Re: FreeBSD: SMP and PostgreSQL

Mitch wrote:
> I've been playing with PG on a new FreeBSD 5.0 SMP box and I can't say
> the performance is dramatic, but I haven't done serious benchmarking
> yet. I will post the results if there is a gigantic leap..

> On Thursday, February 6, 2003, at 02:21 PM, Vivek Khera wrote:

>>>>>>>"RAD" == Ruslan A Dautkhanov <rusland(at)scn(dot)ru> writes:
>>RAD> Old releases (4.7, for example) also supports SMP, but worse
>>RAD> comparative with version 5 as described in above mentioned
>>RAD> release notes. Please say, if anybody test SMP in FreeBSD for
>>RAD> PostgreSQL - really Postgres with v5.0 will "dramatically"
>>RAD> increase SQL server performance?
>>
>>I run Postgres 7.2 on FreeBSD 4.7 with dual procs. Works fine. I
>>will wait until about FreeBSD 5.2 before I upgrade this server.

FreeBSD prior to 5.0 does not do SMP within a single process, i.e.
light-weight threads like SunOS/Solaris. However, this is almost
irrelevant with respect to PostgreSQL, since each connection to
PostgreSQL gets its own process. Thus, multi-CPUs on FreeBSD 4.x will
run the multiple PostgreSQL processes just in an SMP manner just fine.

Well, almost. SMP really means Symmetric Multi-Processing, not just
multiprocessors, and the FreeBSD 4.x kernel is not multi-threaded, so
during system calls, all processes are single threaded through the kernel.

FreeBSD 5.0 changes this and allows most, but not all, of the kernel to
be multi-threaded.

So to the extent that your performance is limited by kernel "bandwidth"
moving to FreeBSD 5.x will help. Chances are you'll be disk IO limited
long before you get kernel limited, though.