MaterializeMySQL  简介

MySQL 的用户群体很大，为了能够增强数据的实时性，很多解决方案会利用 binlog 将数据写入到 ClickHouse。为了能够监听 binlog 事件，我们需要用到类似 canal 这样的第三方中间件，这无疑增加了系统的复杂度。

ClickHouse 20.8.2.3版本新增加了 MaterializeMySQL 的 database 引擎，该 database 能映射到 MySQL 中的某个 database，并自动在 ClickHouse 中创建对应的 ReplacingMergeTree。ClickHouse服务做为MySQL副本，读取Binlog并执行DDL和DML请求，实现了基于MySQL Binlog机制的业务数据库实时同步功能。

版本说明

ClickHouse 版本：21.7.3.14-2.

MySql 版本 5.7.16

my.cnf 配置

#数据库id
server-id = 1
##启动binlog，该参数的值会作为binlog的文件名
log-bin=mysql-bin
##binlog类型，maxwell要求为row类型
binlog_format=ROW
gtid-mode=on
# 设置为主从强一致性
enforce-gtid-consistency=1 
# 记录日志
log-slave-updates=1   

问题场景

今天在测试 MaterializeMySQL  功能的时候除出现了一个现象，ClickHouse中创建  MaterializeMySQL 数据库后，ClickHouse数据库建立后，表没有同步到ClickHouse，检查了一下 my.cnf 配置信息，和ClickHouse同步信息，都没有问题；查看日之后发一个问题；

[root@hadoop201 hui]# tail -f /var/log/clickhouse-server/clickhouse-server.err.log  

2022.08.06 12:18:23.930444 [ 2640 ] {} <Error> MaterializeMySQLSyncThread: Code: 48, e.displayText() = DB::Exception: The test.book_info cannot be materialized, because there is no primary keys.: While executing dump MySQL test.book_info table data., Stack trace (when copying this message, always include the lines below):

0. DB::Exception::Exception(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int, bool) @ 0x8d31b5a in /usr/bin/clickhouse
1. DB::MySQLInterpreter::InterpreterCreateImpl::getRewrittenQueries(DB::MySQLParser::ASTCreateQuery const&, std::__1::shared_ptr<DB::Context const>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) @ 0xfe4d726 in /usr/bin/clickhouse
2. DB::MySQLInterpreter::InterpreterMySQLDDLQuery<DB::MySQLInterpreter::InterpreterCreateImpl>::execute() @ 0xfaafbdb in /usr/bin/clickhouse
3. DB::InterpreterExternalDDLQuery::execute() @ 0xfaade78 in /usr/bin/clickhouse
4. ? @ 0xfe22253 in /usr/bin/clickhouse
5. DB::executeQuery(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::shared_ptr<DB::Context>, bool, DB::QueryProcessingStage::Enum, bool) @ 0xfe208e3 in /usr/bin/clickhouse
6. ? @ 0xf7ba406 in /usr/bin/clickhouse
7. ? @ 0xf7d4b88 in /usr/bin/clickhouse
8. DB::commitMetadata(std::__1::function<void ()> const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) @ 0xf807632 in /usr/bin/clickhouse
9. DB::MaterializeMetadata::transaction(DB::MySQLReplication::Position const&, std::__1::function<void ()> const&) @ 0xf80a000 in /usr/bin/clickhouse
10. DB::MaterializeMySQLSyncThread::prepareSynchronized(DB::MaterializeMetadata&) @ 0xf7b2231 in /usr/bin/clickhouse
11. DB::MaterializeMySQLSyncThread::synchronization() @ 0xf7b169c in /usr/bin/clickhouse
12. ? @ 0xf7d4074 in /usr/bin/clickhouse
13. ThreadPoolImpl<std::__1::thread>::worker(std::__1::__list_iterator<std::__1::thread, void*>) @ 0x8d72a1f in /usr/bin/clickhouse
14. ? @ 0x8d76303 in /usr/bin/clickhouse
15. start_thread @ 0x7ea5 in /usr/lib64/libpthread-2.17.so
16. __clone @ 0xfe9fd in /usr/lib64/libc-2.17.so

好像是说 MySQL 的表没设置主键，之前的建表语句

 CREATE TABLE `book_info` (
  `id` INT(11)  ,
  `name` VARCHAR(20) COLLATE utf8_german2_ci DEFAULT NULL,
  `author` VARCHAR(20) COLLATE utf8_german2_ci DEFAULT NULL
  ) ENGINE=INNODB DEFAULT CHARSET=utf8 COLLATE=utf8_german2_ci

确实没有设置主键，删表重建下

drop table test.book_info;
CREATE TABLE `book_info`
(
    `id`     INT(11),
    `name`   VARCHAR(20) COLLATE utf8_german2_ci DEFAULT NULL,
    `author` VARCHAR(20) COLLATE utf8_german2_ci DEFAULT NULL,
    PRIMARY KEY (`id`)
) ENGINE = INNODB
  DEFAULT CHARSET = utf8
  COLLATE = utf8_german2_ci

插入数据

INSERT INTO `book_info` (`id`, `name`, `author`)
VALUES ('1001', '侠客行', '金庸');
INSERT INTO `book_info` (`id`, `name`, `author`)
VALUES ('1002', '孔雀翎', '古龙');
INSERT INTO `book_info` (`id`, `name`, `author`)
VALUES ('1003', '萍踪侠影', '梁羽生');
commit;

此时回到 ClickHouse ,把刚才建的数据库删了，重新建一下

drop database test_binlog;
set allow_experimental_database_materialize_mysql=1;
CREATE DATABASE test_binlog ENGINE =  MaterializeMySQL('hadoop201:3306','test','root','mypwd');

现在查看 ClickHouse 下的表已经有了

select * from test_binlog.book_info

1002 孔雀翎 古龙
1003 萍踪侠影 梁羽生
1001 侠客行 金庸

现在更新一下Mysql 里的数据

UPDATE book_info SET NAME = '侠客行-1980' WHERE id = '1001';
COMMIT;
SELECT *
FROM book_info;
1001    侠客行-1980    金庸
1002    孔雀翎    古龙
1003    萍踪侠影    梁羽生

查看ClickHouse  结果

select * from test_binlog.book_info
1002    孔雀翎    古龙
1003    萍踪侠影    梁羽生
1001    侠客行-1980    金庸

至此：问题得以解决。