DCONF(7)

NAME
dconf - A configuration systen

DESCRIPTION

dconf is a simple key/value storage system that is heavily optimised for reading. This makes it an ideal system for storing user preferences (which are read 1000s of times for each time the user changes one). It was created with this usecase in mind.

All preferences are stored in a single large binary file. Layering of preferences is possible using multiple files (ie: for site defaults). Lock-down is also supported. The binary file for the defaults can optionally be compiled from a set of plain text keyfiles.

dconf has a partial client/server architecture. It uses D-Bus. The server is only involved in writes (and is not activated in the user session until the user modifies a preference). The service is stateless and can exit freely at any time (and is therefore robust against crashes). The list of paths that each process is watching is stored within the D-Bus daemon itself (as D-Bus signal match rules).

Reads are performed by direct access (via mmap) to the on-disk database which is essentially a hashtable. For this reason, dconf reads typically involve zero system calls and are comparable to a hashtable lookup in terms of speed. Practically speaking, in simple non-layered setups, dconf is less than 10 times slower than GHashTable.

Writes are assumed only to happen in response to explicit user interaction (like clicking on a checkbox in a preferences dialog) and are therefore not optimised at all. On some file systems, dconf-service will call fsync() for every write, which can introduce a latency of up to 100ms. This latency is hidden by the client libraries through a clever "fast" mechanism that records the outstanding changes locally (so they can be read back immediately) until the service signals that a write has completed.

PORTABILITY

dconf mostly targets Free Software operating systems. It will theoretically run on Mac OS but there isn't much point to that (since Mac OS applications want to store preferences in plist files). It is not possible to use dconf on Windows because of the inability to rename over a file that's still in use (which is what the dconf-service does on every write).

API STABILITY

The dconf API is not particularly friendly, and is not guaranteed to be stable. Because of this and the lack of portability, you almost certainly want to use some sort of wrapper API around it. The wrapper API used by GTK+ and GNOME applications is GSettings[1], which is included as part of GLib. GSettings has backends for Windows (using the registry) and Mac OS (using property lists) as well as its dconf backend and is the proper API to use for graphical applications.

SEE ALSO

dconf-service(1), dconf-editor(1), dconf(1), GSettings[1]

AUTHOR

Ryan Lortie <desrt@desrt.ca>

    Developer

REFERENCES

1.  GSettings
    http://developer.gnome.org/gio/stable/GSettings.html