It seems I don't fully understand the bigmem situation. I've searched the archives, googled, checked RedHat's docs, etc. But I'm getting conflicting, incomplete and/or out of date information. Does anyone have pointers to bigmem info or configuration for the 2.4 kernel?
Bigmem is the name for Linux's PAE support.
If Linux is setup with 2GB for kernel and 2GB for user, would that be OK with a DB size of 2-2.5 GB? I'm figuring the kernel will cache most/all of the DB in it's 2GB and there's 2GB left for PG processes. Where does PG's SHM buffers live, kernel or user? (I don't plan on going crazy with buffers, but will guess we'd need about 128MB, 256MB at most.)
PG's SHM buffers live in user. Whether Linux's OS caches lives in user or kernel, I think it's in kernel and I remember reading a max of ~950KB w/o bigmem which means your 3.5GB of available OS memory will definitely have to be swapped in and out of kernel space using PAE.
Well if this is the case, you probably should get an Opteron server *now* and just run 32-bit Linux on it until you're sure about the software. No point in buying a Xeon and then throwing the machine away in a year when you decide you need 64-bit for more speed.
That's a good point. I had forgotten about the option to run 32bit on an Operton. If we had 3GB or 4GB initially on an Opteron, we'd need bigmem for 32bit Linux, right?
This might work nicely since we'd factor in the penalty from PAE for now and have the performance boost from moving to 64bit available on demand. Not having to build another DB server in a year would also be nice.
FYI, we need stability first and performance second.
We ordered a 2x Opteron server the moment the CPU was released and it's been perfect -- except for one incident where the PCI riser card had drifted out of the PCI slot due to the heavy SCSI cables connected to the card.
I think most of the Opteron server MBs are pretty solid but you want extra peace-of-mind, you could get a server from Newisys as they pack in a cartload of extra monitoring features.
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