DCONF(7) Conventions and miscellaneous DCONF(7)NAMEdconf - A configuration systen
DESCRIPTIONdconf 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.
PORTABILITYdconf 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 ALSOdconf-service(1), dconf-editor(1), dconf(1), GSettings[1]
NOTES
1. GSettings
http://developer.gnome.org/gio/stable/GSettings.html
dconfDCONF(7)