目前CDC（Change Data Capture）工具还是比较多的 ，现在有部分增量数据同步工具是基于触发器实现的，把数据库的变化记录到某个系统表中，然后在客户端建立缓冲，并定期将变化push到接收端，接收端和发送端建立通道，并定期pull新的数据变化，在目标数据库回放 。但因为使用了触发器会影响生产环境的性能，这点可能无法接受 ，其他的增量数据同步工具中占比比较大的一类，是基于kafka来实现的。例如RedHat开源的 Debezium。通过抽取数据库日志来获取变更，实现增量数据同步。下面是一个PostgreSQL数据同步至kafka 的例子：

一、准备java环境

[root@ysla bin]# yum install java-1.8.0-openjdk.x86_64
[root@ysla bin]# yum install java-1.8.0-openjdk-devel.x86_64
[root@ysla bin]# java -version
openjdk version "1.8.0_322"
OpenJDK Runtime Environment (build 1.8.0_322-b06)
OpenJDK 64-Bit Server VM (build 25.322-b06, mixed mode)

二、启动zookeeper

[root@ysla ~]# tar -xf apache-zookeeper-3.8.0-bin.tar.gz
[root@ysla ~]# cd apache-zookeeper-3.8.0-bin/
[root@ysla apache-zookeeper-3.8.0-bin]# ls
bin  conf  docs  lib  LICENSE.txt  NOTICE.txt  README.md  README_packaging.md
[root@ysla apache-zookeeper-3.8.0-bin]# cd conf/
[root@ysla conf]# ls
configuration.xsl  logback.xml  zoo_sample.cfg
[root@ysla conf]# cp zoo_sample.cfg  zoo.cfg

[root@ysla bin]# pwd
/root/apache-zookeeper-3.8.0-bin/bin
[root@ysla bin]# ./zkServer.sh start
/bin/java
ZooKeeper JMX enabled by default
Using config: /root/apache-zookeeper-3.8.0-bin/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED
[root@ysla bin]# jps
65408 Jps
65355 QuorumPeerMain

可以使用zkCli.sh进行连接测试

[root@ysla bin]# ./zkCli.sh -server 127.0.0.1:2181

三、启动kafka

[root@ysla ~]# tar -xf kafka_2.13-3.1.0.tgz
[root@ysla ~]# cd kafka_2.13-3.1.0/
[root@ysla kafka_2.13-3.1.0]# ls
bin  config  libs  LICENSE  licenses  NOTICE  site-docs

因为我zookeeper也安在本地，所以server.properties不用修改，走的localhost

[root@ysla bin]# ./kafka-server-start.sh ../config/server.properties &

[root@ysla bin]# jps
74677 Kafka
75227 Jps
65355 QuorumPeerMain

四、安装kafkacat

安装依赖

[root@ysla kafkacat]# yum install -y librdkafka-devel

安装kafkacat

[root@ysla ~]# git clone https://github.com/edenhill/kafkacat
Cloning into 'kafkacat'...
remote: Enumerating objects: 1550, done.
remote: Counting objects: 100% (280/280), done.
remote: Compressing objects: 100% (177/177), done.
remote: Total 1550 (delta 157), reused 195 (delta 93), pack-reused 1270
Receiving objects: 100% (1550/1550), 627.51 KiB | 221.00 KiB/s, done.
Resolving deltas: 100% (935/935), done.

[root@ysla ~]# cd kafkacat
[root@ysla kafkacat]# ./configure
[root@ysla kafkacat]# make -j 24
[root@ysla kafkacat]# make install -j 24

[root@ysla kafkacat]# kcat --help
Usage: kcat <options> [file1 file2 .. | topic1 topic2 ..]]
kcat - Apache Kafka producer and consumer tool
https://github.com/edenhill/kcat
Copyright (c) 2014-2021, Magnus Edenhill
Version 1.7.1-2-g338ae3 (librdkafka 0.11.4 builtin.features=gzip,snappy,ssl,sasl,regex,lz4,sasl_gssapi,sasl_plain,sasl_scram,plugins)


General options:
  -C | -P | -L | -Q  Mode: Consume, Produce, Metadata List, Query mode
  -G <group-id>      Mode: High-level KafkaConsumer (Kafka >=0.9 balanced consumer groups)
                     Expects a list of topics to subscribe to
  -t <topic>         Topic to consume from, produce to, or list
  -p <partition>     Partition
  -b <brokers,..>    Bootstrap broker(s) (host[:port])
  -D <delim>         Message delimiter string:
                     a-z | \r | \n | \t | \xNN ..
                     Default: \n
  -K <delim>         Key delimiter (same format as -D)
  -c <cnt>           Limit message count
  -m <seconds>       Metadata (et.al.) request timeout.
                     This limits how long kcat will block
                     while waiting for initial metadata to be
                     retrieved from the Kafka cluster.
                     It also sets the timeout for the producer's
                     transaction commits, init, aborts, etc.
                     Default: 5 seconds.

五、数据库安装wal2json

我的下载地址为
Release wal2json 2.3 · eulerto/wal2json · GitHub

[root@ysla local]# tar -xf wal2json-wal2json_2_3.tar.gz
[root@ysla wal2json-wal2json_2_3]# chown -R postgres: wal2json-wal2json_2_3/
[root@ysla local]# su - postgres
Last login: Wed Mar 23 15:52:23 CST 2022 on pts/1
[postgres@ysla ~]$ cd /usr/local/wal2json-wal2json_2_3/
[postgres@ysla wal2json-wal2json_2_3]$ ls
expected  LICENSE  Makefile  README.md  sql  wal2json.c  wal2json.vcxproj

[postgres@ysla local]$ export PATH=/opt/pg12/bin/pg_config:$PATH
[postgres@ysla local]$ make -j 24
make: *** No targets specified and no makefile found.  Stop.
[postgres@ysla local]$ ls
bin  etc  games  include  lib  lib64  libexec  psql  sbin  share  src  wal2json-wal2json_2_3  wal2json-wal2json_2_3.tar.gz
[postgres@ysla local]$ cd wal2json-wal2json_2_3/
[postgres@ysla wal2json-wal2json_2_3]$ make -j 24
gcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -fPIC -I. -I./ -I/opt/pg12/include/postgresql/server -I/opt/pg12/include/postgresql/internal  -D_GNU_SOURCE   -c -o wal2json.o wal2json.c
gcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -O2 -fPIC wal2json.o -L/opt/pg12/lib   -Wl,--as-needed -Wl,-rpath,'/opt/pg12/lib',--enable-new-dtags  -shared -o wal2json.so
[postgres@ysla wal2json-wal2json_2_3]$ make install -j 24
/bin/mkdir -p '/opt/pg12/lib/postgresql'
/bin/install -c -m 755  wal2json.so '/opt/pg12/lib/postgresql/'
[postgres@ysla wal2json-wal2json_2_3]$ ls
expected  LICENSE  Makefile  README.md  sql  wal2json.c  wal2json.o  wal2json.so  wal2json.vcxproj
[postgres@ysla wal2json-wal2json_2_3]$ ll /opt/pg12/lib/postgresql/wal2json.so
-rwxr-xr-x 1 postgres dba 49224 Mar 23 16:01 /opt/pg12/lib/postgresql/wal2json.so

postgresql.conf里添加shared_preload_libraries = 'wal2json.so’并修改wal_level = logical，之后重启数据库

六、造测试数据并消费

创建复制槽

[postgres@ysla ~]$ /opt/pg12/bin/pg_recvlogical -d postgres --slot slot1 --create-slot -P wal2json

[postgres@ysla ~]$ psql -c "select * from pg_replication_slots;"
 slot_name |  plugin  | slot_type | datoid | database | temporary | active | active_pid | xmin | catalog_xmin | restart_lsn | confirmed_flush_lsn
-----------+----------+-----------+--------+----------+-----------+--------+------------+------+--------------+-------------+---------------------
 slot1     | wal2json | logical   |  13593 | postgres | f         | f      |            |      |          855 | 0/2A03FE20  | 0/2A03FE58
(1 row)

我这里为了方便使用本地postgres用户。如有需求，按这样创建用户CREATE ROLR uysl WITH REPLICATION PASSWORD ‘QAZqaz123’ LOGIN;并修改pg_hba.conf，使该用户可以远程或本地访问数据库。

创建测试表

CREATE TABLE test_table (
    id char(10) NOT NULL,
    code        char(10),
    PRIMARY KEY (id)
);

开启一个终端，生产数据到本地 kafka

[root@ysla ~]# /opt/pg12/bin/pg_recvlogical -h localhost -p 6000 -U postgres   -d postgres -S slot1 --start -f - | /root/kafkacat/kcat -b 172.20.10.3:9092 -t testdb_topic
% Auto-selecting Producer mode (use -P or -C to override)

消费testdb_topic

[root@ysla kafka_2.13-3.1.0]# pwd
/root/kafka_2.13-3.1.0
[root@ysla kafka_2.13-3.1.0]# bin/kafka-console-consumer.sh --topic testdb_topic --bootstrap-server 172.20.10.3:9092 --from-beginning