如果想新创建集群，需要保证有新的管理节点、计算节点和存储节点。在此给你提个建议，尽量不要把多个项目的数据库放在同一个集群下，很麻烦的，我们公司的项目就因为甲方资源紧张，没办法，三个项目用了一个cluster的集群，结果只要其中一个项目使用数据库资源过大，就会把三个项目一起影响。
所以如果资源足够的话，尽量拆成多个集群。
在开始演示之前，我们先介绍下两个概念。
概念一，数据的可选择性基数，也就是常说的cardinality值。
查询优化器在生成各种执行计划之前，得先从统计信息中取得相关数据，这样才能估算每步 *** 作所涉及到的记录数，而这个相关数据就是cardinality。简单来说，就是每个值在每个字段中的唯一值分布状态。
比如表t1有100行记录，其中一列为f1。f1中唯一值的个数可以是100个，也可以是1个，当然也可以是1到100之间的任何一个数字。这里唯一值越的多少，就是这个列的可选择基数。
那看到这里我们就明白了，为什么要在基数高的字段上建立索引，而基数低的的字段建立索引反而没有全表扫描来的快。当然这个只是一方面，至于更深入的探讨就不在我这篇探讨的范围了。
概念二，关于HINT的使用。
这里我来说下HINT是什么，在什么时候用。
HINT简单来说就是在某些特定的场景下人工协助MySQL优化器的工作，使她生成最优的执行计划。一般来说，优化器的执行计划都是最优化的，不过在某些特定场景下，执行计划可能不是最优化。
比如：表t1经过大量的频繁更新 *** 作，（UPDATE,DELETE,INSERT），cardinality已经很不准确了，这时候刚好执行了一条SQL，那么有可能这条SQL的执行计划就不是最优的。为什么说有可能呢？
来看下具体演示
譬如，以下两条SQL，
A：
select * from t1 where f1 = 20B：
select * from t1 where f1 = 30如果f1的值刚好频繁更新的值为30，并且没有达到MySQL自动更新cardinality值的临界值或者说用户设置了手动更新又或者用户减少了sample page等等，那么对这两条语句来说，可能不准确的就是B了。
这里顺带说下，MySQL提供了自动更新和手动更新表cardinality值的方法，因篇幅有限，需要的可以查阅手册。
那回到正题上，MySQL 8.0 带来了几个HINT，我今天就举个index_merge的例子。
示例表结构：
mysql>desc t1+------------+--------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+------------+--------------+------+-----+---------+----------------+| id | int(11) | NO | PRI | NULL | auto_increment || rank1 | int(11) | YES | MUL | NULL | || rank2 | int(11) | YES | MUL | NULL | || log_time | datetime | YES | MUL | NULL | || prefix_uid | varchar(100) | YES | | NULL | || desc1 | text | YES | | NULL | || rank3 | int(11) | YES | MUL | NULL | |+------------+--------------+------+-----+---------+----------------+7 rows in set (0.00 sec)表记录数：
mysql>select count(*) from t1+----------+| count(*) |+----------+| 32768 |+----------+1 row in set (0.01 sec)这里我们两条经典的SQL：
SQL C：
select * from t1 where rank1 = 1 or rank2 = 2 or rank3 = 2SQL D：
select * from t1 where rank1 =100 and rank2 =100 and rank3 =100表t1实际上在rank1,rank2,rank3三列上分别有一个二级索引。
那我们来看SQL C的查询计划。
显然，没有用到任何索引，扫描的行数为32034，cost为3243.65。
mysql>explain format=json select * from t1 where rank1 =1 or rank2 = 2 or rank3 = 2\G*************************** 1. row ***************************EXPLAIN: { "query_block": { "select_id": 1, "cost_info": { "query_cost": "3243.65" }, "table": { "table_name": "t1", "access_type": "ALL", "possible_keys": [ "idx_rank1", "idx_rank2", "idx_rank3" ], "rows_examined_per_scan": 32034, "rows_produced_per_join": 115, "filtered": "0.36", "cost_info": { "read_cost": "3232.07", "eval_cost": "11.58", "prefix_cost": "3243.65", "data_read_per_join": "49K" }, "used_columns": [ "id", "rank1", "rank2", "log_time", "prefix_uid", "desc1", "rank3" ], "attached_condition": "((`ytt`.`t1`.`rank1` = 1) or (`ytt`.`t1`.`rank2` = 2) or (`ytt`.`t1`.`rank3` = 2))" } }}1 row in set, 1 warning (0.00 sec)我们加上hint给相同的查询，再次看看查询计划。
这个时候用到了index_merge,union了三个列。扫描的行数为1103，cost为441.09，明显比之前的快了好几倍。
mysql>explain format=json select /*+ index_merge(t1) */ * from t1 where rank1 =1 or rank2 = 2 or rank3 = 2\G*************************** 1. row ***************************EXPLAIN: { "query_block": { "select_id": 1, "cost_info": { "query_cost": "441.09" }, "table": { "table_name": "t1", "access_type": "index_merge", "possible_keys": [ "idx_rank1", "idx_rank2", "idx_rank3" ], "key": "union(idx_rank1,idx_rank2,idx_rank3)", "key_length": "5,5,5", "rows_examined_per_scan": 1103, "rows_produced_per_join": 1103, "filtered": "100.00", "cost_info": { "read_cost": "330.79", "eval_cost": "110.30", "prefix_cost": "441.09", "data_read_per_join": "473K" }, "used_columns": [ "id", "rank1", "rank2", "log_time", "prefix_uid", "desc1", "rank3" ], "attached_condition": "((`ytt`.`t1`.`rank1` = 1) or (`ytt`.`t1`.`rank2` = 2) or (`ytt`.`t1`.`rank3` = 2))" } }}1 row in set, 1 warning (0.00 sec)我们再看下SQL D的计划：
不加HINT，
mysql>explain format=json select * from t1 where rank1 =100 and rank2 =100 and rank3 =100\G*************************** 1. row ***************************EXPLAIN: { "query_block": { "select_id": 1, "cost_info": { "query_cost": "534.34" }, "table": { "table_name": "t1", "access_type": "ref", "possible_keys": [ "idx_rank1", "idx_rank2", "idx_rank3" ], "key": "idx_rank1", "used_key_parts": [ "rank1" ], "key_length": "5", "ref": [ "const" ], "rows_examined_per_scan": 555, "rows_produced_per_join": 0, "filtered": "0.07", "cost_info": { "read_cost": "478.84", "eval_cost": "0.04", "prefix_cost": "534.34", "data_read_per_join": "176" }, "used_columns": [ "id", "rank1", "rank2", "log_time", "prefix_uid", "desc1", "rank3" ], "attached_condition": "((`ytt`.`t1`.`rank3` = 100) and (`ytt`.`t1`.`rank2` = 100))" } }}1 row in set, 1 warning (0.00 sec)加了HINT，
mysql>explain format=json select /*+ index_merge(t1)*/ * from t1 where rank1 =100 and rank2 =100 and rank3 =100\G*************************** 1. row ***************************EXPLAIN: { "query_block": { "select_id": 1, "cost_info": { "query_cost": "5.23" }, "table": { "table_name": "t1", "access_type": "index_merge", "possible_keys": [ "idx_rank1", "idx_rank2", "idx_rank3" ], "key": "intersect(idx_rank1,idx_rank2,idx_rank3)", "key_length": "5,5,5", "rows_examined_per_scan": 1, "rows_produced_per_join": 1, "filtered": "100.00", "cost_info": { "read_cost": "5.13", "eval_cost": "0.10", "prefix_cost": "5.23", "data_read_per_join": "440" }, "used_columns": [ "id", "rank1", "rank2", "log_time", "prefix_uid", "desc1", "rank3" ], "attached_condition": "((`ytt`.`t1`.`rank3` = 100) and (`ytt`.`t1`.`rank2` = 100) and (`ytt`.`t1`.`rank1` = 100))" } }}1 row in set, 1 warning (0.00 sec)对比下以上两个，加了HINT的比不加HINT的cost小了100倍。
总结下，就是说表的cardinality值影响这张的查询计划，如果这个值没有正常更新的话，就需要手工加HINT了。相信MySQL未来的版本会带来更多的HINT。
mysql ndbcluster 安装1.数据库规划：
*** 作系统 centos 6.3
ndbcluster 版本：MySQL-Cluster-gpl-7.4.8-1.el6.x86_64
2个管理节点、2个sql节点、2个数据节点（管理节点和sql节点放在同一台服务器上）
如下：
管理节点1 192.168.1.17
管理节点2 192.168.1.18
sql节点1 192.168.1.17
sql节点2 192.168.1.18
ndbd 节点1 192.168.1.19
ndbd 节点2 192.168.1.20
2. *** 作系统设置：
设置服务主机名称
关闭selinux和防火墙
设置内核参数和最大进程数
下载mysql集群
MySQL-Cluster-gpl-7.4.8-1.el6.x86_64.rpm-bundle.tar
上传到服务器的相应目录下如 /home/mysqlinstall
3.安装管理节点和sql节点：
To check if your system has any RPM version of any MySQL package currently installed, run:
shell>rpm -qa | grep -i mysql
检查
[root@redis1 ~]# rpm -qa | grep -i mysql
mysql-libs-5.1.61-4.el6.x86_64
如果有删除
shell>rpm -e mysql-libs-5.1.61-4.el6.x86_64
删除报错：
[root@redis1 ~]# rpm -e mysql-libs-5.1.61-4.el6.x86_64
error: Failed dependencies:
libmysqlclient.so.16()(64bit) is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64
libmysqlclient.so.16(libmysqlclient_16)(64bit) is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64
mysql-libs is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64
[root@redis1 ~]#
解决：
[root@redis1 ~]# rpm -e --nodeps mysql-libs-5.1.61-4.el6.x86_64
[root@redis1 ~]#
[root@ndbcluster1 mysqlinstall]# rpm -ivh MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm
[root@ndbcluster1 mysqlinstall]# rpm -ivh MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm
4.安装数据节点：
执行上面步骤
[root@ndb mysqlinstall]# rpm -ivh MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm
[root@ndb mysqlinstall]# rpm -ivh MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm
5.配置集群
管理节点建立目录
mkdir /var/lib/mysql-cluster
mkdir -p /data/mysql/ndbdata
5.启动关闭集群：
启动管理节点
ndb_mgmd -f /var/lib/mysql-cluster/config.ini --initial (第一次启动加--initial修改了配置文件后的启动)
启动数据节点
ndbmtd --initial
启动sql节点
service mysql start
查看集群状态
shell>ndb_mgm -e "SHOW"
关闭管理节点和数据节点
ndb_mgm -e shutdown
关闭sql节点
service mysql stop
安装遇到的问题：
1.权限问题启动mysql报错
[root@sqlmgm2 mysql]# service mysql start
Starting MySQL..The server quit without updating PID file ([FAILED]sql/sqlmgm2.pid).
[root@sqlmgm2 mysql]#
[root@sqlmgm2 mysql]# ll
total 110644
-rw-rw---- 1 mysql mysql 56 Dec 14 17:13 auto.cnf
-rw-rw---- 1 mysql mysql 12582912 Dec 14 17:39 ibdata1
-rw-rw---- 1 mysql mysql 50331648 Dec 14 17:40 ib_logfile0
-rw-rw---- 1 mysql mysql 50331648 Dec 14 17:13 ib_logfile1
drwx------ 2 mysql mysql 4096 Dec 14 17:39 mysql
drwx------ 2 root root 4096 Dec 14 17:39 ndbinfo
drwx------ 2 root root 4096 Dec 14 17:39 performance_schema
-rw-r----- 1 mysql mysql30068 Dec 14 17:40 sqlmgm2.err
drwx------ 2 root root 4096 Dec 14 17:33 test
[root@sqlmgm2 mysql]# chown mysql:mysql -R mysql
[root@sqlmgm2 mysql]# service mysql start
Starting MySQL.. [ OK ]
[root@sqlmgm2 mysql]#
2.安装rpm包时，报包依赖关系如下：
[root@ndbcluster2 mysqlinstall]# rpm -ivh MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm
warning: MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64.rpm: Header V3 DSA/SHA1 Signature, key ID 5072e1f5: NOKEY
error: Failed dependencies:
libnuma.so.1()(64bit) is needed by MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64
libnuma.so.1(libnuma_1.1)(64bit) is needed by MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64
libnuma.so.1(libnuma_1.2)(64bit) is needed by MySQL-Cluster-server-gpl-7.4.8-1.el6.x86_64
解决方法是把安装的依赖的包
[root@ndbcluster2 mysqlinstall]# yum install numactl
Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
* base: mirrors.163.com
* extras: mirrors.opencas.cn
* updates: mirrors.opencas.cn
Setting up Install Process
Resolving Dependencies
-->Running transaction check
--->Package numactl.x86_64 0:2.0.9-2.el6 will be installed
-->Finished Dependency Resolution
Dependencies Resolved
==============================================================================================================================
Package ArchVersion Repository Size
==============================================================================================================================
Installing:
numactl x86_64 2.0.9-2.el6 base 74 k
Transaction Summary
==============================================================================================================================
Install 1 Package(s)
Total download size: 74 k
Installed size: 171 k
Is this ok [y/N]: y
Downloading Packages:
numactl-2.0.9-2.el6.x86_64.rpm | 74 kB 00:00
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA1 Signature, key ID c105b9de: NOKEY
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Importing GPG key 0xC105B9DE:
Userid : CentOS-6 Key (CentOS 6 Official Signing Key) <centos-6-key@centos.org>
Package: centos-release-6-3.el6.centos.9.x86_64 (@anaconda-CentOS-201207061011.x86_64/6.3)
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Is this ok [y/N]: y
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : numactl-2.0.9-2.el6.x86_64 1/1
Verifying : numactl-2.0.9-2.el6.x86_64 1/1
Installed:
numactl.x86_64 0:2.0.9-2.el6
Complete!
3.启动数据库节点无法和管理节点相连
原因由于防火墙和selinux没有关闭
解决关闭防火墙和selinux
一、关闭防火墙
1、重启后永久性生效：
开启：chkconfig iptables on
关闭：chkconfig iptables off
2、即时生效，重启后失效：
开启：service iptables start
关闭：service iptables stop
二、关闭SELinux
vim /etc/selinux/config # 改为 SELINUX=disabled
# 保存退出，重启服务器
init 6
禁用SeLinux
#永久禁用，需要重启生效。
sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config
# 临时禁用，不需要重启
setenforce 0
4.root用户不能登录
[root@ndbcluster2 ~]# mysql -uroot -p
Enter password:
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@ndbcluster2 ~]# mysql -uroot -p
Enter password:
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
设置--skip-grant-tables跳过授权表认证
service mysqld stop
在配置文件中添加--skip-grant-tables（/etc/my.cnf）
service mysqld start
另外开个SSH连接
[root@localhost ~]# mysql
mysql>use mysql
mysql>update user set password=password("123456") where user="root"
mysql>flush privileges
mysql>exit
去掉--skip-grant-tables重启mysql,root用户可以用设置的密码登录
设置root用户远程登录
GRANT ALL PRIVILEGES ON *.* TO root@'%' IDENTIFIED BY '123456' WITH GRANT OPTION
执行报如下错误，ERROR 1820 (HY000): You must SET PASSWORD before executing this statement
[root@ndbcluster1 ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with or \g.
Your MySQL connection id is 2
Server version: 5.6.27-ndb-7.4.8-cluster-gpl
Copyright (c) 2000, 2015, 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.
mysql>
mysql>
mysql>GRANT ALL PRIVILEGES ON *.* TO root@"%" IDENTIFIED BY 'root' WITH GRANT OPTION
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement
mysql>GRANT ALL PRIVILEGES ON *.* TO root@"%" IDENTIFIED BY 'root001' WITH GRANT OPTION
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement
执行SET PASSWORD修改成功
mysql>SET PASSWORD = PASSWORD('root001')
Query OK, 0 rows affected (0.02 sec)
mysql> GRANT ALL PRIVILEGES ON *.* TO root@"%" IDENTIFIED BY 'root' WITH GRANT OPTION
Query OK, 0 rows affected (0.02 sec)
mysql>
FLUSH PRIVILEGES
执行完成
远程连接测试，mysql集群节点，发现一个节点可以连接，一个节点不能连接
这个问题纠结很久
原因上面的 *** 作，没有在另外一个节点上执行导致的，mysql集群的用户认证是分开管理的，要两个节点都要执行
索引以后创建用户要两个节点都执行
5.配置两个管理节点时show报错Could not get configuration
[root@ndbcluster2 mysql-cluster]# ndb_mgm
-- NDB Cluster -- Management Client --
ndb_mgm>show
Connected to Management Server at: 192.168.1.17:1186
ERROR Message: The cluster configuration is not yet confirmed by all defined management servers. This management server is still waiting for node 6 to connect.
Could not get configuration
* 4012: Failed to get configuration
*The cluster configuration is not yet confirmed by all defined management servers. This management server is still waiting for node 6 to connect.
ndb_mgm>show
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=2 (not connected, accepting connect from 192.168.1.18)
id=3 (not connected, accepting connect from 192.168.1.17)
[ndb_mgmd(MGM)] 2 node(s)
id=1@192.168.1.17 (mysql-5.6.27 ndb-7.4.8)
id=6@192.168.1.18 (mysql-5.6.27 ndb-7.4.8)
[mysqld(API)] 2 node(s)
id=4 (not connected, accepting connect from 192.168.1.17)
id=5 (not connected, accepting connect from 192.168.1.18)
两个管理节点同时都启动起来，才能看到状态
ndb_mgm>show
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=2@192.168.1.18 (mysql-5.6.27 ndb-7.4.8, Nodegroup: 0, *)
id=3@192.168.1.17 (mysql-5.6.27 ndb-7.4.8, Nodegroup: 0)
[ndb_mgmd(MGM)] 2 node(s)
id=1@192.168.1.17 (mysql-5.6.27 ndb-7.4.8)
id=6@192.168.1.18 (mysql-5.6.27 ndb-7.4.8)
[mysqld(API)] 2 node(s)
id=4@192.168.1.17 (mysql-5.6.27 ndb-7.4.8)
id=5@192.168.1.18 (mysql-5.6.27 ndb-7.4.8)
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