On Thu, May 04, 2006 at 08:46:01AM -0700, Bart Smaalders wrote:
> >http://beaglewiki.org/Main_Page
> >
> >as well as some other GNOME things, apparently.
>
> This cannot scale.
It doesn't necessarily need to scale; from my understanding, Beagle is more
about watching ~/Documents/ than big lots of data.
> >Does this mean we don't get told /what/ got created? Is an application that
> >wants to know "what files are disappearing/appearing under /foo/bar/?" going
> >to have to readdir() the whole directory every time it gets an event?
>
> Otherwise we get into the queued event problem; what happens if the
> application is watching a directory w/ a million files, and someone does
> rm * in that directory? Do we generate a million events? Clearly there
> are limits to the number of events we can queue in the kernel, esp.
> since the application isn't obligated to read them in a timely fashion.
Forcing a (recursive!) readdir() every time can't scale either; it just pushes
the problem out all the userspace apps. Perhaps a compromise approach would
work, so at least the readdir() cost is amortized; i.e. give names up to a
particular limit.
Or how do you expect Beagle to be able to work nicely? Is this just going to
remain something explicitly unsupportable?
> I'd rather have a model like signals; multiple file writes are combined
> into one event until that event is read by the application; any
> subsequent writes generate another event.
Would work fine for modifications, yes.
> I see this as very useful to avoid the {sleep(); stat() } loops we often
> see. It's not a mechanism to insert an application as an synchronous
> interposer into the filesystem VOPS.
I wasn't trying to suggest it was. Synchronisation is neither needed nor
wanted.
> The nscd could use this to watch for modifications to configuration
> files rather than stat'ing them before each cache lookup.
I wasn't suggesting that a non-recursive approach doesn't solve a whole class
of such situations; it does. In fact, I was merely trying to raise awareness of
what applications like Beagle actually need in terms of notifications. If it's
really too hard to do, that's a pity.
regards,
john
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