2022-07-30 mysql8执行慢SQL-Q17分析

摘要:

以mysql8.0.28执行Q17慢SQL,作为分析对比

环境信息:

1. 内存: 8GB
2. cpu: 8核心，3.2GHz
3. mysql: 8.0.28

执行分析:

DDL:

mysql> show create table lineitem\G
*************************** 1. row ***************************
       Table: lineitem
Create Table: CREATE TABLE `lineitem` (
  `l_orderkey` int NOT NULL,
  `l_partkey` int NOT NULL,
  `l_suppkey` int NOT NULL,
  `l_linenumber` int NOT NULL,
  `l_quantity` decimal(15,2) NOT NULL,
  `l_extendedprice` decimal(15,2) NOT NULL,
  `l_discount` decimal(15,2) NOT NULL,
  `l_tax` decimal(15,2) NOT NULL,
  `l_returnflag` char(1) NOT NULL,
  `l_linestatus` char(1) NOT NULL,
  `l_shipdate` date NOT NULL,
  `l_commitdate` date NOT NULL,
  `l_receiptdate` date NOT NULL,
  `l_shipinstruct` char(25) NOT NULL,
  `l_shipmode` char(10) NOT NULL,
  `l_comment` varchar(44) NOT NULL,
  PRIMARY KEY (`l_orderkey`,`l_linenumber`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> show create table part\G
*************************** 1. row ***************************
       Table: part
Create Table: CREATE TABLE `part` (
  `p_partkey` int NOT NULL,
  `p_name` varchar(55) NOT NULL,
  `p_mfgr` char(25) NOT NULL,
  `p_brand` char(10) NOT NULL,
  `p_type` varchar(25) NOT NULL,
  `p_size` int NOT NULL,
  `p_container` char(10) NOT NULL,
  `p_retailprice` decimal(15,2) NOT NULL,
  `p_comment` varchar(23) NOT NULL,
  PRIMARY KEY (`p_partkey`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.02 sec)

SQL:

select
    sum(l_extendedprice) / 7.0 as avg_yearly
from
    lineitem,
    part
where
    p_partkey = l_partkey
    and p_brand = 'Brand#23'
    and p_container = 'MED BOX'
    and l_quantity < (
        select
            0.2 * avg(l_quantity)
        from
            lineitem
        where
            l_partkey = p_partkey
    );

explain分析:

mysql> explain select
     from
            lineitem
        where
            l_partkey = p_partkey
    )\G    ->     sum(l_extendedprice) / 7.0 as avg_yearly
    -> from
    ->     lineitem,
    ->     part
    -> where
    ->     p_partkey = l_partkey
    ->     and p_brand = 'Brand#23'
    ->     and p_container = 'MED BOX'
    ->     and l_quantity < (
    ->         select
    ->             0.2 * avg(l_quantity)
    ->         from
    ->             lineitem
    ->         where
    ->             l_partkey = p_partkey
    ->     )\G
*************************** 1. row ***************************
           id: 1
  select_type: PRIMARY
        table: lineitem
   partitions: NULL
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 31751480
     filtered: 100.00
        Extra: NULL
*************************** 2. row ***************************
           id: 1
  select_type: PRIMARY
        table: part
   partitions: NULL
         type: eq_ref
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 4
          ref: tpch.lineitem.l_partkey
         rows: 1
     filtered: 5.00
        Extra: Using where
*************************** 3. row ***************************
           id: 2
  select_type: DEPENDENT SUBQUERY
        table: lineitem
   partitions: NULL
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 31751480
     filtered: 10.00
        Extra: Using where
3 rows in set, 2 warnings (0.01 sec)

id

select_type

table

partitions

type

possible_keys

key

key_len

ref

rows

filtered

Extra

1

PRIMARY

lineitem

ALL

31751480

100

1

PRIMARY

part

eq_ref

PRIMARY

PRIMARY

4

tpch.lineitem.l_partkey

1

5

Using where

2

DEPENDENT SUBQUERY

lineitem

ALL

31751480

10

Using where

耗时分析:

性能分析:

iotop:

top:

[[email protected] ~]# ps -ef | grep mysqld
mysql      19895       1 39 20:21 ?        00:18:16 /usr/libexec/mysqld --basedir=/usr
root       20055    1793  0 21:07 pts/1    00:00:00 grep --color=auto mysqld
[[email protected] ~]# 
[[email protected] ~]# top -Hp 19895

热力图: