Это query
:
EXPLAIN (analyze, BUFFERS, SETTINGS)
SELECT
operation.id
FROM
operation
RIGHT JOIN(
SELECT uid, did FROM (
SELECT uid, did FROM operation where id = 993754
) t
) parts ON (operation.uid = parts.uid AND operation.did = parts.did)
и EXPLAIN
информация:
Nested Loop Left Join (cost=0.85..29695.77 rows=100 width=8) (actual time=13.709..13.711 rows=1 loops=1)
Buffers: shared hit=4905
-> Unique (cost=0.42..8.45 rows=1 width=16) (actual time=0.011..0.013 rows=1 loops=1)
Buffers: shared hit=5
-> Index Only Scan using oi on operation operation_1 (cost=0.42..8.44 rows=1 width=16) (actual time=0.011..0.011 rows=1 loops=1)
Index Cond: (id = 993754)
Heap Fetches: 1
Buffers: shared hit=5
-> Index Only Scan using oi on operation (cost=0.42..29686.32 rows=100 width=24) (actual time=13.695..13.696 rows=1 loops=1)
Index Cond: ((uid = operation_1.uid) AND (did = operation_1.did))
Heap Fetches: 1
Buffers: shared hit=4900
Settings: max_parallel_workers_per_gather = '4', min_parallel_index_scan_size = '0', min_parallel_table_scan_size = '0', parallel_setup_cost = '0', parallel_tuple_cost = '0', work_mem = '256MB'
Planning Time: 0.084 ms
Execution Time: 13.728 ms
Почему Nested Loop
стоит все больше и больше времени, чем сумма дочерних элементов? Что я могу для этого сделать? Execution Time
должно быть меньше 1 мс, верно?
Обновить:
Nested Loop Left Join (cost=5.88..400.63 rows=101 width=8) (actual time=0.012..0.012 rows=1 loops=1)
Buffers: shared hit=8
-> Index Scan using oi on operation operation_1 (cost=0.42..8.44 rows=1 width=16) (actual time=0.005..0.005 rows=1 loops=1)
Index Cond: (id = 993754)
Buffers: shared hit=4
-> Bitmap Heap Scan on operation (cost=5.45..391.19 rows=100 width=24) (actual time=0.004..0.005 rows=1 loops=1)
Recheck Cond: ((uid = operation_1.uid) AND (did = operation_1.did))
Heap Blocks: exact=1
Buffers: shared hit=4
-> Bitmap Index Scan on ou (cost=0.00..5.42 rows=100 width=0) (actual time=0.003..0.003 rows=1 loops=1)
Index Cond: ((uid = operation_1.uid) AND (did = operation_1.did))
Buffers: shared hit=3
Settings: max_parallel_workers_per_gather = '4', min_parallel_index_scan_size = '0', min_parallel_table_scan_size = '0', parallel_setup_cost = '0', parallel_tuple_cost = '0', work_mem = '256MB'
Planning Time: 0.127 ms
Execution Time: 0.028 ms
Спасибо всем вам, когда я разделил индекс на btree(id)
и btree(uid, did)
, все прошло идеально, но почему их нельзя использовать вместе? Какие-то подробности или правила?
Кстати, sql используется для расчета в реальном времени, здесь не показан код некоторых оконных функций.