简介
TiDB实战篇-基于索引的SQL优化。
Online DDL
允许直接在线执行ddl操作，不会锁表，但是执行多个ddl的时候会要排队。
原理
控制创建索引的速度
查看影响
标红的是加了多少行索引。
添加索引的线上的影响（读写频繁）
只读场景
不涉及读写
索引扫描的方式
直接从索性计算
索引选择的规则
实操
优化创建索引的是时间
mysql -h192.168.66.10 -P4000 -uroot -ptidb
#创建数据库
create database test2;
create table t1(a int,b int);
#导入数据
for i in `seq 10000`; do mysql -uroot -P4000 -ptidb -h192.168.66.10 -e "insert into test2.t1 values($i,floor(rand()*10000000))";done;
for i in `seq 33`; do mysql -uroot -P4000 -ptidb -h192.168.66.10 -e "insert into test2.t1 select * from test2.t1 limit 100000";done;
#调节创建索引速度的参数
set global tidb_ddl_reorg_worker_cnt=1;
set global tidb_ddl_reorg_batch_size=32;
#创建索引
mysql -h192.168.66.10 -P4000 -uroot -ptidb
use test2;
create index index_t1_a on t1(a);
#查看索引创建的速度
admin show ddl jobs where table_name = 't1';
mysql>admin show ddl jobs where table_name = 't1';
+--------+---------+------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------------------+---------+
| JOB_ID | DB_NAME | TABLE_NAME | JOB_TYPE | SCHEMA_STATE | SCHEMA_ID | TABLE_ID | ROW_COUNT | CREATE_TIME | START_TIME | END_TIME | STATE |
+--------+---------+------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------------------+---------+
| 86 | test2 | t1 | add index | write reorganization | 82 | 84 | 479488 | 2023-04-30 14:44:51 | 2023-04-30 14:44:51 | NULL | running |
| 85 | test2 | t1 | create table | public | 82 | 84 | 0 | 2023-04-30 14:39:45 | 2023-04-30 14:39:45 | 2023-04-30 14:39:45 | synced |
| 80 | test2 | t1 | create table | public | 77 | 79 | 0 | 2023-04-30 12:59:23 | 2023-04-30 12:59:23 | 2023-04-30 12:59:23 | synced |
+--------+---------+------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------------------+---------+
3 rows in set (0.01 sec)
Query OK, 0 rows affected (3 min 20.92 sec)
#调节创建索引速度的参数
set global tidb_ddl_reorg_worker_cnt=32;
set global tidb_ddl_reorg_batch_size=512;
#删除掉之前的索引
alter table t1 drop index index_t1_a;
#重新创建索引
create index index_t1_a on t1(a);
用时Query OK, 0 rows affected (2 min 44.09 sec)
Point_Get
#point get触发
mysql -h192.168.66.10 -P4000 -uroot -ptidb
create database test3;
use test3;
create table t1(a int,b int);
#导入实验数据
for i in `seq 10000`; do mysql -uroot -P4000 -ptidb -h192.168.66.10 -e "insert into test3.t1 values($i,floor(rand()*10000000))";done;
for i in `seq 33`; do mysql -uroot -P4000 -ptidb -h192.168.66.10 -e "insert into test3.t1 select * from test2.t1 limit 100000";done;
#查看导入数据和执行计划
select count(*) from t1;
explain select * from t1 where a=888;
mysql> explain select * from t1 where a=888;
+-------------------------+---------+-----------+---------------+--------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------+---------+-----------+---------------+--------------------------------+
| TableReader_7 | 3.91 | root | | data:Selection_6 |
| └─Selection_6 | 3.91 | cop[tikv] | | eq(test3.t1.a, 888) |
| └─TableFullScan_5 | 3906.00 | cop[tikv] | table:t1 | keep order:false, stats:pseudo |
+-------------------------+---------+-----------+---------------+--------------------------------+
3 rows in set (0.00 sec)
#添加索引(非唯一索引)
create index idx on t1(a);
explain select * from t1 where a=888;
mysql> explain select * from t1 where a=888;
+-------------------------------+---------+-----------+------------------------+-----------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------------+---------+-----------+------------------------+-----------------------------------+
| IndexLookUp_10 | 1.00 | root | | |
| ├─IndexRangeScan_8(Build) | 1.00 | cop[tikv] | table:t1, index:idx(a) | range:[888,888], keep order:false |
| └─TableRowIDScan_9(Probe) | 1.00 | cop[tikv] | table:t1 | keep order:false |
+-------------------------------+---------+-----------+------------------------+-----------------------------------+
3 rows in set (0.00 sec)
#添加唯一索引
alter table t1 drop index idx;
create unique index idx on t1(a);
explain select * from t1 where a=888;
mysql> explain select * from t1 where a=888;
+-------------+---------+------+------------------------+---------------+
| id | estRows | task | access object | operator info |
+-------------+---------+------+------------------------+---------------+
| Point_Get_1 | 1.00 | root | table:t1, index:idx(a) | |
+-------------+---------+------+------------------------+---------------+
1 row in set (0.00 sec)
#测试非等值查询
explain select * from t1 where a>888;
mysql> explain select * from t1 where a>888;
+-------------------------+----------+-----------+---------------+---------------------+
| id | estRows | task | access object | operator info |
+-------------------------+----------+-----------+---------------+---------------------+
| TableReader_7 | 9112.00 | root | | data:Selection_6 |
| └─Selection_6 | 9112.00 | cop[tikv] | | gt(test3.t1.a, 888) |
| └─TableFullScan_5 | 10000.00 | cop[tikv] | table:t1 | keep order:false |
+-------------------------+----------+-----------+---------------+---------------------+
3 rows in set (0.01 sec)
#测试空值是否会触发
insert into t1 values(null,10000);
explain select * from t1 where a is null;
mysql> explain select * from t1 where a is null;
+-------------------------------+---------+-----------+------------------------+-------------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------------+---------+-----------+------------------------+-------------------------------------+
| IndexLookUp_10 | 1.00 | root | | |
| ├─IndexRangeScan_8(Build) | 1.00 | cop[tikv] | table:t1, index:idx(a) | range:[NULL,NULL], keep order:false |
| └─TableRowIDScan_9(Probe) | 1.00 | cop[tikv] | table:t1 | keep order:false |
+-------------------------------+---------+-----------+------------------------+-------------------------------------+
3 rows in set (0.00 sec)
