A Berkeley DB environment is an encapsulation of one or more databases, log files, region files and configuration files. The Berkeley DB environment has its own set of default configuration values for things like the number of database locks allowed to be taken out at any given time, or the maximum size of the journaling log files, etc. Subversion's filesystem logic additionally chooses default values for some of the Berkeley DB configuration options. However, sometimes your particular repository, with its unique collection of data and access patterns, might require a different set of configuration option values.

The producers of Berkeley DB understand that different applications and database environments have different requirements, and so they have provided a mechanism for overriding at runtime many of the configuration values for the Berkeley DB environment: BDB checks for the presence of a file named DB_CONFIG in the environment directory (namely, the repository's db subdirectory), and parses the options found in that file . Subversion itself creates this file when it creates the rest of the repository. The file initially contains some default options, as well as pointers to the Berkeley DB online documentation so you can read about what those options do. Of course, you are free to add any of the supported Berkeley DB options to your DB_CONFIG file. Just be aware that while Subversion never attempts to read or interpret the contents of the file, and makes no direct use of the option settings in it, you'll want to avoid any configuration changes that may cause Berkeley DB to behave in a fashion that is at odds with what Subversion might expect. Also, changes made to DB_CONFIG won't take effect until you recover the database environment (using svnadmin recover).