Re: [Tracker] Simplifying DBus interface

[Jamie McCracken <jamiemcc blueyonder co uk>]

Samuel Cormier-Iijima wrote:
> I don't think we need to hide how the database is structured
> internally - we're talking about open source here anyways :-), and
> somebody can just access the database directly. Actually, I was
> talking with thiago on #dbus and he had this to say:
>
> thiago: I mean, there's nothing wrong in developing a backend for a
> service that uses D-Bus to talk to a daemon
> thiago: I just wonder why people develop new libraries doing that
> instead of simply developing the daemon and the API
> yoshiznit123: just for simplicity, as you said vanilla dbus is pretty 
> difficult
> thiago: right, but the XML is much simpler
> yoshiznit123: xml? we have the introspection file if that's what you 
> mean...
> thiago: yep
> thiago: if your library is just a thin-wrapper around the XML, I see
> no need for the library
> thiago: if it does something more involved, then it makes sense.
> yoshiznit123: yea, i think we have a wrapper around the header created
> by dbus-binding-tool
> yoshiznit123: :-)
> thiago: that's my point: if we can recreate your library using a code
> generator, then we don't need a library :-)
> yoshiznit123: yea, i'll point that out to jamie

we have a thin wrapper in libtracker to remove DBUS'isms only.

> thiago: IMO, it makes sense to have a library when D-Bus is just one
> of many (possible) backends
> thiago: for instance, libtracker could open the SQLite database
> directly and avoid the daemon
> thiago: in that case, it makes sense to have a library
>
> Would it be better to extend libtracker to allow direct mysql queries
> (bypass dbus completely)? i thought that would have a few problems,
> such as database locking

cant do with embedded mysql as it exclusively locks the DB so only one 
process can access it

Sqlite allows but will corrupt on NTFS with broken file locking (with a 
daemon it will use mutexes to prevent this and the tracker daemon can 
also use an external lock file to prevent corruption on multiple session 
NTFS)

 and pulling in libmysqlclient or sqlite as a
> dependency on libtracker, and i'm not sure it would provide many
> advantages... the reason is because dbus wouldn't be able to handle
> queries sent over dbus with really big result sets...

We would need some sort of limit applied so that say no more than 4096 
rows are dispatched coded into the dbus method. Select queries in both 
mysql and sqlite also have limit and offset as part of their sql 
language so you can say "select * from Services limit 1024" and the 
query will deliver the first 1024 rows only.

--
Mr Jamie McCracken
http://jamiemcc.livejournal.com/