memcached replication

[Aaron Stone]

On Mon, 2007-08-27 at 09:43 -0700, Dustin Sallings wrote:
> On Aug 27, 2007, at 4:39 , Wojtek Meler wrote:
> 
> > I think memcached server should be able to broadcast some kind of  
> > update
> > log that other instances would listen. It would also enable event
> > notification on state changes.
> > Anyone interrested in such feature ?
> 
> 	I'm somewhat interested in being able to connect to an instance and  
> have it start feeding me notifications for anything that would  
> invalidate the cache for a particular key.
> 
> 	I haven't got around to doing anything about it, though.

I have thought about doing this, too -- the issues I'm raising are the
ones that were raised to me when I started talking about the idea...

A major design goal of memcache is to have all operations be roughly
order 1. A notification system would be order n with the number of
listeners on that key. Also, where would the memory for keeping track of
listeners go?

I had originally thought that this would make the most sense with
per-key notifications. Maybe it would be better to do this as a global
notification system? That might entail adding one new keyword to the
protocol which puts a TCP session into notification mode until the end
of the session.

Aaron