By my understanding, there is a limit to that.
Since there can be no more than 4GB memory addressed on a ix86 system
PER process (you can have 16 of these partitions of 4GB with a Xeon
machine) and the kernel allocates 1GB of memory for its own purposes
(can be adjusted up or down during the kernel compilation) it leaves you
with 3GB of memory maximum per process.
Ofcoarse it is possible that the sharedmemory handler has a max of 2GB
it is a "pretty number" ;)
What you should try first is whether you gain any performance from 1GB
to 1.5GB and from 1.5GB to 2GB...
If that doesn't improve any, why bother about the 3GB.
Martin Dillard wrote:
> We are trying to throw a lot of memory at PostgreSQL to try to boost
> performance. In an attempt to put our entire database into memory, I want to
> allocate 2 to 3 GB out of 4 GB on a dual processor server running Red Hat
> Linux 7.3 and PostgreSQL 7.2.1. We only expect 4 or 5 concurrent backends.
>
> When I try to allocate 2 GB or more, I get the following error when I try to
> start PostgreSQL (after setting kernel.shmall and kernel.shmmax
> appropriately):
>
> IpcMemoryCreate: shmat(id=163840) failed: Cannot allocate memory
>
> I can safely allocate a little under 2 GB. Is this a Linux upper bound on
> how much memory can be allocated to a single program? Is there another
> kernel parameter besides kernel.shmall and kernel.shmmax that can be set to
> allow more memory to be allocated?