Question

我有2个表 scheduling_flownode 和 xact_message ，它们之间的关系微弱。我正在尝试执行以下查询

set search_path='ad_96d5be';
explain analyze 
SELECT f.id, f.target_object_id 
FROM "scheduling_flownode" f, 
     "xact_message" m 
where f.target_object_id = m.id 
and f.root_node=True 
AND f.state=1 
and m.state=4 
and m.templatelanguage_id IN (17, 18, 19, 20, 21, 22, 23, 24);

执行后，我得到以下查询计划

  Gather  (cost=252701.26..1711972.04 rows=374109 width=8) (actual time=17737.908..164181.063 rows=441130 loops=1)
   Workers Planned: 2
   Workers Launched: 2
   Buffers: shared hit=35705 read=1346425, temp read=18190 written=18148
   ->  Hash Join  (cost=251701.26..1673561.14 rows=155879 width=8) (actual time=18805.587..163991.468 rows=147043 loops=3)
         Hash Cond: (f.target_object_id = m.id)
         Buffers: shared hit=35705 read=1346425, temp read=18190 written=18148
         ->  Parallel Bitmap Heap Scan on scheduling_flownode f  (cost=124367.21..1523127.76 rows=2061083 width=8) (actual time=963.910..155466.840 rows=1642157 loops=3)
               Recheck Cond: (state = 1)
               Rows Removed by Index Recheck: 44
               Filter: root_node
               Rows Removed by Filter: 12406874
               Heap Blocks: exact=10570 lossy=427078
               Buffers: shared read=1328631
               ->  Bitmap Index Scan on "root-node-and-state"  (cost=0.00..123130.57 rows=4946600 width=0) (actual time=955.044..955.045 rows=4926472 loops=1)
                     Index Cond: ((root_node = true) AND (state = 1))
                     Buffers: shared read=13464
         ->  Hash  (cost=120677.64..120677.64 rows=405712 width=4) (actual time=7124.131..7124.131 rows=441128 loops=3)
               Buckets: 131072  Batches: 8  Memory Usage: 2966kB
               Buffers: shared hit=35591 read=17793, temp written=3384
               ->  Bitmap Heap Scan on xact_message m  (cost=7893.56..120677.64 rows=405712 width=4) (actual time=61.307..6925.456 rows=441128 loops=3)
                     Recheck Cond: (state = 4)
                     Filter: (templatelanguage_id = ANY ('{17,18,19,20,21,22,23,24}'::integer[]))
                     Rows Removed by Filter: 4
                     Heap Blocks: exact=16585
                     Buffers: shared hit=35591 read=17793
                     ->  Bitmap Index Scan on "state-index"  (cost=0.00..7792.13 rows=421826 width=0) (actual time=58.781..58.781 rows=441132 loops=3)
                           Index Cond: (state = 4)
                           Buffers: shared hit=2420 read=1209
 Planning time: 1.382 ms
 Execution time: 164289.481 ms
(31 rows)

scheduling_flownode 这里有超过40万条条目，而 xact_message 有约50000行。在postgres 10上工作时，我是否错误地认为postgres应该可以轻松处理这么多的负载？如果可以，我在这里的查询有问题吗？

Answer 1

您没有显示所拥有的索引，但是我强烈建议您的索引将覆盖您要过滤的所有列。

在Postgres 11中，可以使用COVERING indexes完成操作，因此，例如在表scheduling_flownode上，您将拥有一个类似以下的索引：

CREATE INDEX ix_scheduling_flownode_target_object_id 
  ON scheduling_flownode(target_object_id) 
    INCLUDE (state, root_node);

在Postgres 10中，只需在索引中包括以下列：

CREATE INDEX ix_scheduling_flownode_target_object_id 
  ON scheduling_flownode(target_object_id, state, root_node);

使用xact_message和templatelanguage_id对表state执行相同操作。

在Postgres中加入表演

1 个答案: