实验目的：
体验在数据库中配置多个slave线程进行同放操作有助于提高复制效率，减少主从数据库的数据差异。
操作演示：
在my.conf文件中加入
slave_parallel_threads=N，N为并行数量。
[root@dbserver2 bin]#
cat /etc/my.cnf
#
# This group is read both both by the client and the server
# use it for options that affect everything
#
[client-server]
#
# include all files from the config directory
#
!includedir /etc/my.cnf.d
[mysqld]
log-bin=logbin
server_id=2
expire_logs_days=7
slave_parallel_threads=2
MariaDB [(none)]>
show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.221.135
Master_User: slave_user
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: logbin.000034
Read_Master_Log_Pos: 323
Relay_Log_File: dbserver2-relay-bin.000002
Relay_Log_Pos: 607
Relay_Master_Log_File: logbin.000034
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 323
Relay_Log_Space: 908
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_SSL_Crl:
Master_SSL_Crlpath:
Using_Gtid: Slave_Pos
Gtid_IO_Pos: 0-1-12
1 row in set (0.00 sec)
可以看到已经有2个并行的进程在等待了：
MariaDB [(none)]>
show processlist;
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
| 3 | system user | | NULL | Connect | 148 | Waiting for work from SQL thread | NULL | 0.000 |
| 4 | system user | | NULL | Connect | 148 | Waiting for work from SQL thread | NULL | 0.000 |
| 5 | system user | | NULL | Connect | 148 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL | 0.000 |
| 6 | system user | | NULL | Connect | 148 | Waiting for master to send event | NULL | 0.000 |
| 8 | root | localhost | NULL | Query | 0 | init | show processlist | 0.000 |
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
5 rows in set (0.00 sec)
提升到5的并发，看一下是否有5个线程在等待：
[root@dbserver2 bin]#
cat /etc/my.cnf
#
# This group is read both both by the client and the server
# use it for options that affect everything
#
[client-server]
#
# include all files from the config directory
#
!includedir /etc/my.cnf.d
[mysqld]
log-bin=logbin
server_id=2
expire_logs_days=7
slave_parallel_threads=5
验证是否分配了5个并发：
MariaDB [(none)]>
start slave;
Query OK, 0 rows affected, 1 warning (0.00 sec)
MariaDB [(none)]>
show processlist;
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
| 3 | system user | | NULL | Connect | 14 | Waiting for work from SQL thread | NULL | 0.000 |
| 4 | system user | | NULL | Connect | 14 | Waiting for work from SQL thread | NULL | 0.000 |
| 5 | system user | | NULL | Connect | 14 | Waiting for work from SQL thread | NULL | 0.000 |
| 6 | system user | | NULL | Connect | 14 | Waiting for work from SQL thread | NULL | 0.000 |
| 7 | system user | | NULL | Connect | 14 | Waiting for work from SQL thread | NULL | 0.000 |
| 8 | system user | | NULL | Connect | 14 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL | 0.000 |
| 9 | system user | | NULL | Connect | 14 | Waiting for master to send event | NULL | 0.000 |
| 11 | root | localhost | NULL | Query | 0 | init | show processlist | 0.000 |
+----+-------------+-----------+------+---------+------+-----------------------------------------------------------------------------+------------------+----------+
8 rows in set (0.00 sec)
MariaDB [(none)]>
show processlist\G;
*************************** 1. row ***************************
Id: 3
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for work from SQL thread
Info: NULL
Progress: 0.000
*************************** 2. row ***************************
Id: 4
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for work from SQL thread
Info: NULL
Progress: 0.000
*************************** 3. row ***************************
Id: 5
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for work from SQL thread
Info: NULL
Progress: 0.000
*************************** 4. row ***************************
Id: 6
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for work from SQL thread
Info: NULL
Progress: 0.000
*************************** 5. row ***************************
Id: 7
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for work from SQL thread
Info: NULL
Progress: 0.000
*************************** 6. row ***************************
Id: 8
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Slave has read all relay log; waiting for the slave I/O thread to update it
Info: NULL
Progress: 0.000
*************************** 7. row ***************************
Id: 9
User: system user
Host:
db: NULL
Command: Connect
Time: 36
State: Waiting for master to send event
Info: NULL
Progress: 0.000
*************************** 8. row ***************************
Id: 11
User: root
Host: localhost
db: NULL
Command: Query
Time: 0
State: init
Info: show processlist
Progress: 0.000
8 rows in set (0.00 sec)
OK,已经有5个线程在等待重放主库的binlog！~~~
