[CentOS] change /etc/security/limits.conf need reboot or not?

Wed Mar 20 18:52:10 UTC 2013
mcclnx mcc <mcclnx at yahoo.com.tw>

We have CEntos 5.5 on DELL server.  Due to more and more databases run on same server sometime processes number read max and cause 'resource temporary unavailable".

I plan to change /etc/security/limits.conf value:

oracle          soft    nproc          2047 ==> 4096

Do i need reboot to make it effect?

How to test change is effect?

Thanks.