

I have a few views which reference the flag module and I was finding that whenever the query (this is on a site with 100k+ nodes of which only a few hundred have been flagged) was running, the query would take approximately 1.5 seconds. As a reference the query is something like:
SELECT node.nid AS nid, node.title AS node_title, node_data_field_photo_lossy_image.field_photo_lossy_image_fid AS node_data_field_photo_lossy_image_field_photo_lossy_image_fid, node_data_field_photo_lossy_image.field_photo_lossy_image_list AS node_data_field_photo_lossy_image_field_photo_lossy_image_list, node_data_field_photo_lossy_image.field_photo_lossy_image_data AS node_data_field_photo_lossy_image_field_photo_lossy_image_data, node.type AS node_type, node.vid AS node_vid, flag_content_node.timestamp AS flag_content_node_timestamp, flag_content_node_1.timestamp AS flag_content_node_1_timestamp, DATE_FORMAT((FROM_UNIXTIME(flag_content_node.timestamp) + INTERVAL -25200 SECOND), '%Y') AS flag_content_node_timestamp_year, DATE_FORMAT((FROM_UNIXTIME(flag_content_node_1.timestamp) + INTERVAL -25200 SECOND), '%Y') AS flag_content_node_1_timestamp_year, node.nid AS node_nid FROM node node LEFT JOIN content_type_calarts_photo node_data_field_photo_lossy_image ON node.vid = node_data_field_photo_lossy_image.vid INNER JOIN files files_node_data_field_photo_lossy_image ON node_data_field_photo_lossy_image.field_photo_lossy_image_fid = files_node_data_field_photo_lossy_image.fid LEFT JOIN flag_content flag_content_node ON node.nid = flag_content_node.content_id AND flag_content_node.fid = 4 LEFT JOIN flag_content flag_content_node_1 ON node.nid = flag_content_node_1.content_id AND flag_content_node_1.fid = 3 LEFT JOIN content_field_photo_gallery node_data_field_photo_gallery ON node.vid = node_data_field_photo_gallery.vid WHERE (node.status <> 0 OR (node.uid = 1 AND 1 <> 0) OR 1 = 1) AND (node_data_field_photo_gallery.field_photo_gallery_nid = 205385) ORDER BY flag_content_node_timestamp_year DESC, flag_content_node_1_timestamp_year DESC, node_title ASC, node_nid ASC LIMIT 0, 12
(Yes, I know the query looks quite nasty). Anyways, I was noticing that when I ran an explain on the query, it would be using the unique index 'fid_content_type_content_id_uid' but in that scenario the content_type is missing so the only index that is really being used in this scenario is fid which brings in a lot more rows.

To resolve this issue, I did a query CREATE INDEX fid_content_id ON flag_content(fid, content_id); and once I ran the explain, this index was being used and when I ran the query, the query time went down from 1.5 seconds to 0.05.

Even though I did this on D6 (and I'm currently using 1.3), I saw that the index on 1.3, 2.x for D6 and D7 were the same. So the patch I propose would be:
For D6:

  $return = array();
  db_add_index($return, 'flag_content', 'fid_content_id', array('fid', 'content_id'));

For D7:

  db_add_index('flag_content', 'fid_content_id', array('fid', 'content_id'));