[Zope] SQLSession vs FSSession for ultra-high scalability and speed.

[chas]

Hi Folks,

Sorry if this has been asked before, but can anybody 
advise on FSSession vs SQLSession for:

a) Speed.
b) Scalability.

Planned architecture employs multiple Zope/Apache 
frontline servers:

+-----+
| Z/A |---+
+-----+   |
          |
+-----+   |            
| Z/A |---+      +----- DB1 
+-----+   |      |
          |------|
+-----+   |      |
| Z/A |---+      +----- DB2 (optional)
+-----+   |
          |
          |
      Etc, etc.

Z/A = 'front line' webservers running Zope/Apache.
      Contains application/business logic. 
      We are NOT using the ZODB for data storage.

DB1 = Data storage. eg. Oracle/Postgres

DB2 = potentially just for managing the sessions, if
      we use SQLSession. Would MySQL be best ?


Just how scalable can it really get ? We need it to at least
be able to scale to 12 million sessions per day (and substant-
-ially more writes to DB1 per day), even if we will be starting
out much more modestly than that.  Realistically, should I be 
looking at something like ATG Dynamo instead ?  

Thank you very much,

chas