Hello! 

> Thank you very much. I didn't know that. I set my shmmax to 4000000000 but 
> you're right, we will see to use a 64 bits system ;) 

My experience with this amount of memory in Debian Etch works much better in a 
64bit environment. BIGMEM kernel handles pages in a way that the performance is 
a bit degraded. 

> I wanted to give to postgres 4GB. So I tryied to set shmmax to 4Go :
>
>     sysctl kernel.shmmax=4294967296
>
>
> But it doesn't work : if I launch after this modification this command :
>
>     sysctl kernel.shmmax
>
> it gives me this response :
>
>     kernel.shmmax = 0
>
> Why? Is there a limit to shmmax? 

I don't see limits in shmmax but the command you're typing is wrong. 
To set a value you need to do: 
sysctl -w kernel.shmmax=VALUE 

or alternatively: 
cat VALUE > /proc/sys/kernel/shmmax 

Don't forget to write in your /etc/sysctl.conf: 
kernel.shmmax=VALUE 
Without spaces. This will make your setting persistent. 

Regards 
Flavio 

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