swap space

[Chris Knipe]

>> We made the mistake however of just allocating 512MB swap as we did not
>> know accurately at the time of installation what the resouce requires are
>> going to be (especially not that it would be this high).
>
>  A traditional rule of thumb is to have 1x - 2x the total RAM size in
> swap space.  This assures that you can do a crash dump and that you can
> deal with peak load of 2x the normal maximum number of processes by
> swapping them out.  Beyond that, you are probably better off with the
> system just refusing to fork more processes or allocate them memory.

i.e. 4GB Ram, approx 8GB Swap?  In that case we'll need to install a 
secondary HDD in any case.  The current drive is already partitioned and 
what not, so reinstall isn't a option.  Having 2 or more swap partitions 
should also not be a big deal?  And this might be a extremely stupid 
question, but both are used at the same time right?

Some of our other high end perl systems use allot of memory as well.  We 
normally use stuff like SYSVSHM, SYSVMSG and SYSVSEM (Plus allot of 
parameters / options for it which I do not currently have with me 
unfortunately).  Me personally, are not 100% on what the drawbacks or 
benefits are, but would this make a difference?  In some of our production 
environments, we have applications terminating within seconds of reaching 
peak load without SYSV + "magic" options in the kernel.  This is not because 
of bad code, but because of severe load (thousands of concurrent 
connections). The server in question right now is basically a high end 
anti-spam / anti-virus solution (which by nature is extremely resource 
intensive - look at big SA installations for example).

We are already running with MAXUSERS 512 and NMBCLUSTERS=65535 as "advanced" 
features in the kernel currently.  I suppose I should recompile and add SYSV 
(after I got the "magic" options again).  Those two options are also so far 
the only options I found to "tune" for a high performance FBSD config... If 
anyone have additional resources, please feel free to share... :)

I'm talking under correction, but I believe the "magic" options to the SYSV 
stuff is related to specifying the ammounts of ram to use, etc.

Thanks for all the answers and suggestions!!!

--
Chris.