Gavin Sherry wrote:
> There is no problem with free Linux distros handling > 4 GB of memory. The
> problem is that 32 hardware must make use of some less than efficient
> mechanisms to be able to address the memory.
The theshold for using PAE is actually far lower than 4GB. 4GB is the
total memory address space -- split that in half for 2GB for userspace,
2GB for kernel. The OS cache resides in kernel space -- after you take
alway the memory allocation for devices, you're left with a window of
roughly 900MB.
Since the optimal state is to allocate a small amount of memory to
Postgres and leave a huge chunk to the OS cache, this means you are
already hitting the PAE penalty at 1.5GB of memory.