This document discusses database replication in MySQL. It begins by explaining the concepts and principles of replication, including that it allows for maintaining synchronized copies of databases across multiple servers. It then covers how to set up replication between a master and slave server by enabling binary logging on the master, creating a backup, configuring the servers, restoring the backup on the slave, and starting the replication process. Finally, it discusses how to verify replication is working properly and manage the replication process ongoing.

1. Hệ quản trị cơ sở dữ liệu
Replication
Dư Phương Hạnh
Bộ môn Hệ thống thông tin
Khoa CNTT, trường Đại học Công nghệ
Đại học Quốc gia Hanoi
hanhdp@vnu.edu.vn

2. Outline




Replication concepts and principles
Setting up replication on master and slave servers
Managing replication
Replication settings
Read more at:
http://mysql-tools.com/en/replication-in-mysql.html
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3. Replication concepts and
principles
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4. Introduce
 Beside performing regular backups of your
databases, you can also replicate your databases.
 It means you maintain a copy of the database that
is kept up-to-date (synchronized) with the original
database. If the original database becomes
unavailable, the replicated database can continue
to provide users immediate access to the same
data with a minimal amount of downtime.
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5. Replicating MySQL Databases
 Updates made to one database copy are
automatically propagated to all the other replicas.
 Generally, one of the replicas is designated as
the master where Updates are directed to the
master while read queries can be addressed to
either the master or the slaves.
 If replicas other than master handle the updates,
then keeping the replicas identical becomes more
complex.
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6. Benefits of database replication
 Availability: Any replica can be used as a "hot"
backup.
– If the master database becomes unavailable, this replica
can take over and can be designated as the master. The
failures can be fixed and the failed replica can rejoin as a
slave replica.
 Backups: Replicas can be used as active backups
and can be used to perform tedious offline backups
to file systems without locking up the primary
instance.
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7. Benefits of database replication
 Load Balancing: Replicas can serve split loads, also
called load balancing, for heavily used databases.
– Read queries can be distributed to the different replicas
while updates are handled by the master. This scenario
works well when the number of read queries is far greater
than the number of update queries.
 Proximity: Some replicas can be closer to users
leading to improved response time.
 Security: It is harder for malicious users to damage
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all the replicas.
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8. Availability
One database is
the master while
the other is
designated as a
slave. Only
updates to the
master are
logged.
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9. Load Balancing
Read queries are
directed to either
the master or any
of the replicas
while update
queries are
directed only to
the master.
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10. MySQL Replication Model
MySQL replication is based on a number of principles:
1.Replication is a one-way, asynchronous process  changes
are always propagated from the master server to the slave
server, but never the other way around.
2.The primary MySQL server acts as the Master server, and
the servers that contain the copied databases are considered
the Slave servers.
3.Data always moves from the master server to the slave
server. As a result, only databases on the master server should
be updated. The updates are then propagated to the slave
servers
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11. MySQL Replication Model
4. The master server must be configured with a user account
that grants replication privileges to the slave server. The
account allows the slave server to access the master server
in order to receive updates.
5. Replication is based on the master database server
recording all updates in a binary log  binary logging must
be enabled on the master server. The logged updates are
used to synchronize the database on the slave server.
6. To avoid conflicts, update queries are directed to the master
while read queries can either go to the master or to the
slaves.
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12. MySQL Replication Model
7. The replicas connect to the master to read the
binary log and then apply the updates to catch up
with the master.
8. The slave server uses replication coordinates to
track updates.
– The coordinates are based on the name of a binary log
file on the master server and the position in that file. The
file and position represent where MySQL left off when the
last update was performed on the slave server. The
coordinates - along with other logon information - are
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stored in the master.info file on the slave host.quản trị CSDL @ BM HTTT
Hệ

13. MySQL Replication Model
9. Each server that participates in the replication process must
be assigned a unique numerical server ID. You assign the
ID by specifying the server-id option in the [mysqld] section
of the option file for each server.
10. A master server can replicate data to one or more slave
servers.
11. To set up replication, the master server and slave server
must begin with databases in a synchronized state. In other
words, the databases to be replicated must be identical
when replication is initiated.
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14. MySQL Replication Model
12. No slave server can ever have two master servers.
13. It is generally best to have the master server and
slave servers run the same version of MySQL.
14. There are two core types of replication format
– Statement Based Replication (SBR): replicates entire SQL
statements,
– Row Based Replication (RBR): replicates the changed rows
– You may also use a third variety, Mixed Based Replication
(MBR), which is the default mode within MySQL 5.1.14 and
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later.
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15. Setting up Replication
 Enable binary logging on the master server.
 Make a backup of the master database.
 Start a new binary log immediately after making the
backup.
 Set up a user account on the master server that
grants replication privileges to the slave server. The
account allows the slave server to access the
master server in order to receive updates.
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16. Setting up Replication (2)
 Assign a unique numerical server ID to each server
that participates in the replication process.
 Block all updates to the master.
 Create a Slave instance.
 Load the backup of the master database into the
slave
 Apply the updates from the binary log to the slave to
sync up with the master.
 Get both the master and slave running.
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17. Replication Files on the Slave (1)
When replication is implemented, the slave server
maintains a set of files to support the replication.
MySQL automatically creates the three types of files
on the slave server:
1.<host>-relay-bin.<extension>:Contains the
statements to be used to synchronize the replicated
database with the database on the master server, and
then it is deleted.
–
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The relay log files receive their data from the binary log
files on the master server.
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18. Replication Files on the Slave (2)
2. master.info: Contains connection information such
as the master server hostname, user account and
its password. It also maintains information about
the last binary log file on the master server to be
accessed and the position in that file.
3. relay-log.info: Contains information about the relay
log files and tracks the last position in those files in
which the replicated database was updated.
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19. Implementing Replication Details
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20. Set up Replication User (on Master)
 To allow a master server to replicate data to a slave
server, you must set up a user account on the
master server.
 The slave server then uses that account to establish
a connection to the master server
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21. Set up Replication User (on Master)
GRANT REPLICATION SLAVE ON *.* TO '<slave
account>'@'<slave host>' IDENTIFIED BY '<password>';
The REPLICATION SLAVE privilege at the global level allows
all changes to a database to be replicated to the copy of the
database on the slave server.
TO clause defines the username on the account and host from
which that account can connect. This is the host where the slave
server resides.
The IDENTIFIED BY clause then identifies the password that
should be used when the slave server logs on to the master
server.
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22. Making Initial Backup
 Make a backup of the databases that you want to replicate.
Use the --master-data option in the mysqldump command.
The --master-data option adds a CHANGE MASTER
statement similar to the following to your backup file:
CHANGE MASTER TO MASTER_LOG_FILE='mastsrvbin.000201', MASTER_LOG_POS=64;
 CHANGE MASTER statement identifies the binary log file
and the position in that file at the time that the backup file is
created. You use this information later when you set up
replication on the slave server to synchronize the slave
server with the master server.
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23. Configuration Changes on Master
(1)
 Shut down the master server.
 Modify the [mysqld] group in the option file on the master
server to specify a server ID for the master server.
– The master server and any slave servers must each be assigned a
unique numerical ID.
 If you don't want to replicate a specific database, such as the
mysql or test databases, you can add a binlog-ignoredb option for each database to prevent changes to that
database from being logged to the binary file.
 Restart the master server.
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24. Configuration Changes on Master
(2)
 Two binlog-ignore-db options specify
[mysqld]
log-bin
that changes to the mysql and test
binlog-db=sakila
databases should not be logged to
binlog-ignore-db=mysql
the binary files.
binlog-ignore-db=test
server-id=masterserverID;
log-bin option specifies
 The server-id option specifies the
numbered ID for the master server.
 Note: If you use an existing option
that binary logging should
file, a server-id may already be
be enabled.
present. If multiple options are
specified and the numerical IDs are
different, replication might not work.
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25. Configuration Changes on the Slave
 Shut down the slave server.
 Modify the option file on the slave server so that
the [mysqld] section includes the following settings:
server-id=<slave server id>
 Make certain that this server ID is different from the
master server ID and different from any other slave
server IDs. Also be sure that this is the only serverid option defined on the slave server.
 Restart the slave server.
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26. Restore Backup on Slave
 Use the backup file created on Master to load the
databases into the slave server
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27. Set up Connection to Master
 Specify the settings that
will be used for the slave
 Syntax
CHANGE MASTER TO
server to connect to the
MASTER_HOST='<master host>',
master server and
MASTER_USER='<user account>',
determine which binary log
MASTER_PASSWORD='<passwor
file to access. Launch the
mysql client utility on the
slave server, and execute
CHANGE MASTER
statement.
d>',
MASTER_LOG_FILE='<log file>',
MASTER_LOG_POS=<position>;
 The slave server adds this
information to the master.info file,
which is used when connecting to
the master server.
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28. Start Replication on Slave
 The final is to start the replication process on the
slave server. To do so, execute the following SQL
statement on the slave server:
START SLAVE;
 The statement initiates the threads that connect
from the slave server to the master server.
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29. Verifying Replication
 Once replication is set up, update a table on the master
server and then confirm whether that change has been
replicated to the slave server.
 To support administering replication, MySQL provides a
number of SQL statements that allow you to view information
about the replication environment or take a specific action.
MySQL supports statements for both the master server and
the slave server.
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30. Verifying Replication
 Managing the Master Server:
– RESET MASTER Statement
– SHOW MASTER STATUS Statement
– SHOW SLAVE HOSTS Statement
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31. Verifying Replication
 Managing the Slave Server:
– SHOW SLAVE HOSTS Statement
– CHANGE MASTER Statement
– RESET SLAVE Statement
– SHOW SLAVE STATUS Statement
– START SLAVE Statement
– STOP SLAVE Statement
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32. Exercise
 Thực hiện đồng bộ hoá CSDL test của bài trước.
– Cấu hình slave server giả lập trên 1 máy tính
– Bật chế độ --log-bin trên master server
– Backup CSDL test trên master server với option –masterdata
– Tạo người dùng cho slave
– Slave server thực hiện restore CSDL test
– Khai báo thông tin để truy cập bin log thực hiện đồng bộ
hoá
– Bắt đầu tiến hành đồng bộ hoá
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