In the previous list of articles, I demonstrated FEDERATED storage engine to perform cross-server queries between MySQL Servers.

MySQL: Create FEDERATED Table to SELECT data from another server (Part 3/4)

In this post, I am showing to create the Connection Server and use that Server detail with multiple FEDERATED Table of MySQL.

Without a Connection server, we need to write the connection string in every FEDERATED table so when we have a multiple FEDERATED table and which are using same remote connection information, create Connection Server once and use with all tables.

Below is a small demonstration.

First Create a Server:

CREATE SERVER FederatedConnectionServer
FOREIGN DATA WRAPPER mysql
OPTIONS (USER 'UserName',password 'Password', HOST 'localhost', PORT 3306, DATABASE 'TestDB');

Now use this server information to create Remote FEDERATED Table:

CREATE TABLE tbl_RemoteTable 
(
    ID integer
    ,Name VARCHAR(255)
) 
ENGINE=FEDERATED
CONNECTION='FederatedConnectionServer/tbl_RemoteTable';

This is the last part of the series on the FEDERATED Table of MySQL, so in this post, I am sharing important Notes and Tips of FEDERATED Engine.

• The remote server must be a MySQL Server.
• You can replicate the FEDERATED table to other slaves, but ensure that slave server is able to use defined connection string.
• You can create nested FEDERATED tables.
• The FEDERATED table does not support indexes because of its virtual nature.
• The FEDERATED storage engine supports SELECT, INSERT, UPDATE, DELETE, TRUNCATE TABLE.
• The FEDERATED also supports INSERT ON DUPLICATE KEY UPDATE statements.
• The FEDERATED table does not support Transaction.
• The FEDERATED table can also perform bulk-insertion.
• Any DROP TABLE statement issued against a FEDERATED table drops only the local table, not the remote table.
• The FEDERATED tables do not work with the query cache.

For more info, You can visit this MySQL official document.

In the previous post, we have seen a basic theory and configuration of FEDERATED table. In this post, I am going to create a FEDERATED table which is used to SELECT data from another MySQL Server.

How to create FEDERATED Tables?

Assume that we have two running servers, either both on the same host or different hosts.

For example:

Server – A108 (Remote MySQL Server)
Server – B108 (Local MySQL Server)

We need to execute the SELECT command from Server B108 and fetching data from Server A108.
Here, Server A108 is a remote server and Server B108 is a local server.

Now create a sample table in Server A108.

CREATE TABLE tbl_RemoteTable 
(
    ID integer
    ,Name VARCHAR(255)
) 
ENGINE=InnoDB;

Now, create a FEDERATED table in Server B108 to SELECT data from Server A108.
You have to specify FEDERATED engine with remote CONNECTION information.

CREATE TABLE tbl_RemoteTable 
(
    ID integer
    ,Name VARCHAR(255)
) 
ENGINE=FEDERATED
CONNECTION='mysql://root:root@localhost:3306/B108/tbl_RemoteTable';

As you can see, I created FEDERATED table into Local Server B108 using the connection information of Remote Server A108.

You can access this table like any other table, and if any data insert or delete in remote Table, it automatically updates here because this is a virtual table.

Below are different format of connection strings:

CONNECTION='mysql://username:password@hostname:port/database/tablename'
CONNECTION='mysql://username@hostname/database/tablename'
CONNECTION='mysql://username:password@hostname/database/tablename'

In the previous post, I shared a basic theory on the FEDERATED Table Engine.

As earlier I discussed that, FEDERATED Engine is not by default enabled so In this post; I am giving basic commands to enable and configure FEDERATED Table Engine.

First Check FEDERATED engine is available or not:

SHOW ENGINES;

Using above commands, we can get all available engines.
In the above image, you cannot find a FEDERATED engine, so we need to install it.

Command to enable federated engine.

install plugin federated soname 'ha_federated.so'

Now check all engines details:

In the above result, we can find a new entry of FEDERATED engine, but still, it is OFF.

To enable this, we need to add a federated line into my.cnf file

Command to open my.cnf file:

sudo nano /etc/my.cnf

Write federated into this file:

[mysqld]
  datadir=/var/lib/mysql
  socket=/var/lib/mysql/mysql.sock
  user=mysql
  # Disabling symbolic-links is recommended to prevent assorted security risks
  symbolic-links=0
  federated

  [mysqld_safe]
  log-error=/var/log/mysqld.log
  pid-file=/var/run/mysqld/mysqld.pid

Restart Mysqld:

sudo service mysqld restart

Now check all engines details and find FEDERATED engine is ON:

In this post, I am going to start a small series of articles which divided into four different parts.

In this set of articles, I will provide basic theory and practical to perform cross-platform or cross-server queries in MySQL. We can also say remote queries.

Some of the Database Professional already aware about Linked server object of Microsoft SQL Server, which is used for cross-server queries.
Many times, we need to SELECT data from the different database server and even, we require to fetch data from various RDBMS products as well.

MySQL also provides the FEDERATED Storage Engine to access data from a remote MySQL Database Server.

The FEDERATED Storage Engine is available beginning with MySQL 5.0.3.

We don’t require to write any database level trigger to update real-time data into the local FEDERATED table because it is fetching data remotely and even does not need to store that data physically on the hard disk.

We can query to the local FEDERATED table like any other normal table, but it is working as a virtual table only.

The FEDERATED storage engine is not enabled by default in the running server.
You can visit the next article to configure and enable FEDERATED Engine.