Performance of DBUS with multiple nodes

[Havoc Pennington]

Hi,

Jacques Guillou wrote:
> The questions :
> Does the DBus forwarding performance decrease when many nodes are 
> registered to the bus ?

I'm assuming by "node" you mean object path?

If you mean bus name, then there is probably some performance 
implication to having thousands of them, yes. I don't know how bad it 
would be. I don't think it will be O(n) but maybe something is - if so 
it could be fixed. It may use memory though.

If you mean object path, then those are not registered by the bus at 
all, so there's zero impact on the bus.

There are two ways to do object paths with libdbus:
  - register each one separately with DBusConnection; in this case, each 
one will use memory
  - register a handler for your "subtree" with DBusConnection, which 
will use one fixed small amount of memory; then parse the rest of the 
object path after the common prefix yourself - this should be efficient 
up to any number of object paths, as long as your app code is efficient

> What about the memory usage ? Is the introspection data stored for each 
> node in the daemon itself or is it accessed on demand ?

Introspection data is never kept around by libdbus or dbus-daemon

For all of the above, there may be issues specific to the language 
binding you are using, in addition to the raw libdbus/dbus-daemon answer.

Havoc