本篇文章为大家展示了MySQL5.5中怎么实现半同步复制，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

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master:192.168.70.101

slave:192.168.70.100

在master上创建用户repl(只需要在master上创建repl用户);

mysql>grant replication slave on *.* to 'repl'@'192.168.70.100' identified by 'repl';

在master上my.cnf配置如下：

[mysqld]
datadir=/data/dbdata
user=mysql
port=3306
innodb_data_home_dir = /data/dbdata
socket          = /usr/local/mysql/tmp/mysql.sock
server-id=2
log-bin=master-bin
log-bin-index=master-bin.index
sync_binlog = 1
binlog_format = row
character-set-server=utf8

在slave的my.cnf中配置如下：

[mysqld]
innodb_data_home_dir = /data/dbdata
socket = /usr/local/mysql/tmp/mysql.sockport=3306
user=mysql
default-storage-engine=innodb
server-id=3
read_only=on
log-bin=slave-bin
relay_log=slave-relay-bin
relay-log-index=slave-relay-bin.index
binlog_format = row
default-storage-engine=InnoDB
character-set-server=utf8

在master上产看，

mysql> show master status;
+-------------------+----------+--------------+------------------+
| File              | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+-------------------+----------+--------------+------------------+
| master-bin.000003 |      106 |              |                  |
+-------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

在slave上使用change master to命令将slave指向master。然后使用start slave命令启动复制。

 mysql> change master to 　　　　

->master_host='192.168.70.101',

->master_port=3306,

->master_user='repl',

->master_password='repl',

->master_log_file='master-bin.000003',

->master_log_pos=106;

mysql> start slave;
Query OK, 0 rows affected (0.00 sec)

mysql> show slave status\G;
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.70.101
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: master-bin.000003
          Read_Master_Log_Pos: 106
               Relay_Log_File: slave-relay-bin.000003
                Relay_Log_Pos: 252
        Relay_Master_Log_File: master-bin.000003
             Slave_IO_Running: Yes   　　---成功
            Slave_SQL_Running: Yes 　　 ---成功

flush logs命令强制轮换二进制日志，从而可以得到完整的二进制日志文件。

使用show binlog events in 'master-bin.000004(二进制日志)'\G;

检查二进制日志里有哪些事件

mysql> show binlog events in 'master-bin.000004'\G;
*************************** 1. row ***************************
   Log_name: master-bin.000004
        Pos: 4
 Event_type: Format_desc
  Server_id: 2
End_log_pos: 106
       Info: Server ver: 5.1.56-community-log, Binlog ver: 4
*************************** 2. row ***************************
   Log_name: master-bin.000004
        Pos: 106
 Event_type: Query
  Server_id: 2
End_log_pos: 200
       Info: use `test`; create table tb1(text char(10))
*************************** 3. row ***************************
   Log_name: master-bin.000004
        Pos: 200
 Event_type: Rotate
  Server_id: 2
End_log_pos: 244
       Info: master-bin.000005;pos=4
3 rows in set (0.00 sec)

//克隆MASTER

[root@server picture]# mysqldump -uroot -pmysql --host=192.168.70.101 --all-databases --master-data=1 > backup-source.sql

--master-data=1选项mysqldump写change master to 语句，且参数为二进制日志文件及其位置。

然后在slave上恢复备份：

[root@server picture]#mysql -uroot -pmysql --host=192.168.70.100 < backup-source.sql

//克隆SLAVE

//清除Binlog日志

服务器自动清理旧的binlog文件，需设置expire-logs-days选项，这个选项可以作为服务器变量。如果服务重启后，不受影响，需要在my.cnf设置。

使用purge binary log命令手工清除binlog文件。格式如下：

1，purge binary log before datatime

将清除在给定时间之前的所有文件。

2,purge binary logs to 'filename'

将清除在给定文件之前的所有文件。

//默认情况下，由slave执行的事件没有被记录到二进制日志中，如果这个slave是master的一个备份，这时会出现问题。

在my.cnf添加log-slave-updates，以确保来自于master并被执行的语句会被写入slave的二进制日志中。

切换基本思路：为了让slave赶上备份服务器，并在正确的位置停止，使用start slave until命令。

slave>start slave until master_log_file='master-bin-000006',master_log_pos=700;

slave>select master_pos_wait('master-bin-000006',700);

//在主从服务器上配置支持半同步复制

[MASTER]
mysql>install plugin rpl_semi_sync_master soname ‘semisync_master.so’;

mysql> SELECT * FROM information_schema.PLUGINS WHERE PLUGIN_NAME='rpl_semi_sync_master'\G;
*************************** 1. row ***************************
           PLUGIN_NAME: rpl_semi_sync_master
        PLUGIN_VERSION: 1.0
         PLUGIN_STATUS: ACTIVE
           PLUGIN_TYPE: REPLICATION
   PLUGIN_TYPE_VERSION: 1.0
        PLUGIN_LIBRARY: semisync_master.so
PLUGIN_LIBRARY_VERSION: 1.3
         PLUGIN_AUTHOR: He Zhenxing
    PLUGIN_DESCRIPTION: Semi-synchronous replication master
        PLUGIN_LICENSE: GPL
           LOAD_OPTION: ON
1 row in set (0.00 sec)

mysql> show variables like 'rpl_semi_sync%';
+------------------------------------+-------+
| Variable_name                      | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled       | OFF   |
| rpl_semi_sync_master_timeout       | 10000 |
| rpl_semi_sync_master_trace_level   | 32    |
| rpl_semi_sync_master_wait_no_slave | ON    |
+------------------------------------+-------+

修改rpl_semi_sync_master_enabled=ON,rpl_semi_sync_master_timeout单位时间为毫秒。

mysql> set global rpl_semi_sync_master_enabled = on;    
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like 'rpl_semi_sync%';
+------------------------------------+-------+
| Variable_name                      | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled       | ON    |
| rpl_semi_sync_master_timeout       | 10000 |
| rpl_semi_sync_master_trace_level   | 32    |
| rpl_semi_sync_master_wait_no_slave | ON    |
+------------------------------------+-------+
4 rows in set (0.00 sec)

mysql> show global status like 'Rpl_semi_sync%';
+--------------------------------------------+-------+
| Variable_name                              | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients               | 0     |
| Rpl_semi_sync_master_net_avg_wait_time     | 0     |
| Rpl_semi_sync_master_net_wait_time         | 0     |
| Rpl_semi_sync_master_net_waits             | 0     |
| Rpl_semi_sync_master_no_times              | 0     |
| Rpl_semi_sync_master_no_tx                 | 0     |
| Rpl_semi_sync_master_status                | OFF   |
| Rpl_semi_sync_master_timefunc_failures     | 0     |
| Rpl_semi_sync_master_tx_avg_wait_time      | 0     |
| Rpl_semi_sync_master_tx_wait_time          | 0     |
| Rpl_semi_sync_master_tx_waits              | 0     |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0     |
| Rpl_semi_sync_master_wait_sessions         | 0     |
| Rpl_semi_sync_master_yes_tx                | 0     |
+--------------------------------------------+-------+
下面的变量仅仅在主服务的半复制插件初始化后才有效，参数解释如下：
Rpl_semi_sync_master_clients：表示半复制从服务器的数量。
Rpl_semi_sync_master_net_avg_wait_time：主服务器等候从服务器的平均毫秒时间。(单位为毫秒)
Rpl_semi_sync_master_net_waits：主服务器等候从服务器的总毫秒时间。(单位为毫秒)
Rpl_semi_sync_master_no_times：主服务器关闭半复制的次数。
Rpl_semi_sync_master_no_tx：从服务器提交事物后没有收到ack确认成功的次数。
Rpl_semi_sync_master_status：决定半服务器是否可以在主服务器上操作，设置为ON表示开启，OFF表示关闭，为异步模式。
Rpl_semi_sync_master_timefunc_failures:主服务器调用时间函数失败的次数，例如gettimeofday()。
Rpl_semi_sync_master_tx_avg_wait_time：主服务器等候每个事物的平均时间(毫秒)。
Rpl_semi_sync_master_tx_waits：主服务器等候事物的总次数。
Rpl_semi_sync_master_wait_pos_backtraverse：
Rpl_semi_sync_master_wait_sessions：正在等候从服务器回复的会话数。
Rpl_semi_sync_master_yes_tx：从服务器成功得到答应的提交事物次数。

[SLAVE]
mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';

Rpl_semi_sync_slave_status：
rpl_semi_sync_slave_enabled：
rpl_semi_sync_slave_trace_level：

mysql> show global variables like 'rpl_semi_sync%';
+------------------------------------+-------+
| Variable_name                      | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled       | OFF   |
| rpl_semi_sync_master_timeout       | 10000 |
| rpl_semi_sync_master_trace_level   | 32    |
| rpl_semi_sync_master_wait_no_slave | ON    |
| rpl_semi_sync_slave_enabled        | OFF   |
| rpl_semi_sync_slave_trace_level    | 32    |
+------------------------------------+-------+
6 rows in set (0.00 sec)

mysql> set global rpl_semi_sync_master_enabled = on;
Query OK, 0 rows affected (0.00 sec)

mysql> set global rpl_semi_sync_slave_enabled  = on;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like 'rpl_semi_sync%';
+------------------------------------+-------+
| Variable_name                      | Value |
+------------------------------------+-------+
| rpl_semi_sync_master_enabled       | ON    |
| rpl_semi_sync_master_timeout       | 10000 |
| rpl_semi_sync_master_trace_level   | 32    |
| rpl_semi_sync_master_wait_no_slave | ON    |
| rpl_semi_sync_slave_enabled        | ON    |
| rpl_semi_sync_slave_trace_level    | 32    |
+------------------------------------+-------+
6 rows in set (0.00 sec)

//rpl_semi_sync_master_enabled = on ：启动master 支持半同步复制
//rpl_semi_sync_slave_enabled ：启动slave支持半同步复制

当在从服务运行时调整支持半同步复制，必须重启I/O线程。
mysql> STOP SLAVE IO_THREAD; START SLAVE IO_THREAD;

在my.cnf配置文件如下：
在主服务器上:
[mysqld]
rpl_semi_sync_master_enabled=1
rpl_semi_sync_master_timeout=1000 # 1 second

在每个从服务器上:
[mysqld]
rpl_semi_sync_slave_enabled=1

//关于mysql5.5存储引擎后台打印
mysql> show engine innodb status\G;
*************************** 1. row ***************************
  Type: InnoDB
  Name:
Status:
=====================================
120330 14:37:49 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 3 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 367 1_second, 367 sleeps, 35 10_second, 19 background, 19 flush
srv_master_thread log flush and writes: 367
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 32, signal count 32
Mutex spin waits 14, rounds 420, OS waits 0
RW-shared spins 32, rounds 960, OS waits 32
RW-excl spins 0, rounds 0, OS waits 0
Spin rounds per wait: 30.00 mutex, 30.00 RW-shared, 0.00 RW-excl
------------
TRANSACTIONS
------------
Trx id counter 853
Purge done for trx's n:o < 77E undo n:o < 0
History list length 63
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started
MySQL thread id 29, OS thread handle 0x49499940, query id 5743 localhost root
show engine innodb status
--------
FILE I/O
--------
I/O thread 0 state: waiting for i/o request (insert buffer thread)
I/O thread 1 state: waiting for i/o request (log thread)
I/O thread 2 state: waiting for i/o request (read thread)
I/O thread 3 state: waiting for i/o request (read thread)
I/O thread 4 state: waiting for i/o request (read thread)
I/O thread 5 state: waiting for i/o request (read thread)
I/O thread 6 state: waiting for i/o request (write thread)
I/O thread 7 state: waiting for i/o request (write thread)
I/O thread 8 state: waiting for i/o request (write thread)
I/O thread 9 state: waiting for i/o request (write thread)
Pending normal aio reads: 0 [0, 0, 0, 0] , aio writes: 0 [0, 0, 0, 0] ,
 ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0
Pending flushes (fsync) log: 0; buffer pool: 0
379 OS file reads, 816 OS file writes, 358 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s
-------------------------------------
INSERT BUFFER AND ADAPTIVE HASH INDEX
-------------------------------------
Ibuf: size 1, free list len 0, seg size 2, 0 merges
merged operations:
 insert 0, delete mark 0, delete 0
discarded operations:
 insert 0, delete mark 0, delete 0
Hash table size 276671, node heap has 2 buffer(s)
0.00 hash searches/s, 0.00 non-hash searches/s
---
LOG
---
Log sequence number 3292715
Log flushed up to   3292715
Last checkpoint at  3292715
0 pending log writes, 0 pending chkp writes
313 log i/o's done, 0.00 log i/o's/second
----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 137363456; in additional pool allocated 0
Dictionary memory allocated 1809452
Buffer pool size   8191
Free buffers       7328
Database pages     861
Old database pages 297
Modified db pages  0
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 0, not young 0
0.00 youngs/s, 0.00 non-youngs/s
Pages read 368, created 493, written 1315
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 861, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]
--------------
ROW OPERATIONS
--------------
0 queries inside InnoDB, 0 queries in queue
1 read views open inside InnoDB
Main thread process no. 3289, id 1228495168, state: waiting for server activity
Number of rows inserted 0, updated 0, deleted 0, read 0
0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
----------------------------
END OF INNODB MONITOR OUTPUT
============================

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