Friday, February 20, 2009

MySQL 5.0 Replication

Replication is having the data from a Master unit copy to the backup unit(s) automatically. In this demonstration I actually used a Linux MySQL to replicate to a Mac OS X Database server every 5 minutes.

Let's say you have 2 MySQL servers (Production and Read-Only Backup). How would you get the information automatically from the production unit to the backup unit.

I believe that the my.cnf is typically in the same place across all NIX OSes.
nano /etc/my.cnf
Make sure and check the location of the my.cnf file and that you have mysql installed. This will not work for MySQL 4.x version and it has been a few months since I have built thing but everything should work fine. I also recommend before you do anything that you make sure and backup your databases before you begin.

Edit the my.cnf file using either VI or Nano I always use nano even though it is not better then VI
#Example MySQL config file for very large systems.
# This is for a large system with memory of 1G-2G where the system runs mainly
# MySQL.
# You can copy this file to
# /etc/my.cnf to set global options,
# mysql-data-dir/my.cnf to set server-specific options (in this
# installation this directory is /var/mysql) or
# ~/.my.cnf to set user-specific options.
# In this file, you can use all long options that a program supports.
# If you want to know which options a program supports, run the program
# with the "--help" option.

# The following options will be passed to all MySQL clients
#password       = your_password
port            = 3306
socket          = /var/mysql/mysql.sock

# Here follows entries for some specific programs

# The MySQL server
port            = 3306
socket          = /var/mysql/mysql.sock
key_buffer = 384M
max_allowed_packet = 100M
table_cache = 512
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size = 8
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency
thread_concurrency = 8

# Don't listen on a TCP/IP port at all. This can be a security enhancement,
# if all processes that need to connect to mysqld run on the same host.
# All interaction with mysqld must be made via Unix sockets or named pipes.
# Note that using this option without enabling named pipes on Windows
# (via the "enable-named-pipe" option) will render mysqld useless!

# Replication Master Server (default)
# binary logging is required for replication

# required unique id between 1 and 2^32 - 1
# defaults to 1 if master-host is not set
# but will not function as a master if omitted
server-id       = 2

# Replication Slave (comment out master section to use this)
# To configure this host as a replication slave, you can choose between
# two methods :
# 1) Use the CHANGE MASTER TO command (fully described in our manual) -
#    the syntax is:
#    MASTER_USER=<user>, MASTER_PASSWORD=<password> ;
#    where you replace <host>, <user>, <password> by quoted strings and
#    <port> by the master's port number (3306 by default).
#    Example:

#    MASTER_USER='slave', MASTER_PASSWORD='password';
# OR
# 2) Set the variables below. However, in case you choose this method, then
#    start replication for the first time (even unsuccessfully, for example
#    if you mistyped the password in master-password and the slave fails to
#    connect), the slave will create a file, and any later
#    change in this file to the variables' values below will be ignored and
#    overridden by the content of the file, unless you shutdown
#    the slave server, delete and restart the slaver server.
#    For that reason, you may want to leave the lines below untouched
#    (commented) and instead use CHANGE MASTER TO (see above)
# required unique id between 2 and 2^32 - 1
# (and different from the master)
# defaults to 2 if master-host is set
# but will not function as a slave if omitted
server-id       = 2
# The replication master for this slave - required
master-host     =
# The username the slave will use for authentication when connecting
# to the master - required
master-user     =   slave
# The password the slave will authenticate with when connecting to
# the master - required
master-password =   password
# The port the master is listening on.
# optional - defaults to 3306
#master-port     =  <port>
# binary logging - not required for slaves, but recommended

# Point the following paths to different dedicated disks
#tmpdir         = /tmp/
#log-update     = /path-to-dedicated-directory/hostname

# Uncomment the following if you are using BDB tables
#bdb_cache_size = 384M
#bdb_max_lock = 100000

# Uncomment the following if you are using InnoDB tables
innodb_data_home_dir = /var/mysql/
innodb_log_group_home_dir = /var/mysql/
innodb_log_arch_dir = /var/mysql/
# You can set .._buffer_pool_size up to 50 - 80 %
# of RAM but beware of setting memory usage too high
innodb_buffer_pool_size = 384M
innodb_additional_mem_pool_size = 20M
# Set .._log_file_size to 25 % of buffer pool size
innodb_log_file_size = 100M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 50

#Tells the slave thread to restrict replication to the specified database. 
#To specify more than one database,use the directive multiple times, 
#once for each database.
#Hostname or IP of the slave to be reported to to the master during 
#slave registration. Will appear in the output of SHOW SLAVE HOSTS.
#Leave unset if you do not want the slave to report the name
#This username will be displayed in the output of "SHOW SLAVE HOSTS".
#This password will be displayed in the output of "SHOW SLAVE HOSTS".
#Don't cache host names.
#Don't resolve hostnames. All hostnames are IP's or 'localhost'.

#If set, allows showing user and password via SHOW SLAVE HOSTS
#on master.
#Number of seconds to wait for more data from a master/slave 
#connection before aborting the read
#Tells the slave to log the updates from the slave thread to the binary 
#log. You will need to turn it on if you plan to daisy-chain the slaves.
#The number of seconds the slave thread will sleep before retrying to
#connect to the master in case the master goes down or the connection is lost.

max_allowed_packet = 16M

# Remove the next comment character if you are not familiar with SQL

key_buffer = 256M
sort_buffer_size = 256M
read_buffer = 2M
write_buffer = 2M

key_buffer = 256M
sort_buffer_size = 256M
read_buffer = 2M
write_buffer = 2M

Don't worry if this is a bit tricky, I will be building a new replica again in the very near future with the latest version of MySQL and detailing the entire process from beginning to end.

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