【原理】MySQL主从复制之增强半同步（无损复制）、延迟复制和并行复制
简介
MySQL主从复制过程：
主从复制方式
MySQL有四种同步方式：
1、异步复制（Async Replication）
2、同步复制（sync Replication）
3、半同步复制（Async Replication）
4、增强半同步复制（lossless Semi-Sync Replication）、无损复制
1、异步复制（Async Replication）
主库将更新写入Binlog日志文件后，不需要等待数据更新是否已经复制到从库中，就可以继续处理更多的请求。Master将事件写入binlog，但并不知道Slave是否或何时已经接收且已处理。在异步复制的机制的情况下，如果Master宕机，事务在Master上已提交，但很可能这些事务没有传到任何的Slave上。假设有Master->Salve故障转移的机制，此时Slave也可能会丢失事务。MySQL复制默认是异步复制，异步复制提供了最佳性能。
2、同步复制（Sync Replication）
主库将更新写入Binlog日志文件后，需要等待数据更新已经复制到从库中，并且已经在从库执行成功，然后才能返回继续处理其它的请求。同步复制提供了最佳安全性，保证数据安全，数据不会丢失，但对性能有一定的影响。
3、半同步复制（Semi-Sync Replication）
主库提交更新写入二进制日志文件后，等待数据更新写入了从服务器中继日志中，然后才能再继续处理其它请求。该功能确保至少有1个从库接收完主库传递过来的binlog内容已经写入到自己的relay log里面了，才会通知主库上面的等待线程，该操作完毕。
半同步复制，是最佳安全性与最佳性能之间的一个折中。
MySQL 5.5版本之后引入了半同步复制功能，主从服务器必须安装半同步复制插件，才能开启该复制功能。如果等待超时，超过rpl_semi_sync_master_timeout参数设置时间（默认值为10000，表示10秒），则关闭半同步复制，并自动转换为异步复制模式。当master dump线程发送完一个事务的所有事件之后，如果在rpl_semi_sync_master_timeout内，收到了从库的响应，则主从又重新恢复为增强半同步复制。
ACK (Acknowledge character）即是确认字符。
4、增强半同步复制（lossless Semi-Sync Replication、无损复制）
增强半同步是在MySQL 5.7引入，其实半同步可以看成是一个过渡功能，因为默认的配置就是增强半同步，所以，大家一般说的半同步复制其实就是增强的半同步复制，也就是无损复制。
增强半同步和半同步不同的是，等待ACK时间不同
rpl_semi_sync_master_wait_point = AFTER_SYNC（默认）
半同步的问题是因为等待ACK的点是Commit之后，此时Master已经完成数据变更，用户已经可以看到最新数据，当Binlog还未同步到Slave时，发生主从切换，那么此时从库是没有这个最新数据的，用户看到的是老数据。
增强半同步将等待ACK的点放在提交Commit之前，此时数据还未被提交，外界看不到数据变更，此时如果发送主从切换，新库依然还是老数据，不存在数据不一致的问题。
图示如下：
异步复制示例
MySQL主从复制之1主2从异步复制搭建及同步测试参考：https://www.xmmup.com/dbbao64mysqlzhucongzhi1zhu2congyibufuzhidajianjitongbuceshi.html
如何配置半同步复制
11.分别在主从安装插件 2 主： INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so'; 3 从： INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so'; 42.主服务器开启半同步 5 set global rpl_semi_sync_master_enabled=on; 63.从服务器开启半同步 7 set global rpl_semi_sync_slave_enabled=on; 8 94.配置主从同步（GTID模式示例）10server-id=1 （从为2，保证唯一性）11log-bin=master-bin 12log-bin-index=master-bin.index13binlog-format=ROW14gtid-mode=on15enforce-gtid-consistency=true延迟从库
延迟从库:从库落后于主库一段时间。
SQL线程延时:数据已经写入relaylog中了,只是让SQL线程”慢点”运行
MySQL延迟复制的好处主要有几点：
1.误删除时，能更快恢复数据。有时候手抖了，把线上数据给误删除了，或者误删除库、表、其他对象，或不加WHERE条件的更新、删除，都可以让延迟从库在误操作前的时间点停下，然后进行恢复。
2.把延迟从库作为专用的备份节点。虽然有一定的延迟，但并不影响利用该节点作为备份角色，也不影响生产节点数据库。
3.还可以把延迟从库当做一些问题、案例研究的对象。个别时候，可能有些Binlog Event在普通从库上会有问题（例如：早期版本中无主键会导致从库更新非常慢的经典问题），这时就有时间在延迟从库上慢慢琢磨研究了。
一般企业建议3-6小时，具体看公司运维人员对于故障的反应时间。
启用延迟从库的方法也挺简单的：
1#直接用CHANGE MASTER TO设置，后面的N单位是秒数：2STOP SLAVE SQL_THREAD;3CHANGE MASTER TO MASTER_DELAY = N;4START SLAVE SQL_THREAD;5查询：6show slave status\G7SQL_Delay: 0并行复制
MySQL 5.6提供了并行复制，但是这种并行只是基于database的（slave-parallel-type=DATABASE）。如果用户的MySQL数据库实例中存在多个database，对于从库复制的速度的确可以有比较大的帮助。如果是基于单个database的复制依然无法做到真正的并行回放，这个阶段很多DBA将数据库进行垂直拆分，将一个database拆分成几个database，通过设置slave_parallel_workers=n，可以进行database级别的并行复制，但对于热点业务复制延迟依然无法解决。参数slave_parallel_workers默认值为0，表示禁用并行。
到了MySQL 5.7，才实现了真正的并行复制（slave-parallel-type=LOGICAL_CLOCK），复制效率提升很多。MySQL 5.7的并行复制，multi-threaded slave即MTS，期望最大化还原主库的并行度，实现方式是在binlog event中增加必要的信息，以便slave节点根据这些信息实现并行复制。
要开启 MySQL 5.7 并行复制需要以下2步：
1、首先在主库设置 binlog_group_commit_sync_delay 的值大于0 。
1set global binlog_group_commit_sync_delay=10;2set global binlog_group_commit_sync_no_delay_count=10;binlog_group_commit_sync_delay 全局动态变量，单位微妙，默认0，范围：0～1000000（1秒）。
表示 binlog 提交后等待延迟多少时间再同步到磁盘，默认0 ，不延迟。当设置为 0 以上的时候，就允许多个事务的日志同时一起提交，也就是我们说的组提交。组提交是并行复制的基础，我们设置这个值的大于 0 就代表打开了组提交的功能。
binlog_group_commit_sync_no_delay_count 全局动态变量，单位个数，默认0，范围：0～1000000。
表示等待延迟提交的最大事务数，如果上面参数的时间没到，但事务数到了，则直接同步到磁盘。若 binlog_group_commit_sync_delay 没有开启，则该参数也不会开启。
2、其次要在 Slave 主机上设置如下几个参数：
1set global slave-parallel-type=LOGICAL_CLOCK;2set global slave-parallel-workers=16;一、1主2从之增强半同步复制（无损复制）示例
半同步复制比异步复制多了如下步骤：
1-- 1.分别在主从安装插件2 主： INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';3 从： INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';4-- 2.主服务器开启半同步5 set global rpl_semi_sync_master_enabled=on;6-- 3.从服务器开启半同步7 set global rpl_semi_sync_slave_enabled=on;1、MySQL环境初始化
1-- 设置主从的网络环境 2docker pull mysql:5.7.36 3docker network create --subnet=172.72.0.0/24 mysqln0 4 5 6-- 删除之前的容器 7docker rm -f MSS57M33650 MSS57S33651 MSS57S33652 8 9-- 创建参数文件路径 10mkdir -p /lhrmysqltest3/master/conf.d 11mkdir -p /lhrmysqltest3/slave1/conf.d 12mkdir -p /lhrmysqltest3/slave2/conf.d 13 14 15-- 申请主库环境 16docker run -d --name MSS57M33650 \ 17 -h master -p 33650:3306 --net=mysqln0 --ip 172.72.0.50 \ 18 -v /lhrmysqltest3/master/conf.d:/etc/mysql/conf.d \ 19 -e MYSQL_ROOT_PASSWORD=lhr \ 20 mysql:5.7.36 21 22-- 申请从库1环境 23docker run -d --name MSS57S33651 \ 24 -h slave1 -p 33651:3306 --net=mysqln0 --ip 172.72.0.51 \ 25 -v /lhrmysqltest3/slave1/conf.d:/etc/mysql/conf.d \ 26 -e MYSQL_ROOT_PASSWORD=lhr \ 27 mysql:5.7.36 28 29-- 申请从库2环境 30docker run -d --name MSS57S33652 \ 31 -h slave2 -p 33652:3306 --net=mysqln0 --ip 172.72.0.52 \ 32 -v /lhrmysqltest3/slave2/conf.d:/etc/mysql/conf.d \ 33 -e MYSQL_ROOT_PASSWORD=lhr \ 34 mysql:5.7.36 35 36 37-- 配置主库参数 38cat > /lhrmysqltest3/master/conf.d/my.cnf <<"EOF" 39[mysqld] 40port=3306 41character_set_server=utf8mb4 42secure_file_priv= 43server-id = 5733650 44log-bin = 45binlog_format=row 46skip-name-resolve 47gtid-mode=ON 48enforce-gtid-consistency=on 49report_host=172.72.0.50 50default-time-zone = '+8:00' 51log_timestamps = SYSTEM 52log_slave_updates = 1 53master_info_repository='table' 54relay_log_info_repository='table' 55relay_log_recovery=1 56 57EOF 58 59-- 配置从库1参数 60cat > /lhrmysqltest3/slave1/conf.d/my.cnf <<"EOF" 61[mysqld] 62port=3306 63character_set_server=utf8mb4 64secure_file_priv= 65server-id = 5733651 66log-bin = 67binlog_format=row 68gtid-mode=ON 69enforce-gtid-consistency=ON 70skip_name_resolve 71report_host=172.72.0.51 72default-time-zone = '+8:00' 73log_timestamps = SYSTEM 74log_slave_updates = 1 75master_info_repository='table' 76relay_log_info_repository='table' 77relay_log_recovery=1 78 79EOF 80 81 82-- 配置从库2参数 83cat > /lhrmysqltest3/slave2/conf.d/my.cnf <<"EOF" 84[mysqld] 85user=mysql 86port=3306 87character_set_server=utf8mb4 88secure_file_priv= 89server-id = 5733652 90log-bin = 91binlog_format=row 92gtid-mode=ON 93enforce-gtid-consistency=ON 94skip_name_resolve 95report_host=172.72.0.52 96default-time-zone = '+8:00' 97log_timestamps = SYSTEM 98log_slave_updates = 1 99master_info_repository='table'100relay_log_info_repository='table'101relay_log_recovery=1102103EOF104105-- 重启3台环境106docker restart MSS57M33650 MSS57S33651 MSS57S33652107docker ps108109[root@docker35 ~]# docker ps110CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES111b6311aac4c08 mysql:5.7.36 "docker-entrypoint.s…" 6 seconds ago Up 3 seconds 33060/tcp, 0.0.0.0:33652->3306/tcp, :::33652->3306/tcp MSS57S33652112b1f5f35c4fea mysql:5.7.36 "docker-entrypoint.s…" 11 seconds ago Up 8 seconds 33060/tcp, 0.0.0.0:33651->3306/tcp, :::33651->3306/tcp MSS57S336511139a9826423f2d mysql:5.7.36 "docker-entrypoint.s…" 17 seconds ago Up 15 seconds 33060/tcp, 0.0.0.0:33650->3306/tcp, :::33650->3306/tcp MSS57M33650114115-- 登陆116docker exec -it MSS57M33650 bash117docker exec -it MSS57M33650 mysql -uroot -plhr118119-- 查询120mysql -uroot -plhr -h192.168.88.35 -P33650 -e "select @@hostname,@@server_id,@@server_uuid"121mysql -uroot -plhr -h192.168.88.35 -P33651 -e "select @@hostname,@@server_id,@@server_uuid"122mysql -uroot -plhr -h192.168.88.35 -P33652 -e "select @@hostname,@@server_id,@@server_uuid"123124C:\Users\lhrxxt>mysql -uroot -plhr -h192.168.88.35 -P33650 -e "select @@hostname,@@server_id,@@server_uuid"125mysql: [Warning] Using a password on the command line interface can be insecure.126+------------+-------------+--------------------------------------+127| @@hostname | @@server_id | @@server_uuid |128+------------+-------------+--------------------------------------+129| master | 5733650 | a5c6a094-dbf1-11ec-8f03-0242ac480032 |130+------------+-------------+--------------------------------------+131132C:\Users\lhrxxt>mysql -uroot -plhr -h192.168.88.35 -P33651 -e "select @@hostname,@@server_id,@@server_uuid"133mysql: [Warning] Using a password on the command line interface can be insecure.134+------------+-------------+--------------------------------------+135| @@hostname | @@server_id | @@server_uuid |136+------------+-------------+--------------------------------------+137| slave1 | 5733651 | a99e5d38-dbf1-11ec-bfe9-0242ac480033 |138+------------+-------------+--------------------------------------+139140C:\Users\lhrxxt>mysql -uroot -plhr -h192.168.88.35 -P33652 -e "select @@hostname,@@server_id,@@server_uuid"141mysql: [Warning] Using a password on the command line interface can be insecure.142+------------+-------------+--------------------------------------+143| @@hostname | @@server_id | @@server_uuid |144+------------+-------------+--------------------------------------+145| slave2 | 5733652 | ac918575-dbf1-11ec-b236-0242ac480034 |146+------------+-------------+--------------------------------------+2、主库配置
1-- 主库创建复制用户repl 2mysql -uroot -plhr -h192.168.88.35 -P33650 3grant replication slave on *.* to repl@'%' identified by 'lhr'; 4select user,host,grant_priv,password_last_changed,authentication_string from mysql.user; 5 6create database lhrdb; 7use lhrdb; 8create table mytb1(id int,name varchar(30)); 9insert into mytb1 values(1,'a'),(2,'b');101112-- 安装插件13INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';14INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';15SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE '%semi%';1617-- 配置参数，后期需要配置到参数文件中去18set global rpl_semi_sync_master_enabled=on;1920-- 查询21show master status ;22show slave hosts;23select @@hostname,@@server_id,@@server_uuid;执行过程：
1MySQL [lhrdb]> show master status ; 2+-------------------+----------+--------------+------------------+------------------------------------------+ 3| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set | 4+-------------------+----------+--------------+------------------+------------------------------------------+ 5| master-bin.000004 | 1085 | | | 1bc15639-bc5b-11eb-b1eb-0242ac480032:1-9 | 6+-------------------+----------+--------------+------------------+------------------------------------------+ 71 row in set (0.06 sec) 8 9MySQL [lhrdb]> show slave hosts;10Empty set (0.06 sec)1112MySQL [lhrdb]> select @@hostname,@@server_id,@@server_uuid;13+------------+-------------+--------------------------------------+14| @@hostname | @@server_id | @@server_uuid |15+------------+-------------+--------------------------------------+16| master | 5733650 | 1bc15639-bc5b-11eb-b1eb-0242ac480032 |17+------------+-------------+--------------------------------------+181 row in set (0.05 sec)192021MySQL [lhrdb]> INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';22Query OK, 0 rows affected (0.08 sec)2324MySQL [(none)]> INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';25Query OK, 0 rows affected (0.08 sec)2627MySQL [lhrdb]> SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE '%semi%';28+----------------------+---------------+29| PLUGIN_NAME | PLUGIN_STATUS |30+----------------------+---------------+31| rpl_semi_sync_master | ACTIVE |32| rpl_semi_sync_slave | ACTIVE |33+----------------------+---------------+342 rows in set (0.00 sec)3536MySQL [lhrdb]> set global rpl_semi_sync_master_enabled=on;37Query OK, 0 rows affected (0.05 sec)3839MySQL [lhrdb]> show variables like '%semi%';40+-------------------------------------------+------------+41| Variable_name | Value |42+-------------------------------------------+------------+43| rpl_semi_sync_master_enabled | ON |44| rpl_semi_sync_master_timeout | 10000 |45| rpl_semi_sync_master_trace_level | 32 |46| rpl_semi_sync_master_wait_for_slave_count | 1 |47| rpl_semi_sync_master_wait_no_slave | ON |48| rpl_semi_sync_master_wait_point | AFTER_SYNC |49| rpl_semi_sync_slave_enabled | OFF |50| rpl_semi_sync_slave_trace_level | 32 |51+-------------------------------------------+------------+528 rows in set (0.01 sec)3、从库1配置
1-- 从库1 2mysql -uroot -plhr -h192.168.88.35 -P33651 3 4-- 安装插件 5INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so'; 6INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so'; 7SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE '%semi%'; 8 910-- 配置参数，后期需要配置到参数文件中去11set global rpl_semi_sync_slave_enabled=on;121314-- 修改参数15change master to16master_host='172.72.0.50',17master_port=3306,18master_user='repl',19master_password='lhr',20master_auto_position=1;2122-- 启动复制进程23start slave; 24show slave status \G;2526SELECT * FROM lhrdb.mytb1;2728-- 主库：29insert into mytb1 values(3,'c'),(4,'d');4、从库2配置
1-- S2 2mysql -uroot -plhr -h192.168.88.35 -P33652 3 4 5 6-- 安装插件 7INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so'; 8INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so'; 9SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME LIKE '%semi%';1011-- 配置参数，后期需要配置到参数文件中去12set global rpl_semi_sync_slave_enabled=on;131415-- 修改参数16change master to master_host='172.72.0.50',17master_port=3306,18master_user='repl',19master_password='lhr',20master_auto_position=1;2122start slave; 23show slave status \G;2425SELECT * FROM lhrdb.mytb1;5、主从查询
1-- 主库 2show slave hosts; 3show master status; 4show global status like 'rpl_semi%'; 5show variables like '%Rpl%'; 6 7-- 从库 8show slave status; 9show variables like '%Rpl%';10111213-- 线程查询14SELECT *15FROM performance_schema.threads a16WHERE a.`NAME` IN ( 'thread/sql/slave_IO', 'thread/sql/slave_sql' ) or a.PROCESSLIST_COMMAND in ('Binlog Dump','Binlog Dump GTID') ;1718SELECT * FROM information_schema.`PROCESSLIST` a where a.USER='system user' or a.command in ('Binlog Dump','Binlog Dump GTID') ;半同步复制查询：
1-- 主库 2MySQL [lhrdb]> show global status like 'rpl_semi%'; 3+--------------------------------------------+-------+ 4| Variable_name | Value | 5+--------------------------------------------+-------+ 6| Rpl_semi_sync_master_clients | 2 | 7| Rpl_semi_sync_master_net_avg_wait_time | 0 | 8| Rpl_semi_sync_master_net_wait_time | 0 | 9| Rpl_semi_sync_master_net_waits | 1 |10| Rpl_semi_sync_master_no_times | 0 |11| Rpl_semi_sync_master_no_tx | 0 |12| Rpl_semi_sync_master_status | ON |13| Rpl_semi_sync_master_timefunc_failures | 0 |14| Rpl_semi_sync_master_tx_avg_wait_time | 747 |15| Rpl_semi_sync_master_tx_wait_time | 747 |16| Rpl_semi_sync_master_tx_waits | 1 |17| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |18| Rpl_semi_sync_master_wait_sessions | 0 |19| Rpl_semi_sync_master_yes_tx | 1 |20| Rpl_semi_sync_slave_status | OFF |21+--------------------------------------------+-------+2215 rows in set (0.01 sec)2324MySQL [lhrdb]> show variables like '%Rpl%';25+-------------------------------------------+------------+26| Variable_name | Value |27+-------------------------------------------+------------+28| rpl_semi_sync_master_enabled | ON |29| rpl_semi_sync_master_timeout | 10000 |30| rpl_semi_sync_master_trace_level | 32 |31| rpl_semi_sync_master_wait_for_slave_count | 1 |32| rpl_semi_sync_master_wait_no_slave | ON |33| rpl_semi_sync_master_wait_point | AFTER_SYNC |34| rpl_semi_sync_slave_enabled | OFF |35| rpl_semi_sync_slave_trace_level | 32 |36| rpl_stop_slave_timeout | 31536000 |37+-------------------------------------------+------------+389 rows in set (0.09 sec)3940-- 从库41MySQL [(none)]> show global status like 'Rpl_semi_sync_slave_status%';42+----------------------------+-------+43| Variable_name | Value |44+----------------------------+-------+45| Rpl_semi_sync_slave_status | ON |46+----------------------------+-------+471 row in set (0.05 sec)Rpl_semi_sync_master_clients表示记录支持半同步的slave的个数
Rpl_semi_sync_master_status标记master现在是否是半同步复制状态
6、测试半同步复制
测试过程：
1、关闭从库io线程，模拟网络卡顿
2、主库插入数据，等待10秒，同步方式自动转换为异步模式
3、从库启动io线程
4、同步方式变为半同步模式
先关闭一个从库，我们测试1主1从的情况。
二、配置延迟复制示例
我们把从库2配置为延迟从库，如下所示：
1STOP SLAVE SQL_THREAD; 2CHANGE MASTER TO MASTER_DELAY = 120; 3START SLAVE SQL_THREAD; 4 5show slave status \G 6返回：SQL_Delay: 120 7 8 9-- 主库插入数据10insert into mytb1 values(5,'e'),(6,'f');11select * from mytb1;1213-- 从库2查询14show slave status \G1516Seconds_Behind_Master: 11017SQL_Remaining_Delay: 4618Slave_SQL_Running_State: Waiting until MASTER_DELAY seconds after master executed event三、配置并行复制示例
3.1、主库配置
1set global binlog_group_commit_sync_delay=10;2set global binlog_group_commit_sync_no_delay_count=10;3show variables like 'binlog_group_commit_sync_%';3.2、从库2配置并行复制
只在从库2做配置，从库1不做配置。
1STOP SLAVE SQL_THREAD; 2set global slave_parallel_type=LOGICAL_CLOCK; 3set global slave_parallel_workers=4; 4 5show variables like 'slave_parallel%'; 6 7start SLAVE SQL_THREAD; 8 9-- 线程查询10SELECT *11FROM performance_schema.threads a12WHERE a.`NAME` IN ( 'thread/sql/slave_IO', 'thread/sql/slave_sql','thread/sql/slave_worker' ) or a.PROCESSLIST_COMMAND in ('Binlog Dump','Binlog Dump GTID') ;1314SELECT * FROM information_schema.`PROCESSLIST` a where a.USER='system user' or a.command in ('Binlog Dump','Binlog Dump GTID') ;151617MySQL [(none)]> SELECT *18 -> FROM performance_schema.threads a19 -> WHERE a.`NAME` IN ( 'thread/sql/slave_IO', 'thread/sql/slave_sql','thread/sql/slave_worker' ) or a.PROCESSLIST_COMMAND in ('Binlog Dump','Binlog Dump GTID') ;20+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+21| THREAD_ID | NAME | TYPE | PROCESSLIST_ID | PROCESSLIST_USER | PROCESSLIST_HOST | PROCESSLIST_DB | PROCESSLIST_COMMAND | PROCESSLIST_TIME | PROCESSLIST_STATE | PROCESSLIST_INFO | PARENT_THREAD_ID | ROLE | INSTRUMENTED | HISTORY | CONNECTION_TYPE | THREAD_OS_ID |22+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+23| 33 | thread/sql/slave_io | FOREGROUND | 8 | root | 172.72.0.1 | NULL | Connect | 1203 | Waiting for master to send event | NULL | 30 | NULL | YES | YES | NULL | 79 |24| 36 | thread/sql/slave_sql | FOREGROUND | 11 | root | 172.72.0.1 | NULL | Connect | 312 | Slave has read all relay log; waiting for more updates | NULL | 30 | NULL | YES | YES | NULL | 82 |25| 37 | thread/sql/slave_worker | FOREGROUND | 12 | root | 172.72.0.1 | NULL | Connect | 312 | Waiting for an event from Coordinator | NULL | 36 | NULL | YES | YES | NULL | 83 |26| 38 | thread/sql/slave_worker | FOREGROUND | 13 | root | 172.72.0.1 | NULL | Connect | 312 | Waiting for an event from Coordinator | NULL | 36 | NULL | YES | YES | NULL | 84 |27| 39 | thread/sql/slave_worker | FOREGROUND | 14 | root | 172.72.0.1 | NULL | Connect | 312 | Waiting for an event from Coordinator | NULL | 36 | NULL | YES | YES | NULL | 85 |28| 40 | thread/sql/slave_worker | FOREGROUND | 15 | root | 172.72.0.1 | NULL | Connect | 312 | Waiting for an event from Coordinator | NULL | 36 | NULL | YES | YES | NULL | 86 |29+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+306 rows in set (0.05 sec)3132MySQL [(none)]> SELECT * FROM information_schema.`PROCESSLIST` a where a.USER='system user' or a.command in ('Binlog Dump','Binlog Dump GTID') ;33+----+-------------+------+------+---------+------+--------------------------------------------------------+------+34| ID | USER | HOST | DB | COMMAND | TIME | STATE | INFO |35+----+-------------+------+------+---------+------+--------------------------------------------------------+------+36| 14 | system user | | NULL | Connect | 37 | Waiting for an event from Coordinator | NULL |37| 15 | system user | | NULL | Connect | 37 | Waiting for an event from Coordinator | NULL |38| 12 | system user | | NULL | Connect | 37 | Waiting for an event from Coordinator | NULL |39| 13 | system user | | NULL | Connect | 37 | Waiting for an event from Coordinator | NULL |40| 11 | system user | | NULL | Connect | 37 | Slave has read all relay log; waiting for more updates | NULL |41| 8 | system user | | NULL | Connect | 928 | Waiting for master to send event | NULL |42+----+-------------+------+------+---------+------+--------------------------------------------------------+------+436 rows in set (0.05 sec)3.3、主库压测测试并行复制
因为这里的架构为1主2从，我只配置了从库2为并行复制，从库1不是并行复制，那么接下来测试并行复制的效果。
首先，取消从库2的延迟复制功能：
1STOP SLAVE SQL_THREAD;2CHANGE MASTER TO MASTER_DELAY = 0;3START SLAVE SQL_THREAD;45show slave status \G6返回：SQL_Delay: 0首先，主库进行压测生成数据：
1-- 主库修改 2set GLOBAL max_connections=10000; 3set global max_prepared_stmt_count=65536; 4 5-- 做压测 6sysbench /usr/share/sysbench/oltp_common.lua --time=300 --mysql-host=172.72.0.50 --mysql-port=3306 \ 7--mysql-user=root --mysql-password=lhr --mysql-db=lhrdb --table-size=100000 --tables=10 \ 8--threads=16 --events=999999999 prepare 91011sysbench /usr/share/sysbench/oltp_read_write.lua --time=300 --mysql-host=172.72.0.50 --mysql-port=3306 \12--mysql-user=root --mysql-password=lhr --mysql-db=lhrdb --table-size=1000000 --tables=10 --threads=16 \13--events=999999999 --report-interval=10 --db-ps-mode=disable --forced-shutdown=1 run14151617-- 查询从库18mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master19mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master20结果：
1[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master 2mysql: [Warning] Using a password on the command line interface can be insecure. 3 Seconds_Behind_Master: 126 4[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master 5mysql: [Warning] Using a password on the command line interface can be insecure. 6 Seconds_Behind_Master: 62 7[root@docker35 ~]# 8[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master 9mysql: [Warning] Using a password on the command line interface can be insecure.10 Seconds_Behind_Master: 13911[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master12mysql: [Warning] Using a password on the command line interface can be insecure.13 Seconds_Behind_Master: 6514[root@docker35 ~]# 15[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master16mysql: [Warning] Using a password on the command line interface can be insecure.17 Seconds_Behind_Master: 21418[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master19mysql: [Warning] Using a password on the command line interface can be insecure.20 Seconds_Behind_Master: 78可以看到，从库2比从库1能至少快一倍。
若是将从库的slave_parallel_workers配置为16，则配置了并行复制的库基本无延迟，而没有配置并行复制的库，延迟会越来越严重：
1STOP SLAVE SQL_THREAD; 2set global slave_parallel_workers=16; 3 4show variables like 'slave_parallel%'; 5 6start SLAVE SQL_THREAD; 7 8-- 线程查询 9SELECT *10FROM performance_schema.threads a11WHERE a.`NAME` IN ( 'thread/sql/slave_IO', 'thread/sql/slave_sql','thread/sql/slave_worker' ) or a.PROCESSLIST_COMMAND in ('Binlog Dump','Binlog Dump GTID') ;1213SELECT * FROM information_schema.`PROCESSLIST` a where a.USER='system user' or a.command in ('Binlog Dump','Binlog Dump GTID') ;141516MySQL [lhrdb]> -- 线程查询17MySQL [lhrdb]> SELECT *18 -> FROM performance_schema.threads a19 -> WHERE a.`NAME` IN ( 'thread/sql/slave_IO', 'thread/sql/slave_sql','thread/sql/slave_worker' ) or a.PROCESSLIST_COMMAND in ('Binlog Dump','Binlog Dump GTID') ;20+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+21| THREAD_ID | NAME | TYPE | PROCESSLIST_ID | PROCESSLIST_USER | PROCESSLIST_HOST | PROCESSLIST_DB | PROCESSLIST_COMMAND | PROCESSLIST_TIME | PROCESSLIST_STATE | PROCESSLIST_INFO | PARENT_THREAD_ID | ROLE | INSTRUMENTED | HISTORY | CONNECTION_TYPE | THREAD_OS_ID |22+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+23| 29 | thread/sql/slave_io | FOREGROUND | 4 | root | 192.168.88.64 | NULL | Connect | 1780 | Waiting for master to send event | NULL | 28 | NULL | YES | YES | NULL | 154 |24| 106 | thread/sql/slave_sql | FOREGROUND | 81 | root | 192.168.88.64 | NULL | Connect | 24 | Slave has read all relay log; waiting for more updates | NULL | 28 | NULL | YES | YES | NULL | 168 |25| 107 | thread/sql/slave_worker | FOREGROUND | 82 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 169 |26| 108 | thread/sql/slave_worker | FOREGROUND | 83 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 170 |27| 109 | thread/sql/slave_worker | FOREGROUND | 84 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 171 |28| 110 | thread/sql/slave_worker | FOREGROUND | 85 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 172 |29| 111 | thread/sql/slave_worker | FOREGROUND | 86 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 173 |30| 112 | thread/sql/slave_worker | FOREGROUND | 87 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 174 |31| 113 | thread/sql/slave_worker | FOREGROUND | 88 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 175 |32| 114 | thread/sql/slave_worker | FOREGROUND | 89 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 176 |33| 115 | thread/sql/slave_worker | FOREGROUND | 90 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 177 |34| 116 | thread/sql/slave_worker | FOREGROUND | 91 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 178 |35| 117 | thread/sql/slave_worker | FOREGROUND | 92 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 179 |36| 118 | thread/sql/slave_worker | FOREGROUND | 93 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 180 |37| 119 | thread/sql/slave_worker | FOREGROUND | 94 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 181 |38| 120 | thread/sql/slave_worker | FOREGROUND | 95 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 182 |39| 121 | thread/sql/slave_worker | FOREGROUND | 96 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 183 |40| 122 | thread/sql/slave_worker | FOREGROUND | 97 | root | 192.168.88.64 | NULL | Connect | 322 | Waiting for an event from Coordinator | BEGIN | 106 | NULL | YES | YES | NULL | 184 |41+-----------+-------------------------+------------+----------------+------------------+------------------+----------------+---------------------+------------------+--------------------------------------------------------+------------------+------------------+------+--------------+---------+-----------------+--------------+4218 rows in set (0.01 sec)4344MySQL [lhrdb]>45MySQL [lhrdb]> SELECT * FROM information_schema.`PROCESSLIST` a where a.USER='system user' or a.command in ('Binlog Dump','Binlog Dump GTID') ;46+----+-------------+------+------+---------+------+--------------------------------------------------------+------+47| ID | USER | HOST | DB | COMMAND | TIME | STATE | INFO |48+----+-------------+------+------+---------+------+--------------------------------------------------------+------+49| 96 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |50| 97 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |51| 94 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |52| 95 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |53| 92 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |54| 93 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |55| 90 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |56| 91 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |57| 88 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |58| 89 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |59| 86 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |60| 87 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |61| 84 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |62| 82 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |63| 85 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |64| 83 | system user | | NULL | Connect | 322 | Waiting for an event from Coordinator | NULL |65| 81 | system user | | NULL | Connect | 24 | Slave has read all relay log; waiting for more updates | NULL |66| 4 | system user | | NULL | Connect | 1780 | Waiting for master to send event | NULL |67+----+-------------+------+------+---------+------+--------------------------------------------------------+------+6818 rows in set (0.01 sec)重新测试，可以看到从库2基本无延迟了：
1[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master 2mysql: [Warning] Using a password on the command line interface can be insecure. 3 Seconds_Behind_Master: 50 4[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master 5mysql: [Warning] Using a password on the command line interface can be insecure. 6 Seconds_Behind_Master: 0 7[root@docker35 ~]# 8[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master 9mysql: [Warning] Using a password on the command line interface can be insecure.10mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master11 Seconds_Behind_Master: 13112[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master13mysql: [Warning] Using a password on the command line interface can be insecure.14 Seconds_Behind_Master: 11516[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master17mysql: [Warning] Using a password on the command line interface can be insecure.18 Seconds_Behind_Master: 21019[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master20mysql: [Warning] Using a password on the command line interface can be insecure.21 Seconds_Behind_Master: 122[root@docker35 ~]# 23[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33651 -e "show slave status \G" | grep Seconds_Behind_Master24mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Mastermysql: [Warning] Using a password on the command line interface can be insecure.25 Seconds_Behind_Master: 38126[root@docker35 ~]# mysql -uroot -plhr -h192.168.88.35 -P33652 -e "show slave status \G" | grep Seconds_Behind_Master27mysql: [Warning] Using a password on the command line interface can be insecure.28 Seconds_Behind_Master: 1 29