Mysql

Replication enables data from one MySQL database server (called the master) to be replicated to one or more MySQL database servers (slaves). Replication is asynchronous - your replication slaves do not need to be connected permanently to receive updates from the master, which means that updates can occur over long-distance connections and even temporary solutions such as a dial-up service. Depending on the configuration, you can replicate all databases, selected databases, or even selected tables within a database.
The target uses for replication in MySQL include:
Scale-out solutions - spreading the load among multiple slaves to improve performance. In this environment, all writes and updates must take place on the master server. Reads, however, may take place on one or more slaves. This model can improve the performance of writes (since the master is dedicated to updates), while dramatically increasing read speed across an increasing number of slaves.
Data security - because data is replicated to the slave, and the slave can pause the replication process, it is possible to run backup services on the slave without corrupting the corresponding master data.
Analytics - live data can be created on the master, while the analysis of the information can take place on the slave without affecting the performance of the master.
Long-distance data distribution - if a branch office would like to work with a copy of your main data, you can use replication to create a local copy of the data for their use without requiring permanent access to the master.
Replication in MySQL features support for one-way, asynchronous replication, in which one server acts as the master, while one or more other servers act as slaves. This is in contrast to the synchronous replication which is a characteristic of MySQL Cluster (see Chapter 16, MySQL Cluster).
There are a number of solutions available for setting up replication between two servers, but the best method to use depends on the presence of data and the engine types you are using. For more information on the available options, see Section 15.1.1, “How to Set Up Replication”.
Replication is controlled through a number of different options and variables. These control the core operation of the replication, timeouts and the databases and filters that can be applied on databases and tables. For more information on the available options, see Section 15.1.2, “Replication Startup Options and Variables”.
You can use replication to solve a number of different problems, including problems with performance, supporting the backup of different databases and for use as part of a larger solution to alleviate system failures. For information on how to address these issues, see Section 15.2, “Replication Solutions”.
For notes and tips on how different data types and statements are treated during replication, including details of replication features, version compatibility, upgrades, and problems and their resolution, including an FAQ, see Section 15.3, “Replication Notes and Tips”.

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