Aleksander Slominski wrote:
> Gervas Douglas wrote:
>> BTW, the J/JS idea of leasing would be very useful for such a tuple space.
>>
> hi Gervas,
>
> from my experience working with APIs that use leases (and having my own
> implementations of such systems as well including grid systems and my
> own XML tuple space implementation): using the concept of a lease to
Should note, I implemented Blitz JavaSpaces and as I've said elsewhere,
I've done a lot of 'space/jini systems.
> maintain garbage collecting of unused distributed resources is very
> enticing but in practice it leads to all kinds of problems.
>
> issues range from deciding on suitable lease duration/renewal policy to
Is this any different from deciding on any particular timeout for say a
transaction? Noting of course that typically, timeouts tend to be fixed
whilst a lease gives you the ability to extend your use of a resource
until you're done.
In the case of Jini's leasing implementation, the hardest part you have
to deal with is deciding on an initial lease time and how much you wish
to extend by. The core utilities take care of the rest like scheduling
renewals etc.
> actually dealing with large failures - it is not great when some
Can you explain more about what you mean by dealing with large failures?
> resources decide to commit "suicide" because lease was not renewed (not
> mentioning possible domino effect) ...
>
I'm not fully understanding what you're saying here but it sounds to me
like you're maybe using leases the wrong way design-wise. The only kind
of "domino effect" I ever see is as resources reset and user processes
deal with that consequence and restart their work.
There are good examples of leases working very well such as Google's
MapReduce and file system. I'm pretty sure DHCP uses the concept as well.
> i think that for many application i prefer a more manual cleanup/garbage
> collection (as one could say: some app garbage maybe treasure to others
> :) ).
>
This will work fine on a small scale but across 100's of blade servers
and their associated processes, manual is bad, automated is good, it
cuts sysadmin costs for a start both in terms of headcount and expertise.
I do think there's a danger of trying to use leases for everything and
that's a bad thing, I also think there's a danger of using them at too
granular level leading to far too many leases.
> i found myself often using "forever" leases what leases had to be used
> as a workaround (that is completely defeating purpose of leases ...)
>
Not necessarily - some kinds of data do need to "live forever", others
don't.
> best,
>
> alek
>>
Dan.
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