TPCH的Q11语句执行计划生成时间过长

人如其名 · 2023 年1 月 23 日 14:14

【 TiDB 使用环境】测试
【 TiDB 版本】6.5.0
在测试TPCH的Q11语句时候发现语句执行计划生成时间过长，语句为：

select /*+   TPCH_Q11  */
        ps_partkey,
        sum(ps_supplycost * ps_availqty) as value
from
        partsupp,
        supplier,
        nation
where
        ps_suppkey = s_suppkey
        and s_nationkey = n_nationkey
        and n_name = 'GERMANY'
group by
        ps_partkey having
                sum(ps_supplycost * ps_availqty) > (
                        select
                                sum(ps_supplycost * ps_availqty) * 0.0000100000
                        from
                                partsupp,
                                supplier,
                                nation
                        where
                                ps_suppkey = s_suppkey
                                and s_nationkey = n_nationkey
                                and n_name = 'GERMANY'
                )
order by
        value desc;

具体执行计划如下：

mysql> explain select 
    ->         ps_partkey,
    ->         sum(ps_supplycost * ps_availqty) as value
    -> from
    ->         partsupp,
    ->         supplier,
    ->         nation
    -> where
    ->         ps_suppkey = s_suppkey
    ->         and s_nationkey = n_nationkey
    ->         and n_name = 'GERMANY'
    -> group by
    ->         ps_partkey having
    ->                 sum(ps_supplycost * ps_availqty) > (
    ->                         select
    ->                                 sum(ps_supplycost * ps_availqty) * 0.0000100000
    ->                         from
    ->                                 partsupp,
    ->                                 supplier,
    ->                                 nation
    ->                         where
    ->                                 ps_suppkey = s_suppkey
    ->                                 and s_nationkey = n_nationkey
    ->                                 and n_name = 'GERMANY'
    ->                 )
    -> order by
    ->         value desc;
+--------------------------------------------+------------+-----------+----------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id                                         | estRows    | task      | access object  | operator info                                                                                                                                              |
+--------------------------------------------+------------+-----------+----------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Projection_63                              | 257648.92  | root      |                | tpch1.partsupp.ps_partkey, Column#33                                                                                                                       |
| └─Sort_64                                  | 257648.92  | root      |                | Column#33:desc                                                                                                                                             |
|   └─Selection_66                           | 257648.92  | root      |                | gt(Column#33, 8102913.765246800000)                                                                                                                        |
|     └─HashAgg_67                           | 322061.15  | root      |                | group by:Column#58, funcs:sum(Column#56)->Column#33, funcs:firstrow(Column#57)->tpch1.partsupp.ps_partkey                                                  |
|       └─Projection_94                      | 322061.15  | root      |                | mul(tpch1.partsupp.ps_supplycost, cast(tpch1.partsupp.ps_availqty, decimal(20,0) BINARY))->Column#56, tpch1.partsupp.ps_partkey, tpch1.partsupp.ps_partkey |
|         └─HashJoin_71                      | 322061.15  | root      |                | inner join, equal:[eq(tpch1.supplier.s_suppkey, tpch1.partsupp.ps_suppkey)]                                                                                |
|           ├─HashJoin_84(Build)             | 4000.00    | root      |                | inner join, equal:[eq(tpch1.nation.n_nationkey, tpch1.supplier.s_nationkey)]                                                                               |
|           │ ├─TableReader_89(Build)        | 1.00       | root      |                | data:Selection_88                                                                                                                                          |
|           │ │ └─Selection_88               | 1.00       | cop[tikv] |                | eq(tpch1.nation.n_name, "GERMANY")                                                                                                                         |
|           │ │   └─TableFullScan_87         | 25.00      | cop[tikv] | table:nation   | keep order:false                                                                                                                                           |
|           │ └─TableReader_86(Probe)        | 100000.00  | root      |                | data:TableFullScan_85                                                                                                                                      |
|           │   └─TableFullScan_85           | 100000.00  | cop[tikv] | table:supplier | keep order:false                                                                                                                                           |
|           └─TableReader_91(Probe)          | 8000000.00 | root      |                | data:TableFullScan_90                                                                                                                                      |
|             └─TableFullScan_90             | 8000000.00 | cop[tikv] | table:partsupp | keep order:false                                                                                                                                           |
+--------------------------------------------+------------+-----------+----------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
14 rows in set (1.14 sec)

语句总体执行时间不长（包含生成执行计划时间一共才2.x秒）：

mysql> explain analyze select 
    ->         ps_partkey,
    ->         sum(ps_supplycost * ps_availqty) as value
    -> from
    ->         partsupp,
    ->         supplier,
    ->         nation
    -> where
    ->         ps_suppkey = s_suppkey
    ->         and s_nationkey = n_nationkey
    ->         and n_name = 'GERMANY'
    -> group by
    ->         ps_partkey having
    ->                 sum(ps_supplycost * ps_availqty) > (
    ->                         select
    ->                                 sum(ps_supplycost * ps_availqty) * 0.0000100000
    ->                         from
    ->                                 partsupp,
    ->                                 supplier,
    ->                                 nation
    ->                         where
    ->                                 ps_suppkey = s_suppkey
    ->                                 and s_nationkey = n_nationkey
    ->                                 and n_name = 'GERMANY'
    ->                 )
    -> order by
    ->         value desc;
+--------------------------------------------+------------+---------+-----------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+---------+
| id                                         | estRows    | actRows | task      | access object  | execution info                                                                                                                                                                                                                                                                                     | operator info                                                                                                                                              | memory    | disk    |
+--------------------------------------------+------------+---------+-----------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+---------+
| Projection_63                              | 257648.92  | 8685    | root      |                | time:1.27s, loops:10, Concurrency:3                                                                                                                                                                                                                                                                | tpch1.partsupp.ps_partkey, Column#33                                                                                                                       | 221.0 KB  | N/A     |
| └─Sort_64                                  | 257648.92  | 8685    | root      |                | time:1.27s, loops:10                                                                                                                                                                                                                                                                               | Column#33:desc                                                                                                                                             | 485.7 KB  | 0 Bytes |
|   └─Selection_66                           | 257648.92  | 8685    | root      |                | time:1.26s, loops:10                                                                                                                                                                                                                                                                               | gt(Column#33, 8102913.765246800000)                                                                                                                        | 48.5 KB   | N/A     |
|     └─HashAgg_67                           | 322061.15  | 304774  | root      |                | time:1.25s, loops:300                                                                                                                                                                                                                                                                              | group by:Column#58, funcs:sum(Column#56)->Column#33, funcs:firstrow(Column#57)->tpch1.partsupp.ps_partkey                                                  | 66.5 MB   | 0 Bytes |
|       └─Projection_94                      | 322061.15  | 323920  | root      |                | time:877.6ms, loops:319, Concurrency:3                                                                                                                                                                                                                                                             | mul(tpch1.partsupp.ps_supplycost, cast(tpch1.partsupp.ps_availqty, decimal(20,0) BINARY))->Column#56, tpch1.partsupp.ps_partkey, tpch1.partsupp.ps_partkey | 355.5 KB  | N/A     |
|         └─HashJoin_71                      | 322061.15  | 323920  | root      |                | time:1.17s, loops:319, build_hash_table:{total:7.12ms, fetch:6.22ms, build:901.5µs}, probe:{concurrency:3, total:3.62s, max:1.21s, probe:610.4ms, fetch:3.01s}                                                                                                                                     | inner join, equal:[eq(tpch1.supplier.s_suppkey, tpch1.partsupp.ps_suppkey)]                                                                                | 308.5 KB  | 0 Bytes |
|           ├─HashJoin_84(Build)             | 4000.00    | 4049    | root      |                | time:6.57ms, loops:7, build_hash_table:{total:596.2µs, fetch:590.9µs, build:5.28µs}, probe:{concurrency:3, total:19.6ms, max:6.53ms, probe:5.04ms, fetch:14.5ms}                                                                                                                                   | inner join, equal:[eq(tpch1.nation.n_nationkey, tpch1.supplier.s_nationkey)]                                                                               | 25.7 KB   | 0 Bytes |
|           │ ├─TableReader_89(Build)        | 1.00       | 1       | root      |                | time:577.5µs, loops:2, cop_task: {num: 1, max: 1.01ms, proc_keys: 25, rpc_num: 1, rpc_time: 977.4µs, copr_cache_hit_ratio: 0.00, distsql_concurrency: 5}                                                                                                                                           | data:Selection_88                                                                                                                                          | 317 Bytes | N/A     |
|           │ │ └─Selection_88               | 1.00       | 1       | cop[tikv] |                | tikv_task:{time:1ms, loops:1}, scan_detail: {total_process_keys: 25, total_process_keys_size: 3109, total_keys: 26, get_snapshot_time: 30.1µs, rocksdb: {key_skipped_count: 25, block: {cache_hit_count: 8}}}                                                                                      | eq(tpch1.nation.n_name, "GERMANY")                                                                                                                         | N/A       | N/A     |
|           │ │   └─TableFullScan_87         | 25.00      | 25      | cop[tikv] | table:nation   | tikv_task:{time:0s, loops:1}                                                                                                                                                                                                                                                                       | keep order:false                                                                                                                                           | N/A       | N/A     |
|           │ └─TableReader_86(Probe)        | 100000.00  | 100000  | root      |                | time:4.23ms, loops:100, cop_task: {num: 10, max: 1.02ms, min: 209.3µs, avg: 506.7µs, p95: 1.02ms, max_proc_keys: 480, p95_proc_keys: 480, rpc_num: 10, rpc_time: 4.94ms, copr_cache_hit_ratio: 0.90, distsql_concurrency: 5}                                                                       | data:TableFullScan_85                                                                                                                                      | 964.4 KB  | N/A     |
|           │   └─TableFullScan_85           | 100000.00  | 100000  | cop[tikv] | table:supplier | tikv_task:{proc max:637ms, min:1ms, avg: 160.4ms, p80:491ms, p95:637ms, iters:137, tasks:10}, scan_detail: {total_process_keys: 480, total_process_keys_size: 87745, total_keys: 481, get_snapshot_time: 102.5µs, rocksdb: {key_skipped_count: 480, block: {cache_hit_count: 10}}}                 | keep order:false                                                                                                                                           | N/A       | N/A     |
|           └─TableReader_91(Probe)          | 8000000.00 | 8000000 | root      |                | time:947.7ms, loops:7840, cop_task: {num: 292, max: 47.8ms, min: 171.1µs, avg: 15.6ms, p95: 37.7ms, max_proc_keys: 50144, p95_proc_keys: 50144, tot_proc: 3.41s, tot_wait: 336ms, rpc_num: 292, rpc_time: 4.55s, copr_cache_hit_ratio: 0.12, distsql_concurrency: 5}                               | data:TableFullScan_90                                                                                                                                      | 11.3 MB   | N/A     |
|             └─TableFullScan_90             | 8000000.00 | 8000000 | cop[tikv] | table:partsupp | tikv_task:{proc max:43ms, min:0s, avg: 11.5ms, p80:22ms, p95:27ms, iters:8969, tasks:292}, scan_detail: {total_process_keys: 7206272, total_process_keys_size: 1336557763, total_keys: 7206528, get_snapshot_time: 5.21ms, rocksdb: {key_skipped_count: 7206272, block: {cache_hit_count: 23171}}} | keep order:false                                                                                                                                           | N/A       | N/A     |
+--------------------------------------------+------------+---------+-----------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------+---------+
14 rows in set (2.35 sec)

trace plan信息如下：
trace_plan.json (61.3 KB)

请问为何生成执行计划需要1秒多时间呢？

Lucien-卢西恩 · 2023 年1 月 28 日 06:50

@人如其名可以提供一下对应的 Json 分析截图么？这个我在本地没有解析成功，另外最好提供一下 table schema 信息，我可以在自己测试环境尝试复现一下。如果是生成执行计划慢，同时是 Optimizer 问题，我可以复现的。

人如其名 · 2023 年1 月 28 日 07:05

你好，可以直接生成tpch来复现（指定sf=1，很快就完成）：
tiup bench tpch -D tpch -H 192.168.31.201 -P 5432 -U root -p root --sf=1 prepare -T 5 --dropdata

然后执行上面的explain信息。

也可以用如下建表结构：

mysql> show create table partsupp;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                                                                                                                                                                                                    |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| partsupp | CREATE TABLE `partsupp` (
  `PS_PARTKEY` bigint(20) NOT NULL,
  `PS_SUPPKEY` bigint(20) NOT NULL,
  `PS_AVAILQTY` bigint(20) NOT NULL,
  `PS_SUPPLYCOST` decimal(15,2) NOT NULL,
  `PS_COMMENT` varchar(199) NOT NULL,
  PRIMARY KEY (`PS_PARTKEY`,`PS_SUPPKEY`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create table supplier;
+----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                                                                                                                                                                                                                                             |
+----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| supplier | CREATE TABLE `supplier` (
  `S_SUPPKEY` bigint(20) NOT NULL,
  `S_NAME` char(25) NOT NULL,
  `S_ADDRESS` varchar(40) NOT NULL,
  `S_NATIONKEY` bigint(20) NOT NULL,
  `S_PHONE` char(15) NOT NULL,
  `S_ACCTBAL` decimal(15,2) NOT NULL,
  `S_COMMENT` varchar(101) NOT NULL,
  PRIMARY KEY (`S_SUPPKEY`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> show create table nation;
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                                                                                                                                                                                          |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| nation | CREATE TABLE `nation` (
  `N_NATIONKEY` bigint(20) NOT NULL,
  `N_NAME` char(25) NOT NULL,
  `N_REGIONKEY` bigint(20) NOT NULL,
  `N_COMMENT` varchar(152) DEFAULT NULL,
  PRIMARY KEY (`N_NATIONKEY`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

人如其名 · 2023 年1 月 28 日 07:10

我自己测试了下，空表复现不了，应该和统计信息有关。
还是需要完整复现，tiup bench tpch -D tpch -H 192.168.31.201 -P 5432 -U root -p root --sf=10 prepare -T 5 --dropdata --analyze

人如其名 · 2023 年1 月 28 日 08:08

感觉和having的子查询有关，有如下两个测试：
1、去掉子查询中的where条件形成笛卡尔积查询则执行计划一直运行跑不出结果：

explain
select 
        ps_partkey,
        sum(ps_supplycost * ps_availqty) as value
from
        partsupp,
        supplier,
        nation
where
        ps_suppkey = s_suppkey
        and s_nationkey = n_nationkey
        and n_name = 'GERMANY'
group by
        ps_partkey having
                sum(ps_supplycost * ps_availqty) > (
                        select
                                sum(ps_supplycost * ps_availqty) * 0.0000100000
                        from
                                partsupp,
                                supplier,
                                nation
--                        where
--                                ps_suppkey = s_suppkey
--                                and s_nationkey = n_nationkey
--                                and n_name = 'GERMANY'
                )
order by
        value desc;

2、去掉子查询中关联条件只保留partsupp，可以秒出：

explain
select 
        ps_partkey,
        sum(ps_supplycost * ps_availqty) as value
from
        partsupp,
        supplier,
        nation
where
        ps_suppkey = s_suppkey
        and s_nationkey = n_nationkey
        and n_name = 'GERMANY'
group by
        ps_partkey having
                sum(ps_supplycost * ps_availqty) > (
                        select
                                sum(ps_supplycost * ps_availqty) * 0.0000100000
                        from
                                partsupp
                )
order by
        value desc;

tiancaiamao · 2023 年4 月 12 日 04:51

人如其名:

                        select
                                sum(ps_supplycost * ps_availqty) * 0.0000100000
                        from
                                partsupp,
                                supplier,
                                nation
                        where
                                ps_suppkey = s_suppkey
                                and s_nationkey = n_nationkey
                                and n_name = 'GERMANY'

这个原因是，这是一个非关联子查询，tidb 在 编译期提前把这个子查询执行 并得到结果了，
再拿得到的结果，去继续构造 plan，然后再执行…

你注意观察一下 plan 可以发现，

这个东西里面 8102913.765246800000 就是子查询提前计算出来的结果
sum(ps_supplycost * ps_availqty) > (select 子查询 )
就被转成了 gt(Column#33, 8102913.765246800000) 这样的条件

所以你看到的生成执行计划时间过长，是因为在生成执行计划的过程中执行了子查询的 sql，并且耗时算在生成计划里面了。
这个问题被提了好多次，总是没有解掉，目前有一点积重难返的感觉…

人如其名 · 2023 年4 月 12 日 11:57

原来如此，多谢大牛！

system · 2023 年6 月 11 日 11:58

此话题已在最后回复的 60 天后被自动关闭。不再允许新回复。