Postgresql解释分析实际时间不相加

问题描述 投票：0回答：1

我有一个查询，当在我的 postgresql 数据库上运行时，随着查询数量的增加，执行时间会不断增加。在高负载期间，我使用解释分析从 Dbeaver 手动运行相同的查询，计划时间花费了约 9 秒，执行时间花费了 1 秒。但如果我将结果查询中的所有实际时间相加，我不会得到接近 9 秒的结果。

我也没有多个循环。以下是解释分析结果：

Nested Loop Left Join  (cost=26304.72..35480113.45 rows=624544385412 width=1843) (actual time=0.277..0.284 rows=1 loops=1)
  ->  Nested Loop  (cost=26304.15..907648.85 rows=320874 width=1495) (actual time=0.215..0.218 rows=1 loops=1)
        ->  Index Scan using idx_info_part_13_test_id on test_part_13 "Model"  (cost=0.69..8.71 rows=1 width=976) (actual time=0.140..0.142 rows=1 loops=1)
              Index Cond: ((test_id)::text = 'sjbvas6dsad4sad7asda7sd567as5f7dsdf75sdfsdf6sdf5sfas78d6fdsdsada'::text)
        ->  Bitmap Heap Scan on outputs_p_33 "Model"  (cost=26303.46..904431.40 rows=320874 width=519) (actual time=0.060..0.061 rows=1 loops=1)
              Recheck Cond: ((test_id)::text = 'sjbvas6dsad4sad7asda7sd567as5f7dsdf75sdfsdf6sdf5sfas78d6fdsdsada'::text)
              Heap Blocks: exact=1
              ->  Bitmap Index Scan on pk_test_p_33  (cost=0.00..26223.24 rows=320874 width=0) (actual time=0.055..0.055 rows=1 loops=1)
                    Index Cond: ((test_id)::text = 'sjbvas6dsad4sad7asda7sd567as5f7dsdf75sdfsdf6sdf5sfas78d6fdsdsada'::text)
  ->  Append  (cost=0.56..107.54 rows=20 width=348) (actual time=0.046..0.049 rows=1 loops=1)
        ->  Index Scan using addresses_part_0_address_id_idx on addresses_part_0 "ModelType"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_1_address_id_idx on addresses_part_1 "ModelType_1"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_2_address_id_idx on addresses_part_2 "ModelType_2"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_3_address_id_idx on addresses_part_3 "ModelType_3"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_4_address_id_idx on addresses_part_4 "ModelType_4"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_5_address_id_idx on addresses_part_5 "ModelType_5"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_6_address_id_idx on addresses_part_6 "ModelType_6"  (cost=0.56..5.37 rows=1 width=348) (actual time=0.042..0.042 rows=1 loops=1)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_7_address_id_idx on addresses_part_7 "ModelType_7"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_8_address_id_idx on addresses_part_8 "ModelType_8"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_9_address_id_idx on addresses_part_9 "ModelType_9"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_10_address_id_idx on addresses_part_10 "ModelType_10"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_11_address_id_idx on addresses_part_11 "ModelType_11"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_12_address_id_idx on addresses_part_12 "ModelType_12"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_13_address_id_idx on addresses_part_13 "ModelType_13"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_14_address_id_idx on addresses_part_14 "ModelType_14"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_15_address_id_idx on addresses_part_15 "ModelType_15"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_16_address_id_idx on addresses_part_16 "ModelType_16"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_17_address_id_idx on addresses_part_17 "ModelType_17"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_18_address_id_idx on addresses_part_18 "ModelType_18"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
        ->  Index Scan using addresses_part_19_address_id_idx on addresses_part_19 "ModelType_19"  (cost=0.56..5.37 rows=1 width=348) (never executed)
              Index Cond: ((address_id)::text = ("Model".address_id)::text)
Planning Time: 9127.562 ms
Execution Time: 1.090 ms

如果我从结果中添加“实际时间”，我不应该得到相同的秒数吗？为什么差别这么大？

postgresql explain
1个回答
0
投票
  1. 使用 this 检查您的执行计划。
  2. 这些不会相加，因为它们没有必要。来自文档中的 使用 
    EXPLAIN
    ： 

    Planning time
    所示的
    EXPLAIN ANALYZE
    是从解析的查询生成查询计划并对其进行优化所花费的时间。它不包括解析或重写。

    Execution time
    显示的
    EXPLAIN ANALYZE
    包括执行器启动和关闭时间，以及运行任何已触发的触发器的时间

  3. 文档解释了这些测量值的具体含义：

    显示的实际时间和行值是每次执行的平均值

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