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MySQL 5.7 Reference Manual  /  Alternative Storage Engines  /  The FEDERATED Storage Engine

15.8 The FEDERATED Storage Engine

The FEDERATED storage engine lets you access data from a remote MySQL database without using replication or cluster technology. Querying a local FEDERATED table automatically pulls the data from the remote (federated) tables. No data is stored on the local tables.

To include the FEDERATED storage engine if you build MySQL from source, invoke CMake with the -DWITH_FEDERATED_STORAGE_ENGINE option.

The FEDERATED storage engine is not enabled by default in the running server; to enable FEDERATED, you must start the MySQL server binary using the --federated option.

To examine the source for the FEDERATED engine, look in the storage/federated directory of a MySQL source distribution.

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User Comments
  Posted by Steven Hartland on March 18, 2011
Optional storage engines require privileges and will fail to load when --skip-grant-tables is specified.

The result the entire db will fail to load and the following error will appear in the logs:
110318 21:37:23 [ERROR] /usr/local/libexec/mysqld: unknown option '--federated'

This in turn means that an upgrade from 5.x needs to be done in two steps if you have federated tables. Once with --skip-grant-tables and without --federated, the once without --skip-grant-tables and with --federated.
  Posted by ALEXANDER SKAKUNOV on January 8, 2013
This is very powerful tool for deployment, especially if you have vital data that you use in many projects (databases) on the same server.

Examples are any dictionaries: IP to location, Geographical hierarchy, list of points of interest, etc. For instance, on it's used to work with fresh currency rates across a few connected projects.
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