Running large DB's on FreeBSD
Vivek Khera
vivek at khera.org
Mon Nov 13 19:18:44 UTC 2006
On Nov 10, 2006, at 6:35 PM, Nguyen Tam Chinh wrote:
>> For the pg configuration, I use this on a 4Gb box:
>>
>> max_connections = 100
>> shared_buffers = 70000 # min 16 or
>> max_connections*2, 8KB each
>> work_mem = 262144 # min 64, size in KB
>
> Thank you very much. And how did you set the semaphore's
> parameters? Do you have any trick or experience? I just think it's
> just weird to inceremently increase ipc.shm* and ipc.sem* to get
> the right values. The documentation of PostGreSQL gives us some
> examples but without explanation how they found those values.
The SEM parameters are the bare minimum. Pg uses a small number of
semaphores, so unless you have a bazillion connections allowed, just
use these settings:
kern.ipc.semmsl=512
kern.ipc.semmap=256
kern.ipc.semmni=32
kern.ipc.semmns=512
Now, for the SHM usage, it is just arithmetic. You now how many
buffers you're asking for, you know how big they are, and you just
need to add some for overhead and you've got your number. If you
want Pg to compute it for you, just read the error log when you fire
up Pg with a small shm setting in the OS.
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