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I'm having some trouble getting this query down for large users.   Basically, we deal with competition entries.  For this customer (a.k.a. site) we've got ~1,000,000 entries from ~100,000 contestants.

SELECT  contestants.*, sum(entries.worth) as db_entries, count(entries.id) as db_actions FROM "contestants" INNER JOIN "entries" ON "entries"."contestant_id" = "contestants"."id" WHERE "entries"."campaign_id" IN (SELECT id FROM "campaigns"  WHERE "campaigns"."site_id" = $1) AND (entries.status != 'Invalid') GROUP BY contestants.id  ORDER BY db_actions desc LIMIT 20 OFFSET 0

Here's the explain:

                                                               QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=3783168.28..3783168.33 rows=20 width=103)
   ->  Sort  (cost=3783168.28..3792902.85 rows=3893825 width=103)
         Sort Key: (count(entries.id))
         ->  GroupAggregate  (cost=3004896.86..3679555.00 rows=3893825 width=103)
               ->  Merge Join  (cost=3004896.86..3611413.06 rows=3893825 width=103)
                     Merge Cond: (contestants.id = entries.contestant_id)
                     ->  Index Scan using contestants_pkey on contestants  (cost=0.43..534782.85 rows=7490021 width=95)
                     ->  Sort  (cost=3004710.57..3014464.64 rows=3901628 width=12)
                           Sort Key: entries.contestant_id
                           ->  Nested Loop  (cost=19.88..2577567.27 rows=3901628 width=12)
                                 ->  Bitmap Heap Scan on campaigns  (cost=19.32..1332.62 rows=374 width=4)
                                       Recheck Cond: (site_id = 152)
                                       ->  Bitmap Index Scan on index_campaigns_on_site_id  (cost=0.00..19.22 rows=374 width=0)
                                             Index Cond: (site_id = 152)
                                 ->  Index Scan using index_entries_on_campaign_id on entries  (cost=0.57..6784.01 rows=10432 width=16)
                                       Index Cond: (campaign_id = campaigns.id)
                                       Filter: ((status)::text <> 'Invalid'::text)

Any thoughts on tweaks I could apply to speed this up?