Memcached PHP Sessions

[BUSTARRET, Jean-Francois]

> > Plus session handling has a large impact on load-balancer 
> CPU, and a CPU-starved load-balancer has an impact on all 
> your HTTP traffic (even the one that does not need sessions, 
> ie static content).
> >
> 
> TCP/HTTP Load Balancer, such as HA proxy, use a single-process,
> event-driven model which considerably reduces the cpu usage even under
> high load, not difficult to saturate your network bandwidth with
> modern CPU.

I was speaking for LARGE sites. I don't think your HA proxy will handle
30k HTTP requests/s (or 100k TCP sessions) with Layer 7 processing
(parsing cookies and so on).
If you have to spend 100k$ on a pair of hi-end load-balancers just to
handle session affinity (without 100% reliability), or spend 2GB of RAM
to store session in memcached (without 100% reliability), what is the
most cost effective solution ?

I'm not telling memcached is THE solution, but something that must be
considered (cost wise). IMHO, memcached as a session cache with a DB
backend would me much safer (if your sessions are not updated too
often).