SYSVSHM Kernel options

[Octavian Hornoiu]

I have been doing significant reading on the kernel options related to 
tuning PostgreSQL and I am wondering how to best go about increasing the 
paged memory available to FreeBSD.  I have read the following suggestions:

options         SYSVSHM
options         SHMMAXPGS=4096  (place total shared mem here)
options         SHMSEG=256
options         SYSVSEM
options         SEMMNI=256
options         SEMMNS=512
options         SEMMNU=256
options         SEMMAP=256
AND

/"You might also want to use the sysctl setting to lock shared memory 
into RAM and prevent it from being paged out to swap, e.g. 
kern.ipc.shm_use_phys"

/My question is, should i go ahead and increase the SHMMAXPGS value to 
any amount of memory that i choose?  what are the consequences of doing 
this on a freebsd system?  What problems might be caused and will this 
degrade the rest of the system?  What is the affect of locking shared 
memory into RAM using the sysctl utility?  I have never tuned the system 
in this way before and I am wary of messing around.

Thanks!

octavian

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