Re: Questions about tuning on FreeBSD... - Mailing list pgsql-general

What about WAL buffer parameter ?

i thought if this buffer is too small, un necessary I/O will occur and slow
down performance

<postgres@vsservices.com> wrote in message
news:01091023443406.73075@prime.vsservices.com...
> On Monday 10 September 2001 18:52, Philip Hallstrom wrote:
> > Hi all -
> > I have some questions about tuning the various kernel parameters
> > on FreeBSD.  I've read Bruce's article a couple of times and the various
> > parts of the documentation, but I still have some questions and was
hoping
> > people here could confirm/deny my assumptions.
> >
> > The machine in question has 512 megs of ram and doesn't do anything else
> > significant other than postgresql.
> >
> Depending on the size of your DB, this should do OK...
>
> > As I understand there are two major tuneable parameters:
> >
> > - shared buffer cache: which I can think of as a sort of RAM-based
> > disk cache of recently accessed tables (or parts of tables).  Ideally
this
> > would be large enough to hold the entire database.  The goal is to make
> > this large enough to hold the most commonly accessed tables.
> I run with shared buffers = 5120
>
> > - sort memory batch size: this is the amount of memory that *each
backend*
> > uses to do it's sorts/merges/joins.  If the backend needs more than this
> > then it writes to temporary files.  Again the goal would be to make all
> > your sorts/merges/joins fit in this size.
>
> Sort Mem = 4096
>
> > The overall goal is to give enough memory to postgresql so that it
writes
> > to disk as little as possible while making sure that the OS as a whole
> > doesn't have to start swapping.  So as a starting point could one
install
> > the OS, let it run for a bit, see how much memory it's using, see how
much
> > memory is left and assign most of that to postgresql?
> >
> >
> > Regarding the KERNEL parameters.  I can follow the general rules
mentioned
> > in the docs for configuring things no problem.  However is there any
> > danger in doing that?  Can they be too big?  Or can they only be too big
> > in conjunction with giving postgresql too much memory?  In otherwords if
I
> > set them to something, but don't run postgresql have I affected how the
OS
> > will run by itself?
> >
> > Is there a way to determine the maximum number of backends that can be
run
> > given a given amount of RAM?
> >
> > Also, if anyone has a Free# SYSV stuff BSD box with 512 ram, what are
your
> > kernel settings?
>
> options         SYSVSHM                 #SYSV-style shared memory
> options         SHMMAXPGS=12288
> options         SHMMAX="(SHMMAXPGS*PAGE_SIZE+1)"
> options         SHMSEG=256
> options         SHMMNI=512
> options         SHMMIN=1
>
> options         SYSVMSG                 #SYSV-style message queues
>
> options         SYSVSEM                 #SYSV-style semaphores
> options         SEMMNI=256
> options         SEMMNS=512
> options         SEMMNU=256
> options         SEMMAP=256
>
> Note:  Some of these might be WAY TOO high!
> I could not find enough docs to tell me, so I just added extra
> everywhere....  Maybe some of the experts can pick this apart...
>
> >
> > Thanks!
> >
> > -philip
> >
> >
> On that note:  Could some of the PostgreSQL expert take a look my
> number of buffers and the kernel config and tell me if I'm running too
> much of anything?
>
> GB
>
> --
> GB Clark II             | Roaming FreeBSD Admin
> gclarkii@VSServices.COM | General Geek
>            CTHULU for President - Why choose the lesser of two evils?
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster