031：Cetus sharding
目录
一、主机环境
- 虚拟机配置
| CPU | 内存 | 硬盘 | OS版本 | MySQL版本 | Cetus版本 |
|---|---|---|---|---|---|
| 2-core | 4G | 500G | CentOS 7.5.1804 | 5.7.18 | v1.0.0-44 |
- 主机信息
| 主机名 | IP地址 | Server_ID | Cetus | 备注 |
|---|---|---|---|---|
| node01 | 192.168.222.171 | 部署 | 监控/MySQL主库的故障转移 | |
| node02 | 192.168.222.172 | 172 | - | |
| node03 | 192.168.222.173 | 173 | - | |
| node04 | 192.168.222.174 | 174 | - |
- 借用官方架构图
二、搭建环境
1、准备环境
1.MySQL
- 5.7.17以上版本（分布式事务功能需要）
- 数据库设计（即分库，根据业务将数据对象分成若干组）
- 创建用户和密码
- 确认Cetus可以远程登录MySQL
2.Cetus
- 根据MySQL后端信息配置users.json、sharding.json和shard.conf（variables.json可选配），具体配置说明详见Cetus 分库(sharding)配置文件说明
3.mysql多实例
直接使用杨建荣快速搭建mgr脚本，配置多实例（不开启mgr）
- Github
- 搭建5个实例端口分别为33061~33065
- 创建测试库
1.创建mysql cetus测试账号 grant all on *.* to gcdb@'%' identified by password 'iforgot'; flush privileges;
2.创建测试库ttt
create database if not exists ttt;
create table ttt.t1(id int(4)primary key not null auto_increment,nums int(20) not null);
insert into ttt.t1(nums) values(1),(2),(3),(4),(5);
update ttt.t1 set nums=100 where id =3;
delete from ttt.t1 where id =4;
select * from ttt.t1;
[root@node06 mgr_scripts]# ps -ef |grep mynode
root 14503 1 0 09:55 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mynode01/mynode01.cnf
mysql 14826 14503 0 09:55 pts/0 00:00:01 /usr/local/mysql/bin/mysqld --defaults-file=/data/mynode01/mynode01.cnf --basedir=/usr/local/mysql --datadir=/data/mynode01 --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/mynode01/node06.test.com.err --pid-file=/data/mynode01/node06.test.com.pid --socket=/data/mynode01/mynode01.sock --port=33061
root 14861 1 0 09:55 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mynode02/mynode02.cnf
mysql 15184 14861 0 09:55 pts/0 00:00:01 /usr/local/mysql/bin/mysqld --defaults-file=/data/mynode02/mynode02.cnf --basedir=/usr/local/mysql --datadir=/data/mynode02 --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/mynode02/node06.test.com.err --pid-file=/data/mynode02/node06.test.com.pid --socket=/data/mynode02/mynode02.sock --port=33062
root 15220 1 0 09:55 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mynode03/mynode03.cnf
mysql 15543 15220 0 09:55 pts/0 00:00:01 /usr/local/mysql/bin/mysqld --defaults-file=/data/mynode03/mynode03.cnf --basedir=/usr/local/mysql --datadir=/data/mynode03 --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/mynode03/node06.test.com.err --pid-file=/data/mynode03/node06.test.com.pid --socket=/data/mynode03/mynode03.sock --port=33063
root 15579 1 0 09:55 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mynode04/mynode04.cnf
mysql 15902 15579 0 09:55 pts/0 00:00:01 /usr/local/mysql/bin/mysqld --defaults-file=/data/mynode04/mynode04.cnf --basedir=/usr/local/mysql --datadir=/data/mynode04 --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/mynode04/node06.test.com.err --pid-file=/data/mynode04/node06.test.com.pid --socket=/data/mynode04/mynode04.sock --port=33064
root 15938 1 0 09:56 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/mynode05/mynode05.cnf
mysql 16261 15938 0 09:56 pts/0 00:00:01 /usr/local/mysql/bin/mysqld --defaults-file=/data/mynode05/mynode05.cnf --basedir=/usr/local/mysql --datadir=/data/mynode05 --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/mynode05/node06.test.com.err --pid-file=/data/mynode05/node06.test.com.pid --socket=/data/mynode05/mynode05.sock --port=33065
三、Cetus安装
1、下载包和安装依赖包
cetus源码下载
git clone https://github.com/Lede-Inc/cetus.git
# 安装Cetus依赖包
yum -y install cmake gcc glib2-devel flex libevent-devel mysql-devel gperftools-libs
# 安装mha依赖包
yum -y install perl-DBD-MySQL perl-Config-Tiny perl-Log-Dispatch perl-Parallel-ForkManager perl-ExtUtils-CBuilder perl-ExtUtils-MakeMaker perl-CPAN perl-ExtUtils-Manifest
2、Cetus安装
1.安装说明
Cetus利用自动化建构系统CMake进行编译安装，其中描述构建过程的构建文件CMakeLists.txt已经在源码中的主目录和子目录中，下载源码并解压后具体安装步骤如下：
- 创建编译目录：在源码主目录下创建独立的目录build，并转到该目录下
mkdir build/
cd build/
- 编译：利用cmake进行编译，指令如下
读写分离版本：
cmake ../ -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/home/user/cetus_install -DSIMPLE_PARSER=ON
分库版本：
cmake ../ -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/home/user/cetus_install -DSIMPLE_PARSER=OFF
其中CMAKE_BUILD_TYPE变量可以选择生成 debug 版和或release 版的程序，CMAKE_INSTALL_PREFIX变量确定软件的实际安装目录的绝对路径，安装目录建议以/home/user/日期.编译版本.分支.commit_id的方式命名；
SIMPLE_PARSER变量确定软件的编译版本，设置为ON则编译读写分离版本，否则编译分库版本。
该过程会检查您的系统是否缺少一些依赖库和依赖软件，可以根据错误代码安装相应依赖。
- 安装：执行make install进行安装
make install
- 配置：Cetus运行前还需要编辑配置文件
cd /home/user/cetus_install/conf/
cp XXX.json.example XXX.json
cp XXX.conf.example XXX.conf
vi XXX.json
vi XXX.conf
配置文件在make insatll后存在示例文件，以.example结尾，目录为/home/user/cetus_install/conf/，包括用户设置文件（users.json）、变量处理配置文件（variables.json）、分库版本的分片规则配置文件（sharding.json）、读写分离版本的启动配置文件（proxy.conf）和分库版本的启动配置文件（shard.conf）。
根据具体编译安装的版本编辑相关配置文件，若使用读写分离功能则需配置users.json和proxy.conf，若使用sharding功能则需配置users.json、sharding.json和shard.conf，其中两个版本的variables.json均可选配。
配置文件的具体说明见Cetus 读写分离版配置文件说明和Cetus 分库(sharding)版配置文件说明。
- 启动：Cetus可以利用bin/cetus启动
读写分离版本：
bin/cetus --defaults-file=conf/proxy.conf [--conf-dir＝/home/user/cetus_install/conf/]
分库版本：
bin/cetus --defaults-file=conf/shard.conf [--conf-dir＝/home/user/cetus_install/conf/]
其中Cetus启动时可以添加命令行选项，--defaults-file选项用来加载启动配置文件（proxy.conf或者shard.conf），且在启动前保证启动配置文件的权限为660；--conf-dir是可选项，用来加载其他配置文件(.json文件)，默认为当前目录下conf文件夹。
Cetus可起动守护进程后台运行，也可在进程意外终止自动启动一个新进程，可通过启动配置选项进行设置。
2.安装实施
#进入源码目录
[root@node01 software]# git clone https://github.com/Lede-Inc/cetus.git
[root@node01 software]# cd cetus/
[root@node01 cetus]# mkdir build/ && cd build
[root@node01 build]# cmake ../ -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/usr/local/cetus -DSIMPLE_PARSER=OFF
[root@node01 build]# make install
[root@node01 build]# ll /usr/local/cetus/
total 0
drwxr-xr-x 2 root root 19 Aug 31 09:29 bin
drwxr-xr-x 2 root root 143 Aug 31 09:29 conf
drwxr-xr-x 4 root root 210 Aug 31 09:29 lib
drwxr-xr-x 2 root root 19 Aug 31 09:29 libexec
drwxr-xr-x 2 root root 23 Aug 31 09:29 logs
四、Cetus配置
1、创建和修改配置文件
- 在manager节点上创建cetus的user和proxy.配置文件（users.json和proxy.conf）
[root@node01 build]# cp /usr/local/cetus/conf/users.json.example /usr/local/cetus/conf/users.json
[root@node01 build]# cp /usr/local/cetus/conf/shard.conf.example /usr/local/cetus/conf/shard.conf
[root@node01 build]# cp /usr/local/cetus/conf/sharding.json.example /usr/local/cetus/conf/sharding.json
[root@node01 build]# vim /usr/local/cetus/conf/users.json
[root@node01 build]# cat /usr/local/cetus/conf/users.json
{
"users": [{
"user": "gcdb",
"client_pwd": "iforgot",
"server_pwd": "iforgot"
}, {
"user": "cetus_app1",
"client_pwd": "cetus_app1",
"server_pwd": "cetus_app1"
}]
}
[root@node01 build]# cat /usr/local/cetus/conf/sharding.json
{
"vdb": [
{
"id": 1,
"type": "int",
"method": "hash",
"num": 10,
"partitions": {"data1": [0,1], "data2": [2,3], "data3": [4,5], "data4": [6,7],"data5": [8,9]}
},
{
"id": 2,
"type": "int",
"method": "range",
"num": 0,
"partitions": {"data1": 99999, "data2": 199999, "data3": 299999,"data4": 399999,"data5": 499999}
}
],
"table": [
{"vdb": 1, "db": "employees_hash", "table": "dept_emp", "pkey": "emp_no"},
{"vdb": 1, "db": "employees_hash", "table": "employees", "pkey": "emp_no"},
{"vdb": 1, "db": "employees_hash", "table": "salaries", "pkey": "emp_no"},
{"vdb": 2, "db": "employees_range", "table": "employees", "pkey": "emp_no"},
{"vdb": 2, "db": "employees_range", "table": "titles", "pkey": "emp_no"}
],
"single_tables": [
{"table": "dept_manager", "db": "employees_hash", "group": "data1"},
{"table": "departments", "db": "employees_hash", "group": "data1"},
{"table": "departments", "db": "employees_range", "group": "data2"}
]
}
[root@node01 build]# vim /usr/local/cetus/conf/shard.conf
[root@node01 build]# cat /usr/local/cetus/conf/shard.conf
[cetus]
# For mode
daemon=true
# Loaded Plugins
plugins=shard,admin
# Proxy Configuration, For eaxmlpe: MySQL master host ip is 192.0.0.1 and salve host ip is 192.0.0.2
#proxy-address=192.168.222.171:8888
proxy-address=0.0.0.0:8888
proxy-backend-addresses=192.168.222.176:33061@data1,192.168.222.176:33062@data2,192.168.222.176:33063@data3,192.168.222.176:33064@data4,192.168.222.176:33065@data5
# Admin Configuration
admin-address=192.168.222.171:9999
admin-username=admin
admin-password=admin
# Backend Configuration, use test db and username created
default-db=ttt
default-username=gcdb
default-pool-size=100
max-pool-size=400
max-resp-=10485760
long-query-time=100
default-charset=utf8
# Log Configuration, put log in /data and marked by proxy port , /data/cetus needs to be created manually and has rw authority for cetus os user
plugin-dir=lib/cetus/plugins
max-open-files=65536
pid-file=cetus.pid
log-xa-file=/var/log/cetus/cetusxa.log
log-file=/var/log/cetus/cetus.log
log-level=debug
# Check salve delay
disable-threads=true
check-slave-delay=true
slave-delay-down=5
slave-delay-recover=1
# For trouble
keepalive=true
verbose-shutdown=true
log-backtrace-on-crash=true
2、启动cetus
- 启动前保证启动配置文件的权限为660
[root@node01 software]# chmod 660 /usr/local/cetus/conf/*
[root@node01 software]# ls /usr/local/cetus/conf/
proxy.conf.example shard.conf shard.conf.example sharding.json sharding.json.bak sharding.json.example users.json users.json.example variables.json.example
- 守护进程模式启动Cetus
- session A
[root@node01 software]# /usr/local/cetus/bin/cetus --defaults-file=/usr/local/cetus/conf/shard.conf
[root@node01 software]# ps -ef |grep cetus
root 21835 20826 0 14:59 pts/3 00:00:00 tailf /var/log/cetus/cetus.log
root 21845 1 0 14:59 ? 00:00:00 /usr/local/cetus/libexec/cetus --defaults-file=/usr/local/cetus/conf/shard.conf
root 21846 21845 4 14:59 ? 00:00:33 /usr/local/cetus/libexec/cetus --defaults-file=/usr/local/cetus/conf/shard.conf
root 22487 26164 0 15:12 pts/2 00:00:00 grep --color=auto cetus
- session B
[root@node01 software]# mkdir -p /mydata
[root@node01 software]# cd /mydata
[root@node01 mydata]# git clone https://github.com/datacharmer/test_db.git
Cloning into 'test_db'...
remote: Counting objects: 102, done.
remote: Total 102 (delta 0), reused 0 (delta 0), pack-reused 102
Receiving objects: 100% (102/102), 68.81 MiB | 274.00 KiB/s, done.
Resolving deltas: 100% (54/54), done.
[root@node01 mydata]# cd test_db/
[root@node01 test_db]# ls
Changelog employees.sql load_dept_emp.dump load_salaries1.dump load_titles.dump sakila test_employees_md5.sql
employees_partitioned_5.1.sql images load_dept_manager.dump load_salaries2.dump objects.sql show_elapsed.sql test_employees_sha.sql
employees_partitioned.sql load_departments.dump load_employees.dump load_salaries3.dump README.md sql_test.sh
[root@node01 test_db]# less employees.sql
DROP DATABASE IF EXISTS employees;
CREATE DATABASE IF NOT EXISTS employees;
USE employees;
SELECT 'CREATING DATABASE STRUCTURE' as 'INFO';
DROP TABLE IF EXISTS dept_emp,
dept_manager,
titles,
salaries,
employees,
departments;
CREATE TABLE employees (
emp_no INT NOT NULL,
birth_date DATE NOT NULL,
first_name VARCHAR(14) NOT NULL,
last_name VARCHAR(16) NOT NULL,
gender ENUM ('M','F') NOT NULL,
hire_date DATE NOT NULL,
PRIMARY KEY (emp_no)
);
CREATE TABLE departments (
dept_no CHAR(4) NOT NULL,
dept_name VARCHAR(40) NOT NULL,
PRIMARY KEY (dept_no),
UNIQUE KEY (dept_name)
);
CREATE TABLE dept_manager (
emp_no INT NOT NULL,
dept_no CHAR(4) NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
FOREIGN KEY (dept_no) REFERENCES departments (dept_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,dept_no)
);
CREATE TABLE dept_emp (
emp_no INT NOT NULL,
dept_no CHAR(4) NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
FOREIGN KEY (dept_no) REFERENCES departments (dept_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,dept_no)
);
CREATE TABLE titles (
emp_no INT NOT NULL,
title VARCHAR(50) NOT NULL,
from_date DATE NOT NULL,
to_date DATE,
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,title, from_date)
)
;
CREATE TABLE salaries (
emp_no INT NOT NULL,
salary INT NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no, from_date)
)
;
-- 把下面这创建视图语句删掉不然导入会报错（ERROR 1149 (42000) at line 98: near "OR": syntax error）
CREATE OR REPLACE VIEW dept_emp_latest_date AS
SELECT emp_no, MAX(from_date) AS from_date, MAX(to_date) AS to_date
FROM dept_emp
GROUP BY emp_no;
# shows only the current department for each employee
CREATE OR REPLACE VIEW current_dept_emp AS
SELECT l.emp_no, dept_no, l.from_date, l.to_date
FROM dept_emp d
INNER JOIN dept_emp_latest_date l
ON d.emp_no=l.emp_no AND d.from_date=l.from_date AND l.to_date = d.to_date;
flush /*!50503 binary */ logs;
# 导入数据按下面顺序导入，不然会有外键报错问题
SELECT 'LOADING departments' as 'INFO';
source load_departments.dump ;
SELECT 'LOADING employees' as 'INFO';
source load_employees.dump ;
SELECT 'LOADING dept_emp' as 'INFO';
source load_dept_emp.dump ;
SELECT 'LOADING dept_manager' as 'INFO';
source load_dept_manager.dump ;
SELECT 'LOADING titles' as 'INFO';
source load_titles.dump ;
SELECT 'LOADING salaries' as 'INFO';
source load_salaries1.dump ;
source load_salaries2.dump ;
source load_salaries3.dump ;
source show_elapsed.sql ;
(END)
- session C
[root@node01 build]# mysql -ugcdb -piforgot -P8888 -h192.168.222.171
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 2
Server version: 5.7.18-log (cetus) MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
(gcdb@192.168.222.171) 14:47:27 [(none)]> status
--------------
mysql Ver 14.14 Distrib 5.7.18, for linux-glibc2.5 (x86_64) using EditLine wrapper
Connection id: 5
Current database:
Current user: gcdb@node01.test.com
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.18-log (cetus) MySQL Community Server (GPL)
Protocol version: 10
Connection: 192.168.222.171 via TCP/IP
Server characterset: utf8
Db characterset: utf8
Client characterset: utf8
Conn. characterset: utf8
TCP port: 8888
--------------
(gcdb@192.168.222.171) 14:47:32 [(none)]>
- session D
[root@node01 ~]# mysql -uadmin -padmin -P9999 -h192.168.222.171
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 1
Server version: 5.7 admin
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
(admin@192.168.222.171) 09:04:03 [(none)]> select * from vdb;
+--------+------------+--------------------------------------------------------------------------------------------------------------------------------+
| VDB id | Method | Partitions |
+--------+------------+--------------------------------------------------------------------------------------------------------------------------------+
| 1 | hash(INT) | [0,1]->data1; [2,3]->data2; [4,5]->data3; [6,7]->data4; [8,9]->data5 |
| 2 | range(INT) | (-2147483648, 99999]->data1; (99999, 199999]->data2; (199999, 299999]->data3; (299999, 399999]->data4; (399999, 499999]->data5 |
+--------+------------+--------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
(admin@192.168.222.171) 09:04:20 [(none)]> select sharded table;
+---------------------------+--------+--------+
| Table | VDB id | Key |
+---------------------------+--------+--------+
| employees_hash.dept_emp | 1 | emp_no |
| employees_hash.employees | 1 | emp_no |
| employees_hash.salaries | 1 | emp_no |
| employees_range.employees | 2 | emp_no |
| employees_range.titles | 2 | emp_no |
+---------------------------+--------+--------+
5 rows in set (0.01 sec)
(admin@192.168.222.171) 09:11:22 [(none)]> select single table ;
+-----------------------------+-------+
| Table | Group |
+-----------------------------+-------+
| employees_hash.dept_manager | data1 |
| employees_hash.departments | data1 |
| employees_range.departments | data2 |
+-----------------------------+-------+
3 rows in set (0.00 sec)
(admin@192.168.222.171) 09:11:28 [(none)]> select * from groups;
+-------+-----------------------+--------+
| group | master | slaves |
+-------+-----------------------+--------+
| data1 | 192.168.222.176:33061 | |
| data2 | 192.168.222.176:33062 | |
| data3 | 192.168.222.176:33063 | |
| data4 | 192.168.222.176:33064 | |
| data5 | 192.168.222.176:33065 | |
+-------+-----------------------+--------+
5 rows in set (0.00 sec)
(admin@192.168.222.171) 09:11:50 [(none)]> select conn_details from backends;select * from backends;
+-------------+----------+------------+------------+-------------+
| backend_ndx | username | idle_conns | used_conns | total_conns |
+-------------+----------+------------+------------+-------------+
| 0 | gcdb | 100 | 0 | 100 |
| 1 | gcdb | 100 | 0 | 100 |
| 2 | gcdb | 100 | 0 | 100 |
| 3 | gcdb | 100 | 0 | 100 |
| 4 | gcdb | 100 | 0 | 100 |
+-------------+----------+------------+------------+-------------+
5 rows in set (0.00 sec)
+-------------+-----------------------+-------+------+-------------+------+------------+------------+-------------+-------+
| backend_ndx | address | state | type | slave delay | uuid | idle_conns | used_conns | total_conns | group |
+-------------+-----------------------+-------+------+-------------+------+------------+------------+-------------+-------+
| 1 | 192.168.222.176:33061 | up | rw | NULL | NULL | 100 | 0 | 100 | data1 |
| 2 | 192.168.222.176:33062 | up | rw | NULL | NULL | 100 | 0 | 100 | data2 |
| 3 | 192.168.222.176:33063 | up | rw | NULL | NULL | 100 | 0 | 100 | data3 |
| 4 | 192.168.222.176:33064 | up | rw | NULL | NULL | 100 | 0 | 100 | data4 |
| 5 | 192.168.222.176:33065 | up | rw | NULL | NULL | 100 | 0 | 100 | data5 |
+-------------+-----------------------+-------+------+-------------+------+------------+------------+-------------+-------+
5 rows in set (0.00 sec)
(admin@192.168.222.171) 09:12:40 [(none)]>
3、导入数据
- 分别创建库和表
-- employees_range创建3张表
create database employees_range;
use employees_range;
CREATE TABLE employees (
emp_no INT NOT NULL,
birth_date DATE NOT NULL,
first_name VARCHAR(14) NOT NULL,
last_name VARCHAR(16) NOT NULL,
gender ENUM ('M','F') NOT NULL,
hire_date DATE NOT NULL,
PRIMARY KEY (emp_no)
);
CREATE TABLE departments (
dept_no CHAR(4) NOT NULL,
dept_name VARCHAR(40) NOT NULL,
PRIMARY KEY (dept_no),
UNIQUE KEY (dept_name)
);
CREATE TABLE titles (
emp_no INT NOT NULL,
title VARCHAR(50) NOT NULL,
from_date DATE NOT NULL,
to_date DATE,
KEY (emp_no),
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,title, from_date)
);
-- employees_hash创建5张表
create database employees_hash;
use employees_hash;
CREATE TABLE employees (
emp_no INT NOT NULL,
birth_date DATE NOT NULL,
first_name VARCHAR(14) NOT NULL,
last_name VARCHAR(16) NOT NULL,
gender ENUM ('M','F') NOT NULL,
hire_date DATE NOT NULL,
PRIMARY KEY (emp_no)
);
CREATE TABLE departments (
dept_no CHAR(4) NOT NULL,
dept_name VARCHAR(40) NOT NULL,
PRIMARY KEY (dept_no),
UNIQUE KEY (dept_name)
);
CREATE TABLE dept_manager (
dept_no CHAR(4) NOT NULL,
emp_no INT NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
KEY (emp_no),
KEY (dept_no),
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
FOREIGN KEY (dept_no) REFERENCES departments (dept_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,dept_no)
);
CREATE TABLE dept_emp (
emp_no INT NOT NULL,
dept_no CHAR(4) NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
KEY (emp_no),
KEY (dept_no),
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
FOREIGN KEY (dept_no) REFERENCES departments (dept_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no,dept_no)
);
CREATE TABLE salaries (
emp_no INT NOT NULL,
salary INT NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
KEY (emp_no),
FOREIGN KEY (emp_no) REFERENCES employees (emp_no) ON DELETE CASCADE,
PRIMARY KEY (emp_no, from_date)
);
- 先导入到employees库，然后备份出来再分批导入到employees_hash和employees_range中
cetus不支持load data infile，不支持lock tables语法，导入employees具体请看README.md
#导入到employees库
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees <employees.sql
#分别备份employees库各个表
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees titles >titles.sql
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees dept_emp >dept_emp.sql
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees salaries >salaries.sql
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees employees >employees.sql
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees dept_manager >dept_manager.sql
mysqldump -ugcdb -piforgot -h192.168.49.176 -P33061 --set-gtid-purged=OFF --complete-insert --no-create-info --skip-add-locks --master-data=2 employees departments >departments.sql
#分批导入到employees_hash和employees_range中
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_range <departments.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_range <employees.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_range <titles.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_hash <departments.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_hash <employees.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_hash <salaries.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_hash <dept_manager.sql
mysql -ugcdb -piforgot -h192.168.222.171 -P8888 employees_hash <dept_emp.sql
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1452 (23000) at line 29: Cannot add or update a child row: a foreign key constraint fails (`employees_hash`.`dept_emp`, CONSTRAINT `dept_emp_ibfk_2` FOREIGN KEY (`dept_no`) REFERENCES `departments` (`dept_no`) ON DELETE CASCADE)
注意导入顺序问题，不然有外键问题，可以先删除外键关联，导入数据后再重建外键
4、验证cetus分库功能
- Cetus主机
(gcdb@192.168.222.171) 09:35:56 [(none)]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 300024 | --employees_hash.employees表总行数300024
+----------+
1 row in set (0.32 sec)
(gcdb@192.168.222.171) 09:36:21 [(none)]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 443308 | --employees_range.titles表总行数443308
+----------+
1 row in set (0.26 sec)
(gcdb@192.168.222.171) 09:40:22 [(none)]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 24 | --employees_hash.dept_manager表总行数24（单点全局表）
+----------+
1 row in set (0.01 sec)
(gcdb@192.168.222.171) 09:41:35 [(none)]>
- mysql主机（多实例）
--mynode01
(root@localhost) 09:38:34 [(none)]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 60004 | --employees_hash.employees表总行数60004(hash分片表)
+----------+
1 row in set (0.03 sec)
(root@localhost) 09:38:41 [(none)]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 133345 | --employees_range.titles表总行数 133345(range分片表)
+----------+
1 row in set (0.05 sec)
(root@localhost) 09:38:43 [(none)]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 24 | --employees_hash.dept_manager表总行数24（单点全局表）
+----------+
1 row in set (0.00 sec)
(root@localhost) 09:40:19 [(none)]>
-------------------------------------------------------
--mynode02
(root@localhost) 09:40:30 [(none)]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 60005 |
+----------+
1 row in set (0.03 sec)
(root@localhost) 09:40:35 [(none)]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 14844 |
+----------+
1 row in set (0.01 sec)
(root@localhost) 09:40:41 [(none)]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)
(root@localhost) 09:40:43 [(none)]>
-------------------------------------------------------
--mynode03
(root@localhost) 09:41:42 [(none)]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 60009 |
+----------+
1 row in set (0.03 sec)
(root@localhost) 09:41:48 [(none)]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 147566 |
+----------+
1 row in set (0.07 sec)
(root@localhost) 09:41:50 [(none)]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.02 sec)
(root@localhost) 09:41:55 [(none)]>
--mynode04
(root@localhost) 09:35:11 [(none)]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 60003 |
+----------+
1 row in set (0.03 sec)
(root@localhost) 09:42:31 [(none)]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)
(root@localhost) 09:42:36 [(none)]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.01 sec)
(root@localhost) 09:42:41 [(none)]>
-------------------------------------------------------
--mynode05
(root@localhost) 09:35:14 [employees_range]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 60003 |
+----------+
1 row in set (0.02 sec)
(root@localhost) 09:43:12 [employees_range]> select count(*) from employees_range.titles;
+----------+
| count(*) |
+----------+
| 147553 |
+----------+
1 row in set (0.06 sec)
(root@localhost) 09:43:13 [employees_range]> select count(*) from employees_hash.dept_manager;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.02 sec)
(root@localhost) 09:43:20 [employees_range]>
五、Cetus测试各种限制
1、JOIN的使用限制
不支持跨库的JOIN，非分片表可以在每个分片中都保存一份，以提高join的使用成功率。
--employees_hash库
(gcdb@192.168.222.171) 11:34:56 [employees_hash]> select * from dept_manager d left join employees a on d.emp_no=a.emp_no ; --dept_manager（全局表）
ERROR 5004 (HY000): (cetus) JOIN single-table WITH sharding-table
(gcdb@192.168.222.171) 11:34:59 [employees_hash]> select * from dept_emp d left join employees a on d.emp_no=a.emp_no limit 10;--（dept_emp分片表）
+--------+---------+------------+------------+--------+------------+------------+-----------+--------+------------+
| emp_no | dept_no | from_date | to_date | emp_no | birth_date | first_name | last_name | gender | hire_date |
+--------+---------+------------+------------+--------+------------+------------+-----------+--------+------------+
| 10001 | d005 | 1986-06-26 | 9999-01-01 | 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 |
| 10010 | d004 | 1996-11-24 | 2000-06-26 | 10010 | 1963-06-01 | Duangkaew | Piveteau | F | 1989-08-24 |
| 10010 | d006 | 2000-06-26 | 9999-01-01 | 10010 | 1963-06-01 | Duangkaew | Piveteau | F | 1989-08-24 |
| 10011 | d009 | 1990-01-22 | 1996-11-09 | 10011 | 1953-11-07 | Mary | Sluis | F | 1990-01-22 |
| 10020 | d004 | 1997-12-30 | 9999-01-01 | 10020 | 1952-12-24 | Mayuko | Warwick | M | 1991-01-26 |
| 10021 | d005 | 1988-02-10 | 2002-07-15 | 10021 | 1960-02-20 | Ramzi | Erde | M | 1988-02-10 |
| 10030 | d004 | 1994-02-17 | 9999-01-01 | 10030 | 1958-07-14 | Elvis | Demeyer | M | 1994-02-17 |
| 10031 | d005 | 1991-09-01 | 9999-01-01 | 10031 | 1959-01-27 | Karsten | Joslin | M | 1991-09-01 |
| 10040 | d005 | 1993-02-14 | 2002-01-22 | 10040 | 1959-09-13 | Weiyi | Meriste | F | 1993-02-14 |
| 10040 | d008 | 2002-01-22 | 9999-01-01 | 10040 | 1959-09-13 | Weiyi | Meriste | F | 1993-02-14 |
+--------+---------+------------+------------+--------+------------+------------+-----------+--------+------------+
10 rows in set (0.01 sec)
(gcdb@192.168.222.171) 11:35:15 [employees_hash]>
2、DISTINCT的限制
针对全局表没有限制；
针对分片表，仅支持DISCTINCT字段同时也是ORDER BY字段，例如：select distinct col1 from tab1 order by col1，
另外为了在使用上更加友好，对于order by未写全的，Cetus会进行补充，例如：selectdistinct col1,col2 from tab1 order by col1，Cetus会改写为 select distinct col1,col2 fromtab1 order by col1,col2，但如果写成select distinct * from tab1，Cetus则会返回错误，为了效率，提倡使用标准写法，以免造成不必要的资源开销。
(gcdb@192.168.222.171) 10:52:27 [employees_range]> select distinct title from titles;
+--------------------+
| title |
+--------------------+
| Assistant Engineer |
| Engineer |
| Manager |
| Senior Engineer |
| Senior Staff |
| Staff |
| Technique Leader |
+--------------------+
7 rows in set (0.52 sec)
(gcdb@192.168.222.171) 10:52:37 [employees_range]> select distinct title from titles order by emp_no; --返回错误
ERROR 5005 (HY000): (proxy)ORDER BY columns must be a subset of DISTINCT columns
(gcdb@192.168.222.171) 10:52:43 [employees_range]> select distinct title,emp_no from titles order by emp_no limit 10;
+-----------------+--------+
| title | emp_no |
+-----------------+--------+
| Senior Engineer | 10001 |
| Staff | 10002 |
| Senior Engineer | 10003 |
| Engineer | 10004 |
| Senior Engineer | 10004 |
| Senior Staff | 10005 |
| Staff | 10005 |
| Senior Engineer | 10006 |
| Senior Staff | 10007 |
| Staff | 10007 |
+-----------------+--------+
10 rows in set (0.01 sec)
(gcdb@192.168.222.171) 10:53:10 [employees_range]>
3、CASE WHEN/IF 的限制
全局表没有限制；针对分片表，不能用于DML语句中，也不能用在GROUP BY后，可以用于SELECT 后，也可以作为过滤条件。
(gcdb@192.168.222.171) 11:15:26 [employees_range]> SELECT
-> emp_no,
-> CASE WHEN gender = 'M' THEN '凸'
-> WHEN gender = 'F' THEN '凹'
-> ELSE NULL END gender,
-> hire_date
-> FROM employees limit 10;
+--------+--------+------------+
| emp_no | gender | hire_date | --Select里面可以引用case when语句
+--------+--------+------------+
| 10001 | 凸 | 1986-06-26 |
| 10002 | 凹 | 1985-11-21 |
| 10003 | 凸 | 1986-08-28 |
| 10004 | 凸 | 1986-12-01 |
| 10005 | 凸 | 1989-09-12 |
| 10006 | 凹 | 1989-06-02 |
| 10007 | 凹 | 1989-02-10 |
| 10008 | 凸 | 1994-09-15 |
| 10009 | 凹 | 1985-02-18 |
| 10010 | 凹 | 1989-08-24 |
+--------+--------+------------+
10 rows in set (0.04 sec)
(gcdb@192.168.222.171) 11:57:11 [employees_range]> select * from employees_range.departments; --employees_hash.departments（单点全局表）
+---------+--------------------+
| dept_no | dept_name |
+---------+--------------------+
| d009 | Customer Service |
| d005 | Development |
| d002 | Finance |
| d003 | Human Resources |
| d001 | Marketing |
| d004 | Production |
| d006 | Quality Management |
| d008 | Research |
| d007 | Sales |
+---------+--------------------+
9 rows in set (0.00 sec)
(gcdb@192.168.222.171) 11:57:24 [employees_range]>
(gcdb@192.168.222.171) 11:57:26 [employees_range]> UPDATE employees_range.departments
-> SET dept_no =
-> CASE WHEN dept_no = 'd001' THEN 'b'
-> WHEN dept_no = 'd002' THEN 'a'
-> ELSE dept_no END
-> WHERE dept_name IN ('Marketing', 'Finance');
Query OK, 2 rows affected (0.06 sec)
Rows matched: 2 Changed: 2 Warnings: 0
(gcdb@192.168.222.171) 11:57:30 [employees_range]> select * from employees_range.departments;
+---------+--------------------+
| dept_no | dept_name |
+---------+--------------------+
| d009 | Customer Service |
| d005 | Development |
| a | Finance |
| d003 | Human Resources |
| b | Marketing |
| d004 | Production |
| d006 | Quality Management |
| d008 | Research |
| d007 | Sales |
+---------+--------------------+
9 rows in set (0.01 sec)
(gcdb@192.168.222.171) 10:12:41 [(none)]> UPDATE employees_range.employees
-> SET gender =
-> CASE WHEN gender = 'M' THEN 'men'
-> WHEN gender = 'F' THEN 'wen'
-> ELSE gender END
-> WHERE emp_no < 10003;
Query OK, 2 rows affected, 2 warnings (0.03 sec)
Rows matched: 2 Changed: 2 Warnings: 2
(gcdb@192.168.222.171) 10:13:24 [(none)]>
(gcdb@192.168.222.171) 10:13:31 [(none)]> select * from employees_range.employees limit 10;
+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date |
+--------+------------+------------+-----------+--------+------------+
| 10001 | 1953-09-02 | Georgi | Facello | | 1986-06-26 | --update case when语句没生效
| 10002 | 1964-06-02 | Bezalel | Simmel | | 1985-11-21 |
| 10003 | 1959-12-03 | Parto | Bamford | M | 1986-08-28 |
| 10004 | 1954-05-01 | Chirstian | Koblick | M | 1986-12-01 |
| 10005 | 1955-01-21 | Kyoichi | Maliniak | M | 1989-09-12 |
| 10006 | 1953-04-20 | Anneke | Preusig | F | 1989-06-02 |
| 10007 | 1957-05-23 | Tzvetan | Zielinski | F | 1989-02-10 |
| 10008 | 1958-02-19 | Saniya | Kalloufi | M | 1994-09-15 |
| 10009 | 1952-04-19 | Sumant | Peac | F | 1985-02-18 |
| 10010 | 1963-06-01 | Duangkaew | Piveteau | F | 1989-08-24 |
+--------+------------+------------+-----------+--------+------------+
10 rows in set (0.00 sec)
(gcdb@192.168.222.171) 10:13:35 [(none)]>
4、中文列名的限制
对表列的中文列名或别名的使用有限制，使用中文列名或中文别名时必须加引号｀｀
(gcdb@192.168.222.171) 11:43:11 [employees_hash]> select emp_no,birth_date from employees order by emp_no limit 10;
+--------+------------+
| emp_no | birth_date |
+--------+------------+
| 10001 | 1953-09-02 |
| 10002 | 1964-06-02 |
| 10003 | 1959-12-03 |
| 10004 | 1954-05-01 |
| 10005 | 1955-01-21 |
| 10008 | 1958-02-19 |
| 10006 | 1953-04-20 |
| 10007 | 1957-05-23 |
| 10009 | 1952-04-19 |
| 10010 | 1963-06-01 |
+--------+------------+
10 rows in set (0.00 sec)
(gcdb@192.168.222.171) 11:43:37 [employees_hash]> select emp_no,birth_date as 生日 from employees order by emp_no limit 10;
ERROR 1149 (42000): near "as 堺 syntax errornear "as 堺 syntax error
(gcdb@192.168.222.171) 11:43:49 [employees_hash]> select emp_no,birth_date as '生日' from employees order by emp_no limit 10;
+--------+------------+
| emp_no | 生日 |
+--------+------------+
| 10001 | 1953-09-02 |
| 10002 | 1964-06-02 |
| 10003 | 1959-12-03 |
| 10004 | 1954-05-01 |
| 10005 | 1955-01-21 |
| 10008 | 1958-02-19 |
| 10006 | 1953-04-20 |
| 10007 | 1957-05-23 |
| 10009 | 1952-04-19 |
| 10010 | 1963-06-01 |
+--------+------------+
10 rows in set (0.00 sec)
(gcdb@192.168.222.171) 11:44:01 [employees_hash]>
5、查询业务的限制
在做SQL查询时，应注意以下约束：只支持同一个 VDB 内的关联查询；
针对 sharding 表，在查询条件中可以使用 sharding key 的要求加上该过滤条件， 另外，使用 sharding key 时，不建议使用带有函数转换、算术表达式等逻辑处理, 会严重影响效率。
--内连接join，titles表和employees
(gcdb@192.168.222.171) 10:31:39 [employees_range]> select * from employees e,titles t where e.emp_no = t.emp_no order by e.emp_no limit 5;
+--------+------------+------------+-----------+--------+------------+--------+-----------------+------------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date | emp_no | title | from_date | to_date |
+--------+------------+------------+-----------+--------+------------+--------+-----------------+------------+------------+
| 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 | 10001 | Senior Engineer | 1986-06-26 | 9999-01-01 |
| 10002 | 1964-06-02 | Bezalel | Simmel | F | 1985-11-21 | 10002 | Staff | 1996-08-03 | 9999-01-01 |
| 10003 | 1959-12-03 | Parto | Bamford | M | 1986-08-28 | 10003 | Senior Engineer | 1995-12-03 | 9999-01-01 |
| 10004 | 1954-05-01 | Chirstian | Koblick | M | 1986-12-01 | 10004 | Engineer | 1986-12-01 | 1995-12-01 |
| 10004 | 1954-05-01 | Chirstian | Koblick | M | 1986-12-01 | 10004 | Senior Engineer | 1995-12-01 | 9999-01-01 |
+--------+------------+------------+-----------+--------+------------+--------+-----------------+------------+------------+
5 rows in set (0.00 sec)
--内连接join，titles表和employees_hash.employees（跨库JOIN）
(gcdb@192.168.222.171) 10:32:00 [employees_range]> select * from employees_hash.employees e,titles t where e.emp_no = t.emp_no order by e.emp_no limit 5;
+--------+------------+------------+-----------+--------+------------+--------+------------------+------------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date | emp_no | title | from_date | to_date |
+--------+------------+------------+-----------+--------+------------+--------+------------------+------------+------------+
| 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 | 10001 | Senior Engineer | 1986-06-26 | 9999-01-01 |
| 10010 | 1963-06-01 | Duangkaew | Piveteau | F | 1989-08-24 | 10010 | Engineer | 1996-11-24 | 9999-01-01 |
| 10011 | 1953-11-07 | Mary | Sluis | F | 1990-01-22 | 10011 | Staff | 1990-01-22 | 1996-11-09 |
| 10020 | 1952-12-24 | Mayuko | Warwick | M | 1991-01-26 | 10020 | Engineer | 1997-12-30 | 9999-01-01 |
| 10021 | 1960-02-20 | Ramzi | Erde | M | 1988-02-10 | 10021 | Technique Leader | 1988-02-10 | 2002-07-15 |
+--------+------------+------------+-----------+--------+------------+--------+------------------+------------+------------+
5 rows in set (0.12 sec) --结果错误
(gcdb@192.168.222.171) 10:32:20 [employees_range]> select count(*) from employees_hash.employees;
+----------+
| count(*) |
+----------+
| 300024 |
+----------+
1 row in set (0.08 sec)
(gcdb@192.168.222.171) 10:32:50 [employees_range]> select count(*) from employees_range.employees;
+----------+
| count(*) |
+----------+
| 300024 |
+----------+
1 row in set (0.23 sec)
(gcdb@192.168.222.171) 10:32:55 [employees_range]> explain select * from employees_hash.employees e,titles t where e.emp_no = t.emp_no order by e.emp_no limit 5;
+----+-------------+-------+------------+-------+----------------+---------+---------+-------------------------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+----------------+---------+---------+-------------------------+------+----------+-------+
| 1 | SIMPLE | e | NULL | index | PRIMARY | PRIMARY | 4 | NULL | 3 | 100.00 | NULL |
| 1 | SIMPLE | t | NULL | ref | PRIMARY,emp_no | PRIMARY | 4 | employees_hash.e.emp_no | 1 | 100.00 | NULL |
+----+-------------+-------+------------+-------+----------------+---------+---------+-------------------------+------+----------+-------+
2 rows in set, 1 warning (0.02 sec)
(gcdb@192.168.222.171) 10:33:43 [employees_range]> explain select * from employees e,titles t where e.emp_no = t.emp_no order by e.emp_no limit 5;
+----+-------------+-------+------------+-------+----------------+---------+---------+--------------------------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------+----------------+---------+---------+--------------------------+------+----------+-------+
| 1 | SIMPLE | e | NULL | index | PRIMARY | PRIMARY | 4 | NULL | 3 | 100.00 | NULL |
| 1 | SIMPLE | t | NULL | ref | PRIMARY,emp_no | PRIMARY | 4 | employees_range.e.emp_no | 1 | 100.00 | NULL |
+----+-------------+-------+------------+-------+----------------+---------+---------+--------------------------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)