Обсуждение: Query Plan difference between 9.3 and 9.5 for the worse. Help !!!
9.3 Explain
Index Scan using target_account_type_idx on targets t (cost=3.92..146295.18 rows=701 width=42)
Index Cond: ((account_id = ANY ('removed for privacy'::bigint[])) AND (type = 'KeyTransaction'::text))
Filter: (SubPlan 1)
SubPlan 1
-> Limit (cost=91.69..91.69 rows=1 width=334)
-> Sort (cost=91.69..92.14 rows=183 width=334)
Sort Key: c.id
-> Nested Loop (cost=0.85..90.77 rows=183 width=334)
-> Index Scan using condition_targets_target_id_idx on condition_targets ct (cost=0.43..14.68 rows=9 width=56)
Index Cond: (target_id = t.id)
-> Index Scan using index_conditions_family_id_archived_at on conditions c (cost=0.42..8.45 rows=1 width=278)
Index Cond: (family_id = ct.condition_family_id)
Filter: ((id >= ct.created_condition_id) AND ((id < ct.removed_condition_id) OR (ct.removed_condition_id IS NULL)))
(13 rows)
9.5 Explain
Hash Join (cost=655687.56..674049.55 rows=28 width=42)
Hash Cond: (t.id = ct.target_id)
-> Index Scan using target_account_type_idx on targets t (cost=0.56..18356.43 rows=1556 width=50)
Index Cond: ((account_id = ANY ('{removed for privacy }'::bigint[])) AND
(type = 'KeyTransaction'::text))
-> Hash (cost=652267.43..652267.43 rows=273566 width=8)
-> HashAggregate (cost=649531.77..652267.43 rows=273566 width=8)
Group Key: ct.target_id
-> Nested Loop (cost=2545.42..518241.47 rows=52516119 width=8)
-> Bitmap Heap Scan on conditions c (cost=2544.99..100917.01 rows=144108 width=16)
Recheck Cond: (archived_at IS NULL)
-> Bitmap Index Scan on index_conditions_family_id_archived_at (cost=0.00..2508.96 rows=144108 width=0)
-> Index Scan using condition_targets_idx on condition_targets ct (cost=0.43..2.53 rows=37 width=32)
Index Cond: ((condition_family_id = c.family_id) AND (c.id >= created_condition_id))
Filter: ((c.id < removed_condition_id) OR (removed_condition_id IS NULL))
(14 rows)
Jorge Torralba
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Jorge Torralba <jorge.torralba@gmail.com> writes: > We have been struggling with a query on our system that under 9.3 was > taking 15ms or so to run and after upgrading to 9.5 it is taking over > 2500ms. > You can see the explains are very different but I cannot figure out why > when using the same data on both system. Hard to comment on this when you haven't shown us the query nor the table schemas. But I'm going to guess based on the lack of a Limit node in the second plan that your query involves WHERE EXISTS(SELECT ... LIMIT 1). The LIMIT 1 would have defeated optimization till recently, but now the planner knows that it's a no-op in this context and throws it away, and then is able to convert the sub-select to a semijoin. Usually that results in a better plan; there's far from enough info here to guess why it's worse for you. regards, tom lane