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The DB_CONFIG File
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## The DB_CONFIG File

You can configure most aspects of your Berkeley DB environment by using the `DB_CONFIG` file. This file must be placed in your environment directory. When using the BDB SQL interface, this is the directory created alongside of your database. It has the same name as your database, followed by a `-journal` extension. For example, if your database is named `mydb.db`, then your environment directory is created next to the `mydb.db` file, and it is called `mydb.db-journal`.

If a `DB_CONFIG` file exists in your environment directory, it will be read when your environment is opened. This happens when your application starts up and creates its first connection to the database.

Configurations set in the DB_CONFIG file usually appear as the name of the configuration's C function, as documented in Berkeley DB C API Reference Guide, followed by the values of the function arguments. For example, you can use the set_lg_dir DB_CONFIG parameter to configure the directory in which log files are stored like this:

    set_lg_dir ../myLogDir

In some cases, you must either specify a configuration option before the environment is created, or the environment must be re-created before the configuration option will take effect. The documentation for each configuration option will indicate where this is true.

### Creating the DB_CONFIG File Before Creating the Database

In order to provide the `DB_CONFIG` file before the database is first created, physically make the journal directory in the correct location in your filesystem (this is wherever you want to place your database file), and put the `DB_CONFIG` file there before you create your database. For example, if you plan to create a database named `mydb.db`, then in the same directory as the database, create a directory named `mydb.db-journal`.

### Re-creating the Environment

Some `DB_CONFIG` parameters require you to re-create your environment before they take effect. The `DB_CONFIG` parameter descriptions indicates where this is the case.

To re-create your environment:

- Make sure the `DB_CONFIG` file contains the following line:

      add_data_dir ..

  (This line should already be in the `DB_CONFIG` file.)

- Run the db_recover command line utility. If you run it from within your environment (`-journal`) directory, no command line arguments are required. If you run it from outside your environment directory, use the `-h` parameter to identify the location of the environment directory:

      db_recover -h /some/path/to/mydb.db-journal

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