Perlbal and sessions.

Mark Smith marksmith at
Sat Feb 26 14:13:04 PST 2005

State is accessible from every node.  Requests come in with a session
cookie, and the web node asks memcache to see if it knows anything about
that session.  It falls back on the databases if memcache has no
information on that cookie.

Most of our infrastructure is replaceable and non-unique.  Our storage
nodes are all duplicated through Mogile, our load balancers are identical,
our web nodes all do the same things, etc.  The only parts of the system
that can't just be swapped out at will are the databases -- but they get
redundancy through having two machines doing the same load with only one
active at a time.

On Sat, Feb 26, 2005, christopher at wrote:
> >No, it doesn't really have any concept of that.  It sends requests to
> > available nodes in a pool, that's it.  :)
> Are LiveJournal requests are completely stateless or can the state can be
> accessed from any node?  Maybe that's what memcached is all about.  Just
> query the state on every hit.  I wonder how common this is.  Obviously it
> is a good way to scale up.
> Christopher Baus

Mark Smith
junior at

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