postgresql and smp linux kernel

Started by zhicheng wangover 21 years ago7 messagesgeneral

wang_zc@yahoo.co.uk

over 21 years ago

Dear all

i have a dedicated server mainly running postgresql,
currently rh-posgtresql-7.3.6.7 (and samba, ypbind
etc). The server is a dual processor machine and the
OS is RHEL AS 3.

I am currently running kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel for
postgresql? What is benefit of it? If I run UP kernel,
what do I lose from the point view of PG?

Thanks

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com

Oliver Elphick

olly@lfix.co.uk

over 21 years ago

In reply to: zhicheng wang (#1)

Re: postgresql and smp linux kernel

On Mon, 2004-08-09 at 11:10, zhicheng wang wrote:

Dear all

i have a dedicated server mainly running postgresql,
currently rh-posgtresql-7.3.6.7 (and samba, ypbind
etc). The server is a dual processor machine and the
OS is RHEL AS 3.

I am currently running kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel for
postgresql? What is benefit of it? If I run UP kernel,
what do I lose from the point view of PG?

You do not NEED it for Pg, but it will improve performance. Each
separate session gets a different process and therefore has a change to
run on the second processor concurrently with another session on the
first processor. The same goes for any other processes that are
running, of course.

If you do not use an SMP kernel, one of your processors will sit there
for ever doing nothing, which is money down the drain.

--
Oliver Elphick olly@lfix.co.uk
Isle of Wight http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E 1EC0 5664 7A2F A543 10EA
========================================
"Be still before the LORD and wait patiently for him;
do not fret when men succeed in their ways, when they
carry out their wicked schemes."
Psalms 37:7

zhicheng wang

wang_zc@yahoo.co.uk

over 21 years ago

In reply to: Oliver Elphick (#2)

Re: postgresql and smp linux kernel

Thanks Oliver Elphick
does this mean that the applications do not need to be
multi-threading in order to use multi-processors?

cheng

 --- Oliver Elphick <olly@lfix.co.uk> wrote:

On Mon, 2004-08-09 at 11:10, zhicheng wang wrote:

Dear all

i have a dedicated server mainly running

postgresql,

currently rh-posgtresql-7.3.6.7 (and samba, ypbind
etc). The server is a dual processor machine and

the

OS is RHEL AS 3.

I am currently running

kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel for
postgresql? What is benefit of it? If I run UP

kernel,

what do I lose from the point view of PG?

You do not NEED it for Pg, but it will improve
performance. Each
separate session gets a different process and
therefore has a change to
run on the second processor concurrently with
another session on the
first processor. The same goes for any other
processes that are
running, of course.

If you do not use an SMP kernel, one of your
processors will sit there
for ever doing nothing, which is money down the
drain.

--
Oliver Elphick
olly@lfix.co.uk
Isle of Wight
http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E 1EC0
5664 7A2F A543 10EA

========================================
"Be still before the LORD and wait patiently
for him;
do not fret when men succeed in their ways,
when they
carry out their wicked schemes."
Psalms 37:7

---------------------------(end of
broadcast)---------------------------
TIP 5: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faqs/FAQ.html

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com

Import Notes

Reply to msg id not found: 10549538.1092048895492.JavaMail.root@hercules | Resolved by subject fallback

Bill Moran

wmoran@potentialtech.com

over 21 years ago

In reply to: zhicheng wang (#3)

Re: postgresql and smp linux kernel

zhicheng wang <wang_zc@yahoo.co.uk> wrote:

Thanks Oliver Elphick
does this mean that the applications do not need to be
multi-threading in order to use multi-processors?

Yes, that's what it means. Although you've probably oversimplified it
too much. Multi-process applications make use of multiple processors
just as well as multi-threaded apps do.

--- Oliver Elphick <olly@lfix.co.uk> wrote: 
On Mon, 2004-08-09 at 11:10, zhicheng wang wrote:

Dear all

i have a dedicated server mainly running

postgresql,

currently rh-posgtresql-7.3.6.7 (and samba, ypbind
etc). The server is a dual processor machine and

the

OS is RHEL AS 3.

I am currently running

kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel for
postgresql? What is benefit of it? If I run UP

kernel,

what do I lose from the point view of PG?

You do not NEED it for Pg, but it will improve
performance. Each
separate session gets a different process and
therefore has a change to
run on the second processor concurrently with
another session on the
first processor. The same goes for any other
processes that are
running, of course.

If you do not use an SMP kernel, one of your
processors will sit there
for ever doing nothing, which is money down the
drain.

--
Oliver Elphick
olly@lfix.co.uk
Isle of Wight
http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E 1EC0
5664 7A2F A543 10EA

========================================
"Be still before the LORD and wait patiently
for him;
do not fret when men succeed in their ways,
when they
carry out their wicked schemes."
Psalms 37:7

---------------------------(end of
broadcast)---------------------------
TIP 5: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faqs/FAQ.html

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com

---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster

--
Bill Moran
Potential Technologies
http://www.potentialtech.com

Scott Marlowe

smarlowe@qwest.net

over 21 years ago

In reply to: zhicheng wang (#1)

Re: postgresql and smp linux kernel

On Mon, 2004-08-09 at 04:10, zhicheng wang wrote:

Dear all

i have a dedicated server mainly running postgresql,
currently rh-posgtresql-7.3.6.7 (and samba, ypbind
etc). The server is a dual processor machine and the
OS is RHEL AS 3.

I am currently running kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel for
postgresql? What is benefit of it? If I run UP kernel,
what do I lose from the point view of PG?

Let's be clear here, PostgreSQL isn't responsible for exploiting your
second CPU, the OS is. The face that PostgreSQL spawns a new backend
process for each connection means that it can use about as many
processors as it has connections, plus maybe one for the OS.

However, the OS will not schedule anything to run at all on the second
CPU if you run a UP kernel.

Generally, the linux and bsd kernels both tend to get a scaling factor
of near unity for the second CPU with enough things to do in parallel.
There's almost no loss for single processes hogging one CPU, and even
these tasks are often sped up by the OS having a CPU to run on while
your one big process is hogging the other one.

Considering you're running samba, which is also process based, it would
be wise to enable the second CPU in the kernel, otherwise pull it, put
in the terminator, and save it in case of future CPU failure. It won't
be doing you any good.

zhicheng wang

wang_zc@yahoo.co.uk

over 21 years ago

In reply to: Scott Marlowe (#5)

Re: postgresql and smp linux kernel

Thanks for the clear answer.

What about hyper-threading? At the moment, I have
hyper-threading enabled and the OS sees four CPUs (two
physical and two virtual). Do these two virtual ones
really work as the real ones?

I am asking these because we use SAN disks and the
secure-path (a fail safe mechanism) only support UP
kernel. I have to choose do we run smp or do we make
use of secure-path.

Regards
cheng

 --- Bill Moran <wmoran@potentialtech.com> wrote:

zhicheng wang <wang_zc@yahoo.co.uk> wrote:

Thanks Oliver Elphick
does this mean that the applications do not need

to be

multi-threading in order to use multi-processors?

Yes, that's what it means. Although you've probably
oversimplified it
too much. Multi-process applications make use of
multiple processors
just as well as multi-threaded apps do.
--- Oliver Elphick <olly@lfix.co.uk> wrote: 
On Mon, 2004-08-09 at 11:10, zhicheng wang
wrote:

Dear all

i have a dedicated server mainly running

postgresql,

currently rh-posgtresql-7.3.6.7 (and samba,

ypbind

etc). The server is a dual processor machine

and

the

OS is RHEL AS 3.

I am currently running

kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel

for

postgresql? What is benefit of it? If I run UP

kernel,

what do I lose from the point view of PG?

You do not NEED it for Pg, but it will improve
performance. Each
separate session gets a different process and
therefore has a change to
run on the second processor concurrently with
another session on the
first processor. The same goes for any other
processes that are
running, of course.

If you do not use an SMP kernel, one of your
processors will sit there
for ever doing nothing, which is money down the
drain.

--
Oliver Elphick

olly@lfix.co.uk
Isle of Wight
http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E

1EC0

5664 7A2F A543 10EA

========================================
"Be still before the LORD and wait

patiently

for him;
do not fret when men succeed in their

ways,

when they
carry out their wicked schemes."
Psalms 37:7

---------------------------(end of
broadcast)---------------------------
TIP 5: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faqs/FAQ.html

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW

Yahoo! Messenger - all new features - even more fun!
http://uk.messenger.yahoo.com

---------------------------(end of

broadcast)---------------------------

TIP 4: Don't 'kill -9' the postmaster

--
Bill Moran
Potential Technologies
http://www.potentialtech.com

---------------------------(end of
broadcast)---------------------------
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cleanly

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com

Import Notes

Reply to msg id not found: 21122387.1092055191915.JavaMail.root@hercules | Resolved by subject fallback

Bill Moran

wmoran@potentialtech.com

over 21 years ago

In reply to: zhicheng wang (#6)

Re: postgresql and smp linux kernel

zhicheng wang <wang_zc@yahoo.co.uk> wrote:

Thanks for the clear answer.

What about hyper-threading? At the moment, I have
hyper-threading enabled and the OS sees four CPUs (two
physical and two virtual). Do these two virtual ones
really work as the real ones?

This question really belongs on the list for the OS you're using. It's
much more dependent on the OS than PostgreSQL.

However, if you're using FreeBSD 5, I can say from experience that
PostgreSQL makes full use of hyperthreaded processors when running on
FreeBSD 5.

If you're not running FreeBSD 5, someone else will have to answer.

I am asking these because we use SAN disks and the
secure-path (a fail safe mechanism) only support UP
kernel. I have to choose do we run smp or do we make
use of secure-path.

Regards
cheng
--- Bill Moran <wmoran@potentialtech.com> wrote: 
zhicheng wang <wang_zc@yahoo.co.uk> wrote:

Thanks Oliver Elphick
does this mean that the applications do not need

to be

multi-threading in order to use multi-processors?

Yes, that's what it means. Although you've probably
oversimplified it
too much. Multi-process applications make use of
multiple processors
just as well as multi-threaded apps do.
--- Oliver Elphick <olly@lfix.co.uk> wrote: 
On Mon, 2004-08-09 at 11:10, zhicheng wang
wrote:

Dear all

i have a dedicated server mainly running

postgresql,

currently rh-posgtresql-7.3.6.7 (and samba,

ypbind

etc). The server is a dual processor machine

and

the

OS is RHEL AS 3.

I am currently running

kernel-smp-2.4.21-15.0.4.EL.

My question is: do i need to run smp kernel

for

postgresql? What is benefit of it? If I run UP

kernel,

what do I lose from the point view of PG?

You do not NEED it for Pg, but it will improve
performance. Each
separate session gets a different process and
therefore has a change to
run on the second processor concurrently with
another session on the
first processor. The same goes for any other
processes that are
running, of course.

If you do not use an SMP kernel, one of your
processors will sit there
for ever doing nothing, which is money down the
drain.

--
Oliver Elphick

olly@lfix.co.uk
Isle of Wight
http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E

1EC0

5664 7A2F A543 10EA

========================================
"Be still before the LORD and wait

patiently

for him;
do not fret when men succeed in their

ways,

when they
carry out their wicked schemes."
Psalms 37:7

---------------------------(end of
broadcast)---------------------------
TIP 5: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faqs/FAQ.html

=====
Best wishes
Z C Wang
___________________________________________________________ALL-NEW

Yahoo! Messenger - all new features - even more fun!
http://uk.messenger.yahoo.com

---------------------------(end of

broadcast)---------------------------

TIP 4: Don't 'kill -9' the postmaster

--
Bill Moran
Potential Technologies
http://www.potentialtech.com

---------------------------(end of
broadcast)---------------------------
TIP 3: if posting/reading through Usenet, please
send an appropriate
subscribe-nomail command to
majordomo@postgresql.org so that your
message can get through to the mailing list
cleanly

=====
Best wishes
Z C Wang

___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com

---------------------------(end of broadcast)---------------------------
TIP 3: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to majordomo@postgresql.org so that your
message can get through to the mailing list cleanly

--
Bill Moran
Potential Technologies
http://www.potentialtech.com