shared_buffer setting

On 10/6/06, km <km@mrna.tn.nic.in> wrote:

Hi all,
Iam using postgresql 8.1.4 with 8GB physical RAM.

OS kernel max shared memory usage is set to( /proc/sys/kernel/shmmax)
33554432
dont know if this number is in bytes or bits
now how do i set my shared_buffer setting in postgresql.conf such that
ican use max shared memory setting of the kernel.

also default shared_buffer setting is 1000 - its not clear if i have to
multiply this number with 8KB to be <= max shared memory value or it is 1000
bytes or bits.
can i set the max shared memory value to use atleast half of my physicl
RAM available ?
any idea ?
also i would like to know how is the performance hit when we change
shared_buffer value in general ?

regards,
KM

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On 10/6/06, Talha Khan <talha.amjad@gmail.com> wrote:

Hi Km,

The shmmax setting is in bits.

For knowing the details about the shared_buffer settings and
other configuration features follow the link given below:

http://www.powerpostgresql.com/PerfList

The shmmax value set in your kernel (i.e 33554432) seems quite low seeng
that you have 8GB physical RAM. Yes! you can set shmmax to half of your RAM
but it all depends upon how you use your system .I would recommend setting
it to 2/3 of your RAM.You can set the value in sysctl.conf file. and then
reflect the setting by using sysctl -p switch.

Regards
Talha Khan

On 10/6/06, km <km@mrna.tn.nic.in> wrote:

Hi all,
Iam using postgresql 8.1.4 with 8GB physical RAM.

OS kernel max shared memory usage is set to( /proc/sys/kernel/shmmax)
33554432
dont know if this number is in bytes or bits
now how do i set my shared_buffer setting in postgresql.conf such that
ican use max shared memory setting of the kernel.

also default shared_buffer setting is 1000 - its not clear if i have to
multiply this number with 8KB to be <= max shared memory value or it is 1000
bytes or bits.
can i set the max shared memory value to use atleast half of my physicl
RAM available ?
any idea ?
also i would like to know how is the performance hit when we change
shared_buffer value in general ?

regards,
KM

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