Re: performance tuning: shared_buffers, sort_mem; swap

In article <27214.1029257785@sss.pgh.pa.us>,
 tgl@sss.pgh.pa.us (Tom Lane) wrote:

> Uh, which error exactly?  AFAIK all the shared-memory-related messages
> would only come out at postmaster startup, not during peak load.  The
> system is designed to ensure that those resources are all reserved
> during postmaster start.

Sorry, I should've included the whole error in the first place:

"IpcMemoryCreate: shmget(key=5432001, size=72368128, 03600) failed:
Invalid argument
This error usually means that PostgreSQL's request for a shared memory
segment exceeded your kernel's SHMMAX parameter. You can either reduce
the request size or reconfigure the kernel with larger SHMMAX. To reduce
the request size (currently 72368128 bytes), reduce PostgreSQL's
shared_buffers parameter (currently 8192) and/or its max_connections
parameter (currently 256). If the request size is already small, it's
possible that it is less than your kernel's SHMMIN parameter, in which
case raising the request size or reconfiguring SHMMIN is called for.

"The PostgreSQL Administrator's Guide contains more information about
shared memory configuration."

We've gotten this when the machine, a Red Hat 6.2 machine with kernel
2.4.17; Dual Pentium III 550 MHz processors; and 512 MB RAM is under
great duress.