lightweight user switching

Anyone knows how costly is the so called "lightweight user switch" or
"lightweight user sessions within a single database session" (see
"Oracle Call Interface Programmer's Guide", chapter "Middle-Tier
Applications in OCI")

In short this process [re]authenticates a new user on the same
"connection" (which creates a new v$session entry with new user name,
sid, serial#, audsid) but keeps the same v$process.spid

As far as I guess this method is used for Oracle's Apache mod_plsql module.

Thank you in advance,
Laimis N.
Fyrirvari/Disclaimer
http://www.landsbanki.is/disclaimer

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