Christopher Kings-Lynne wrote: > > Seriously, I know Linux can change these on the fly, and I'm pretty sure > > Solaris can too. I haven't played with BSD for a while so can't speak > > about that. Anyone else know? > > You cannot change SHMMAX on the fly on FreeBSD.
And part of the reason is because some/most BSD's map the page tables into physical RAM (kernel space) rather than use some shared page table mechanism. This is good because it prevents the shared memory from being swapped out (performance disaster). It doesn't actually allocate RAM unless someone needs it, but it does lock the shared memory into a specific fixed location for all processes. The more flexible approach is to make shared memory act just like the memory of a user process, and have other user processes share those page tables, but that adds extra overhead and can cause the memory to behave just like user memory (swapable). -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/users-lounge/docs/faq.html
