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Configuring Mnesia

Mnesia is packaged as an OTP application. To use it, you usually create an empty schema that is stored on disk. But you can also use Mnesia as a RAM-only database that only keeps its schema in RAM. Having created a schema, you need to start Mnesia and create the tables. Once they are created, you can read and manipulate your data. You need to create your schema and tables only once, usually when installing your system. When you’re done, you can just start your system, together with Mnesia, and all persistent data will become available.

Setting Up the Schema

A schema is a collection of table definitions that describe your database. It covers which of your tables are stored on RAM, disk, or both, alongside their configuration characteristics and the format of the data they will contain. These characteristics may differ from node to node, as you might want your table to have its disk copies on the operation and maintenance node but have RAM-only copies on the transaction nodes. In Erlang, the schema is stored in a persistent Mnesia table. When configuring your database, you create an empty schema table which, over time, you populate with your table definitions.

To create the schema,[32] start your distributed Erlang nodes and connect them. If you do not want to distribute Mnesia, just start a non-distributed Erlang node. Before doing this it is important to make sure no old schemas exist, as well as ensuring that Mnesia is not started.

In our example, we will be starting ...

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