Re: New module proposal: tracker

[Philip Van Hoof <spam pvanhoof be>]

On Fri, 2009-11-06 at 20:24 +0100, Alexander Larsson wrote:
 
> > > I understand that this is not nice :(. But indeed, tracker-store isn't
> > > system-wide, instead it's per user.
> > 
> > That won't work because you won't have access to the session D-Bus, and
> > certainly wouldn't work with, say, 1k users with NFS home dirs.
> 
> Not to mention LDAP/NIS or things like that.
> 
> Its not what you want to do anyway. You want to ship the package with a
> set of indexes for its help, and then when doing the query for help you
> want to say "search for this string in these given installed index
> files".

A system-wide database for a user's service will come down to using
ATTACH in sqlite (that we use internally to translate your SPARQL to).

This works nice but the problem is that we'd need to do a UNION on the
query to ensure that we involve the system-wide db's tables in it.

We already cache the sqlite3_stmt objects so that's not the problem with
it, but UNION of course does mean that the query gets executed twice. 

And because we don't know when to UNION or not, we'd always have to do
this. Meaning that all of our queries would become two times slower.

We could of course start supporting a light form of named graphs[1] and
then we could based on the selected graph select data out of a system
wide database instead. We currently have no plans for this, though.

It would look like this:

SELECT ?title FROM NAMED tracker:system-wide 
WHERE { ?a a gnome:ManPage ; nie:title ?title . }

This kind of feature is of course something we'd have to decide as a
team. Although I'd personally like it I can't promise that we'll
implement something like this.

But I'll bring up to issue of system-wide data versus deployment on
large scale systems with thousands of users, in one of our meetings.

Thanks for the use case.

--- 
[1] http://www.w3.org/TR/rdf-sparql-query/#namedGraphs


-- 
Philip Van Hoof, freelance software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://pvanhoof.be/blog
http://codeminded.be