Christian Bucanac <christian.bucanac@mindark.com> writes:
>> I am going to try 768M (98304) for buffers and 6144 (6144 * 32 = 192M)
>> for sort mem. This way with the DB server serving a max of 32 application
>> servers the kernel and other processes should still have the last 64Mb RAM.
This is almost certainly a lousy idea. You do *not* want to chew up all
available memory for PG shared buffers; you should leave a good deal of
space for kernel-level disk buffers.
Other fallacies in the above: (1) you're assuming the SortMem parameter
applies once per backend, which is not the case (it's once per sort or
hash step in a query, which could be many times per backend); (2) you're
not allowing *anything* for any space usage other than shared disk
buffers and sort memory.
The rule of thumb I recommend is to use (at most) a quarter of real RAM
for shared disk buffers. I don't have hard measurements to back that
up, but I think it's a lot more reasonable as a starting point than
three-quarters of RAM.
regards, tom lane
