groups of keys and dependent keys

[Paul T]

The efficient implementation of 'namespaces' is
described here :

http://lists.danga.com/pipermail/memcached/2006-July/002551.html

No need to broadcast nothing, the expiration is
effectievly client side. 

No substantial impact on performance either.

Rgds.Paul.

> A key and its dependencies may be spread across
> multiple servers, 
> memcached being a distributed system. How will a
> server know when it's 
> safe to delete something? Bear in mind that at some
> installations (ours 
> included, but others as well) "multiple servers"
> means well in excess of 
> 100, so "broadcast to all the other servers when
> something happens" is 
> not an option unless you're VERY frugal in the use
> of broadcasts.
> 
> What happens when a server with one of the dependent
> keys crashes or its 
> memcached instance is restarted?
> 
> Can you set different expiration times on different
> keys in a dependency 
> graph? What happens if the parent key's expiration
> time passes and you 
> try to fetch a child key? (Expiration is lazy in
> memcached.)
> 
> What will the performance impact be on operations
> not involving key 
> dependencies? Busy memcached installations handle a
> couple tens of 
> thousands of requests a second, so whatever the
> implementation for this 
> looks like, it needs to be able to keep up with that
> kind of load.
> 
> Don't get me wrong -- if what you describe can be
> made to work well, it 
> will definitely be useful! But I suspect it'll be
> trickier than it 
> appears to make it bulletproof.
> 
> -Steve
> 
> 
> Martin Kihlgren wrote:
> > Hello list.
> >
> > My name is Martin Kihlgren, and I am currently
> employed by a company
> > that heavily relies on memcached.
> >
> > We are doing lots of caching, simply.
> >
> > And, unfortunately, a whole lot of invalidations.
> >
> > Today we got to know of
> >
>
http://search.cpan.org/dist/Cache-Memcached-Managed/lib/Cache/Memcached/Managed.pm#SYNOPSIS
> > and I thought about the implications.
> >
> > It would be so very much nicer to have this
> functionality built into
> > memcached :O
> >
> > The scheme I would imagine is:
> >
> >  * The addition of key dependency, in at least one
> level.
> >    * A key can be declared depending on another
> key.
> >  * A key can not be dropped unless all keys
> depending on it are
> >    dropped.
> >    * If a key having dependent keys MUST be
> dropped, the whole
> >      set of dependent keys are dropped as well.
> >
> > This would make it very easy for us to create
> group keys having
> > dependent keys, and then just delete the group key
> thus forcing all
> > dependent keys to be dropped.
> >
> > Much simpler and more efficient than storing the
> set of keys in the
> > group in memcache (thus having to worry about
> memcache dropping the
> > group key before the individual keys in the group
> are dropped) and
> > also much better than storing the group keys on
> disk or in db.
> >
> > Is this something you have discussed? Or is it
> already in some edge
> > version of memcached? Or is it something that is
> possible to do with
> > the current codebase?
> >
> > regards,
> > //Martin Kihlgren
> >
> >   
> 
> 


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