Originally posted by Halo
Originally posted by jm
Q:
I remember when I installed oracle, oratab will created by installer. if I install the 2nd version oracle, does oratab will be overwritten or skip it?
Not sure about this one.
The installer will append a second entry to the oratab file with the correct variables.
Q:
what's the easiest way to switch 2 versions?
I believe using . oraenv
I agree
Q:
I assue tnsname need modifying, how about listener, I should
use lower version or keep both?
You can keep both, they will be in their respective $O_H/network/admin
tnsnames.ora is the naming method for the client. The server only needs this information when connecting to another database or to itself via sql*net. I like to have one version of the tnsnames.ora file in the old $OH and create a link from the new $OH.

The listener.ora file is the configuration file for the listener. I would have one listener for the entire machine and have configure both databases for it. You should use the latest version of oracle installed for version the listener.
Q:
can I only update server, client still keep lower version?
can I mix (some clients use new verseion , some use old)
No problems here.