How can i see kernel patch version?

Hello experts.

How can i see kernel patch version? what are advantages applying that patch? 

Thanx in advance

The kernel patch revision is the one shown in uname -r.

The main advantage is bug fixes, but if your server(s) are stable there is no great rush to apply them. You should do it on a regular basis though, say once every quarter?

and DON'T use the kernel patch stand alone. always use the whole patch-cluster to satisfy all dependencies!

Thanx experts giving me good information.

Imagine I haven't applied any patch yet. What type of error messages will i get ? Is there any performance degradation ? How would i know whether apply or not?

No specific errors.. If might or might not get, depends, there's where patches are released.. Performance might or might not degrade depending on how your utilisation of the server is and what apps is running, and how system is maintained etc.. You can check the latest kernel patch release from sunsolve.sun.com

Thanx....