Re: Postgres not using shared memory

Karl O. Pinc wrote:

> Hi,
>
> I can't seem to get postgresql to use shared memory and performance is
> terrrible.
>
>  PostgreSQL 7.4.6 on i686-redhat-linux-gnu, compiled by GCC gcc (GCC)
> 3.2.3 20030502 (Red Hat Linux 3.2.3-42)
>
> $ uname -a
> Linux artsdata 2.4.21-20.0.1.ELsmp #1 SMP Wed Nov 24 20:34:01 EST 2004
> i686 i686 i386 GNU/Linux
>
> $ free
>              total       used       free     shared    buffers     cached
> Mem:       2055336    1614408     440928          0       4240    1488104
> -/+ buffers/cache:     122064    1933272
> Swap:      2096440       1216    2095224
>
> $ /sbin/sysctl -a | grep shm
> ...
> kernel.shmall = 1073741823
> kernel.shmmax = 1073741823


free will not correctly show shared memory usage if you are allocating
more than
512 megs (I think). I don't recall the exact amount but this is a
limitation of free.

What type of hard drives do you have? What does a sar 1 or iostat report?

Sincerely,

Joshua D. Drake


> (I had both above 1 larger, and tried cutting it down by one out of
> endpoint paranoia.  That should be 1GB.)
>
> postgresql.conf:
> #shared_buffers = 126976         # 1GB - 32MB (just to leave some
> below kernel limit)
> shared_buffers = 6000 # testing to get _some_ shared memory
>
> => select * from pg_settings where name = 'shared_buffers';
>       name      | setting |  context   | vartype |       source
> | min_val |  max_val
> ----------------+---------+------------+---------+--------------------+---------+------------
>
>  shared_buffers | 6000    | postmaster | integer | configuration file
> | 16      | 2147483647
> (1 row)
>
> I've see my setting in pg_settings all along, but free never shows me
> any shared
> memory used.
>
> I've tried shutting down all the other daemons and restarting
> postgresql and nothing
> changes.
>
> What am I doing wrong here?
>
> Thanks.
>
> Karl <kop@meme.com>
> Free Software:  "You don't pay back, you pay forward."
>                  -- Robert A. Heinlein
>
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