Reserved memcached key namespace

[Marc]

Lately it seems to me that it would be a lot easier to add features and keep
clients small and simple if we used a reserved part of the memcached key
namespace for admin and status operations.  Consider stats, version,
flush_all and flush_regex.  Rather than implementing a new message format,
one would simply set or get keys from the reserved namespace.

   quit\r\n

   becomes:

   set __quit__ 0 0\r\n\r\n =>
       <= STORED\r\n

   version\r\n

   becomes:

   get __version__\r\n =>
       <= VALUE __version__  0 9\r\n1.2.0-rc1\r\nEND\r\n

For something like stats, there should be a key whose value is all the stat
keys recognized by that server.  Ie

   get __stat_keys__\r\n =>
       <= VALUE __stat_keys__ 0 329\r\n__pid__ __uptime__...\r\nEND\r\n

One could then mget some or all stats:

   get __pid__ __uptime__ __time__\r\n

For multiparameter admin command like 'stats cachedump' some standard
parameter delimiter syntax can  be used.  Ie

   get __cachedump__?id&limit\r\n

This could be done very efficiently on the server side.  Basically once the
reserved prefix is identified, just tokenize the key and fork off to the
existing stats/admin command handling functions.  They'd have to be tweaked
somewhat for the new format.  The main thing would be to documents required
and optional well-known keys in the protocol spec.

I'm interested in prototyping this.  I wanted to get a sense of people's
interest and if there are any obvious choices for a reserved-key
prefix/suffix that won't conflict with current installations.