Long planning time

db-standby-1-prod [classroom_prod] # EXPLAIN ANALYZE SELECT "math_adaptive_assignment_sessions"."student_id", "math_adaptive_assignments"."domain_id", count (*) FROM "math_adaptive_assignments" INNER JOIN "math_adaptive_assignment_sessions" ON "math_adaptive_assignments"."id" = "math_adaptive_assignment_sessions"."assignment_id" INNER JOIN "knowledge_snapshots" ON "math_adaptive_assignment_sessions"."knowledge_snapshot_id" = "knowledge_snapshots"."id" INNER JOIN "answers" ON "knowledge_snapshots"."id" = "answers"."knowledge_snapshot_id" WHERE ("math_adaptive_assignment_sessions"."student_id" IN (7538860)) AND (("math_adaptive_assignment_sessions"."completed_at" >= '2017-09-08 08:00:00Z') AND (("math_adaptive_assignment_sessions"."completed_at" <= '2017-09-08 18:02:08.431692Z') AND ("answers"."correctness" >= 100.0))) GROUP BY "math_adaptive_assignment_sessions"."student_id", "math_adaptive_assignments"."domain_id";
                                                                                                     QUERY PLAN                                                                                                      
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 GroupAggregate  (cost=273.74..273.86 rows=6 width=21) (actual time=0.025..0.025 rows=0 loops=1)
   Group Key: math_adaptive_assignment_sessions.student_id, math_adaptive_assignments.domain_id
   ->  Sort  (cost=273.74..273.75 rows=6 width=13) (actual time=0.023..0.023 rows=0 loops=1)
         Sort Key: math_adaptive_assignments.domain_id
         Sort Method: quicksort  Memory: 25kB
         ->  Nested Loop  (cost=2.00..273.66 rows=6 width=13) (actual time=0.019..0.019 rows=0 loops=1)
               Join Filter: (math_adaptive_assignment_sessions.knowledge_snapshot_id = answers.knowledge_snapshot_id)
               ->  Nested Loop  (cost=1.56..269.67 rows=1 width=25) (actual time=0.018..0.018 rows=0 loops=1)
                     ->  Nested Loop  (cost=1.14..261.21 rows=1 width=17) (actual time=0.018..0.018 rows=0 loops=1)
                           ->  Index Scan using math_adaptive_assignment_sessions_student_id_idx on math_adaptive_assignment_sessions  (cost=0.57..252.61 rows=1 width=12) (actual time=0.017..0.017 rows=0 loops=1)
                                 Index Cond: (student_id = 7538860)
                                 Filter: ((completed_at >= '2017-09-08 08:00:00+00'::timestamp with time zone) AND (completed_at <= '2017-09-08 18:02:08.431692+00'::timestamp with time zone))
                                 Rows Removed by Filter: 3
                           ->  Index Scan using math_adaptive_assignments_pkey on math_adaptive_assignments  (cost=0.57..8.59 rows=1 width=13) (never executed)
                                 Index Cond: (id = math_adaptive_assignment_sessions.assignment_id)
                     ->  Index Only Scan using knowledge_snapshots_parent_pkey on knowledge_snapshots  (cost=0.43..8.45 rows=1 width=8) (never executed)
                           Index Cond: (id = math_adaptive_assignment_sessions.knowledge_snapshot_id)
                           Heap Fetches: 0
               ->  Index Scan using answers_parent_knowledge_snapshot_id_idx on answers  (cost=0.44..3.25 rows=59 width=4) (never executed)
                     Index Cond: (knowledge_snapshot_id = knowledge_snapshots.id)
                     Filter: (correctness >= '100'::double precision)
 Planning time: 366.453 ms
 Execution time: 0.079 ms
(23 rows)

Time: 457.075 ms