Hi,

i wants to increase the Ram from 1GB to 8GB in my Linux machine..

I use CentOS5.5 version el5 destro....
i have a doubt that if i increase the "Ram" to 8GB should i want to increase the "Swap" space also...

please suggest me on this.....

This is a somewhat debated topic..
The short answer is, take into consideration what your server is doing, and what loads it is/will be under with respect to RAM.
Do you expect that you will often max out your physical RAM? And if so, how much by.. Your swap should be this, plus a bit for good measure. (This does not apply for laptops with hibernation and what not.) Keep in mind, that the more RAM you have, the less you will need to swap.

Other than that, a google search will turn up lots of debating on the subject.
http://lmgtfy.com/?q=linux+swap+size

Also keep in mind, you will probably need to use a 64bit or PAE kernel, if you aren't already.

Thanks, for your reply, can i able increase RAM 8GB in 32bit Operating system ,we use

Redhat5.

With a stock 32bit kernel, no.
Google turned up some results for running a PAE kernel with centos 5/rhel5..
Or you can upgrade to 64bit, assuming your hardware can support it.. If it is a 32bit CPU then the hardware may not support 8G RAM anyway..

How will the workload change after the ram increase?

If you plan to run the same workload (increasing ram just to make that workload run faster) then the increase in ram decreases the need for swap. (For swap size decisions, doing more work sequentially, because the system is faster, is not a higher workload. Only doing more work simultaneously is a higher workload).

If you plan to increase the workload (run more simultaneously or larger of whatever services or applications are running) when you increase the amount of ram, then that may call for an increase in swap as well.

If your hardware supports 8GB, then a Centos 32bit PAE kernel supports 8GB.
If you have a non PAE kernel in 32 bit Centos, it is easy to switch to a PAE kernel (install the package and reboot). It is much harder to switch to a 64 bit kernel. A 64 bit kernel might be better or worse for your purposes than PAE (better is more likely, but it is hard to predict). 64bit is not likely to be enough better to be worth the extra trouble of switching.