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We've encountered a couple use cases where having federated tables prove useful, despite their limitations and caveats.

As best I can tell this must be enabled with a federated declaration in the .cnf upon startup.

Our use cases are limited and certainly don't warrant restarting every instance just to have it. At the same time I'm thinking of adding it as a default to our standard config so it is available on instances as they get bounced during more pressing maintenance.

Is there any reason not to have this option available unless decided absolutely necessary?

For a final clarification: This question is not about the disadvantages of actually using a federated engine; rather it is just about just enabling as an available option. Perhaps to put it another way: Is there good reason it is disabled by default other than making sure you don't shoot yourself in the foot if you understand the consequences?

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1 Answer 1

IMHO it is really about security. If a table uses the federated storage engine, all one needs to do is this :

SHOW CREATE TABLE fedtblname\G

and you can see the connection information (server IP, database, table name, username, password) of the real MyISAM table on the remote DB server, and all in plain text.

It is too bad that the connection information is not encrypted.

The bottom line is that you can use federated option in my.cnf totally at your own risk.

UPDATE 2012-01-18 11:31 EDT

It was pointed out that you can create a server definition and then define that server definition in the CONNECTION option of the federated table.

I tested this out and it works great.

However, there is still a security flaw. If you can SELECT from the table mysql.servers, you can see all definitions. Here is the table's layout:

mysql> show create table mysql.servers\G
*************************** 1. row ***************************
       Table: servers
Create Table: CREATE TABLE `servers` (
  `Server_name` char(64) NOT NULL DEFAULT '',
  `Host` char(64) NOT NULL DEFAULT '',
  `Db` char(64) NOT NULL DEFAULT '',
  `Username` char(64) NOT NULL DEFAULT '',
  `Password` char(64) NOT NULL DEFAULT '',
  `Port` int(4) NOT NULL DEFAULT '0',
  `Socket` char(64) NOT NULL DEFAULT '',
  `Wrapper` char(64) NOT NULL DEFAULT '',
  `Owner` char(64) NOT NULL DEFAULT '',
  PRIMARY KEY (`Server_name`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='MySQL Foreign Servers table'
1 row in set (0.00 sec)

mysql>

In order to see the server definitions, run this query:

SELECT * FROM mysql.servers\G

This will expose all remote servers known by the MySQL Instance, including the password in plain text.

To see all the federated tables, run this:

select table_schema,table_name from information_schema.tables where engine='federated';

This confirms my original assertion: all one needs to do is this :

SHOW CREATE TABLE fedtblname\G

and you can see the connection information (server IP, database, table name, username, password) of the real MyISAM table on the remote DB server, and all in plain text. As given by my update, that plain text info is located in mysql.servers.

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This isn't completely true. You can create a connection using the create server command: dev.mysql.com/doc/refman/5.1/en/create-server.html. Then in your schema definition you can specify "connection='myserver/tablename'" leaving the credentials hidden. I believe this was added in 5.1 –  atxdba Jan 18 '12 at 13:18

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