前面的文章简单的介绍了ClickHouse，以及也进行了简单的性能测试。本次说说集群的搭建以及数据复制，如果复制数据需要zookeeper配合。
环境：
1. 3台机器，我这里是3台虚拟机。都安装了clickhouse。
2. 绑定hosts，其实不绑定也没关系，配置文件里面直接写ip。（3台机器都绑定hosts，如下）
192.168.0.10 db_server_yayun_01 192.168.0.20 db_server_yayun_02 192.168.0.30 db_server_yayun_03
3. 创建配置文件，默认这个配置文件是不存在的。/etc/clickhouse-server/config.xml有提示，如下：
If element has 'incl' attribute, then for it's value will be used corresponding substitution from another file.
By default, path to file with substitutions is /etc/metrika.xml. It could be changed in config in 'include_from' element.
Values for substitutions are specified in /yandex/name_of_substitution elements in that file.
配置文件/etc/metrika.xml内容如下：
true db_server_yayun_01 9000 true db_server_yayun_02 9000 true db_server_yayun_03 9000 "1"> 192.168.0.30 2181 192.168.0.10 ::/0
10000000000 0.01 lz4
3台机器的配置文件都一样，唯一有区别的是：
192.168.0.10
服务器ip是多少这里就写多少，其实不写ip也没关系，3台机器不重复就行。这里是复制需要用到的配置。还有zk的配置如下：
"1"> 192.168.0.30 2181
我的zk是安装在30的机器上面的，只安装了一个实例，生产环境肯定要放到单独的机器，并且配置成集群。配置文件修改好以后3台服务器重启。
官方文档给的步骤是：
ClickHouse deployment to cluster ClickHouse cluster is a homogenous cluster. Steps to set up: 1. Install ClickHouse server on all machines of the cluster 2. Set up cluster configs in configuration file 3. Create local tables on each instance 4. Create a Distributed table
前面2步都搞定了，下面创建本地表，再创建Distributed表。（3台机器都创建，DDL不同步，蛋疼）
CREATE TABLE ontime_local (FlightDate Date,Year UInt16) ENGINE = MergeTree(FlightDate, (Year, FlightDate), 8192); CREATE TABLE ontime_all AS ontime_local ENGINE = Distributed(perftest_3shards_1replicas, default, ontime_local, rand())
插入数据（随便一台机器就行）：
:) insert into ontime_all (FlightDate,Year)values('2001-10-12',2001); INSERT INTO ontime_all (FlightDate, Year) VALUES Ok. 1 rows in set. Elapsed: 0.013 sec. :) insert into ontime_all (FlightDate,Year)values('2002-10-12',2002); INSERT INTO ontime_all (FlightDate, Year) VALUES Ok. 1 rows in set. Elapsed: 0.004 sec. :) insert into ontime_all (FlightDate,Year)values('2003-10-12',2003); INSERT INTO ontime_all (FlightDate, Year) VALUES Ok.
我这里插入了3条数据。下面查询看看（任何一台机器都可以）：
:) select * from ontime_all; SELECT * FROM ontime_all ┌─FlightDate─┬─Year─┐ │ 2001-10-12 │ 2001 │ └────────────┴──────┘ ┌─FlightDate─┬─Year─┐ │ 2002-10-12 │ 2002 │ └────────────┴──────┘ ┌─FlightDate─┬─Year─┐ │ 2003-10-12 │ 2003 │ └────────────┴──────┘ → Progress: 3.00 rows, 12.00 B (48.27 rows/s., 193.08 B/s.) 3 rows in set. Elapsed: 0.063 sec. :)
当在其中一台机器上面查询的时候，抓包其他机器可以看见是有请求的。
tcpdump -i any -s 0 -l -w - dst port 9000
那么关闭其中一台机器呢？
:) select * from ontime_all; SELECT * FROM ontime_all ┌─FlightDate─┬─Year─┐ │ 2001-10-12 │ 2001 │ └────────────┴──────┘ ┌─FlightDate─┬─Year─┐ │ 2002-10-12 │ 2002 │ └────────────┴──────┘ ┌─FlightDate─┬─Year─┐ │ 2003-10-12 │ 2003 │ └────────────┴──────┘ ↓ Progress: 6.00 rows, 24.00 B (292.80 rows/s., 1.17 KB/s.) Received exception from server: Code: 279. DB::Exception: Received from localhost:9000, ::1. DB::NetException. DB::NetException: All connection tries failed. Log: Code: 210, e.displayText() = DB::NetException: Connection refused: (db_server_yayun_02:9000, 192.168.0.20), e.what() = DB::NetException Code: 210, e.displayText() = DB::NetException: Connection refused: (db_server_yayun_02:9000, 192.168.0.20), e.what() = DB::NetException Code: 210, e.displayText() = DB::NetException: Connection refused: (db_server_yayun_02:9000, 192.168.0.20), e.what() = DB::NetException
可以看见已经抛错了，竟然不是高可用？后面又看到了文档的另外一种配置方法，那就是配置2个节点，副本2个，经过测试高可用没有问题，另外也是分布式并行查询。感兴趣的同学可以自行测试。
https://clickhouse.yandex/reference_en.html#Distributed
下面进行数据复制的测试,zk已经配置好了，直接建表测试（3台机器都创建）：
CREATE TABLE ontime_replica (FlightDate Date,Year UInt16) ENGINE = ReplicatedMergeTree('/clickhouse_perftest/tables/ontime_replica','{replica}',FlightDate,(Year, FlightDate),8192);
插入数据测试：
insert into ontime_replica (FlightDate,Year)values('2018-10-12',2018);
任何一台机器均可查询到。其实到现在对于集群和复制都还没彻底搞明白，因为分布式表也进行了数据复制，所以有点懵。有大婶的话欢迎一起交流。
参考资料：
https://clickhouse.yandex/reference_en.html#Distributed
https://clickhouse.yandex/tutorial.html