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Maximum value for SHMMAX

Is there a general rule concerning the maximum value to set SHMMAX to? I heard it should not be set to more than 75% of available RAM. Currently we are running two Oracle databases, have a total of 4 GB bytes of memory and have SHMMAX set to 1 GB byte. We are considering upping that to 3 GB bytes so that one of our databases can have more SGA.
I think setting SHMMAX to 75% of available memory is a little conservative. I like to set the SHMMAX to the size of the available memory (although I wouldn't actually make the SGA this big). This will give you the flexibility to increase the size of the SGA when you need to, without having to rebuild the kernel and reboot the UNIX machine.
This was last published in July 2002

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