Addons: improve DB query for projects_feature table

[humitos]

This small improvements reduces the db query from ~20ms to ~1ms.

Original query:

Limit  (cost=6753.56..6753.77 rows=21 width=24) (actual time=26.139..26.144 rows=13 loops=1)
   ->  HashAggregate  (cost=6753.56..6753.87 rows=31 width=24) (actual time=26.138..26.142 rows=13 loops=1)
         Group Key: projects_feature.feature_id
         ->  Hash Right Join  (cost=1.70..6556.54 rows=78808 width=24) (actual time=0.055..26.118 rows=54 loops=1)
               Hash Cond: (projects_feature_projects.feature_id = projects_feature.id)
               Filter: ((projects_feature_projects.project_id = 256207) OR ((projects_feature.add_date > '2018-12-05 10:47:06.794648+00'::timestamp with time zone) AND projects_feature.default_true) OR ((projects_feature.add_date <= '2018-12-05 10:47:06.794648+00'::timestamp with time zone) AND projects_feature.future_default_true))
               Rows Removed by Filter: 73672
               ->  Seq Scan on projects_feature_projects  (cost=0.00..5669.03 rows=274603 width=8) (actual time=0.006..7.502 rows=73715 loops=1)
               ->  Hash  (cost=1.31..1.31 rows=31 width=38) (actual time=0.041..0.042 rows=31 loops=1)
                     Buckets: 1024  Batches: 1  Memory Usage: 11kB
                     ->  Seq Scan on projects_feature  (cost=0.00..1.31 rows=31 width=38) (actual time=0.006..0.010 rows=31 loops=1)
 Planning Time: 0.396 ms
 Execution Time: 26.173 ms
(13 rows)

New query:

 Limit  (cost=0.56..6405.06 rows=7 width=24) (actual time=0.015..0.039 rows=2 loops=1)
   ->  Unique  (cost=0.56..6405.06 rows=7 width=24) (actual time=0.015..0.038 rows=2 loops=1)
         ->  Nested Loop Left Join  (cost=0.56..6360.57 rows=17795 width=24) (actual time=0.014..0.035 rows=7 loops=1)
               Filter: ((projects_feature_projects.project_id = 256207) OR ((projects_feature.add_date > '2018-12-05 10:47:06.794648+00'::timestamp with time zone) AND projects_feature.default_true) OR ((projects_feature.add_date <= '2018-12-05 10:47:06.794648+00'::timestamp with time zone) AND projects_feature.future_default_true))
               Rows Removed by Filter: 9
               ->  Index Scan using projects_feature_feature_id_key on projects_feature  (cost=0.14..12.68 rows=7 width=38) (actual time=0.003..0.011 rows=8 loops=1)
                     Filter: ((feature_id)::text ~~ 'addons\_%'::text)
                     Rows Removed by Filter: 23
               ->  Index Only Scan using projects_feature_projects_feature_id_a684910e_uniq on projects_feature_projects  (cost=0.42..606.49 rows=17163 width=8) (actual time=0.002..0.002 rows=2 loops=8)
                     Index Cond: (feature_id = projects_feature.id)
                     Heap Fetches: 11
 Planning Time: 0.275 ms
 Execution Time: 0.058 ms
(13 rows)