Re: [GENERAL] Preventing OOM kills
On 05/25/2011 03:01 AM, John R Pierce wrote: On 05/24/11 5:50 PM, Andrej wrote: Add more RAM? Look at tunables for other processes on the machine? At the end of the day making the kernel shoot anything out of despair shouldn't be the done thing. somehow, 'real' unix has neither a OOMkiller nor does it flat out die under heavy loads, it just degrades gracefully. I've seen Solaris and AIX and BSD servers happily chugging along with load factors in the 100s, significant portions of memory paging, etc, without completely crumbling to a halt. Soimetimes I wonder why Linux even pretends to support virtual memory, as you sure don't want it to be paging. http://developers.sun.com/solaris/articles/subprocess/subprocess.html Some operating systems (such as Linux, IBM AIX, and HP-UX) have a feature called memory overcommit (also known as lazy swap allocation). In a memory overcommit mode, malloc() does not reserve swap space and always returns a non-NULL pointer, regardless of whether there is enough VM on the system to support it or not. The memory overcommit feature has advantages and disadvantages. (the page goes on with some interesting info) [*] It appears by your definition that neither Linux, AIX nor HP-UX are 'real' Unix. Oh, wait, FreeBSD overcommits, too, so can't be 'real' either. /me wonders now what a 'real' Unix is. :) Must be something related with 'true' SysV derivatives. If memory serves me well, that's where the word 'thrashing' originated, right? Actually in my experience nothing 'thrashes' better than a SysV, Solaris included. The solution for the OP problem is to keep the system from reaching OOM state in the first place. That is necessary even with overcommitting turned off. PG not performing its job because malloc() keeps failing isn't really a solution. .TM. [*] One missing piece is that overcommitting actually prevents or delays OOM state. The article does mention system memory can be used more flexibly and efficiently w/o really elaborating further. It means that, given the same amount of memory (RAM+swap), a non overcommitting system reaches OOM way before than a overcommitting one. Also it is rarely a good idea, when running low on memory, to switch to an allocation policy that is _less_ efficient, memory wise. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
[GENERAL] Preventing OOM kills
PG tends to be picked on by the Linux OOM killer, so lately we've been forcing the OOM killer to kill other processes first with this script: while true; do for i in `pgrep postgres`; do echo -17 /proc/$i/oom_adj done sleep 60 done Is there a Better Way? Thanks in advance. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Preventing OOM kills
On 25 May 2011 12:32, Yang Zhang yanghates...@gmail.com wrote: PG tends to be picked on by the Linux OOM killer, so lately we've been forcing the OOM killer to kill other processes first with this script: while true; do for i in `pgrep postgres`; do echo -17 /proc/$i/oom_adj done sleep 60 done Is there a Better Way? Thanks in advance. Add more RAM? Look at tunables for other processes on the machine? At the end of the day making the kernel shoot anything out of despair shouldn't be the done thing. Cheers, Andrej -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Preventing OOM kills
On Tue, May 24, 2011 at 6:50 PM, Andrej andrej.gro...@gmail.com wrote: On 25 May 2011 12:32, Yang Zhang yanghates...@gmail.com wrote: PG tends to be picked on by the Linux OOM killer, so lately we've been forcing the OOM killer to kill other processes first with this script: while true; do for i in `pgrep postgres`; do echo -17 /proc/$i/oom_adj done sleep 60 done Is there a Better Way? Thanks in advance. Add more RAM? Look at tunables for other processes on the machine? At the end of the day making the kernel shoot anything out of despair shouldn't be the done thing. I thought that setting vm.overcommit_memory=2 stopped the OOM killer. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Preventing OOM kills
On Tue, 2011-05-24 at 17:32 -0700, Yang Zhang wrote:
PG tends to be picked on by the Linux OOM killer, so lately we've been
forcing the OOM killer to kill other processes first with this script:
while true; do
for i in `pgrep postgres`; do
echo -17 /proc/$i/oom_adj
done
sleep 60
done
Is there a Better Way? Thanks in advance.
Why don't you start postmaster with this value? Here is what we do in
RPM init scripts.
PG_OOM_ADJ=-17
test x$PG_OOM_ADJ != x echo $PG_OOM_ADJ /proc/self/oom_adj
$SU -l postgres -c $PGENGINE/postmaster -p '$PGPORT' -D '$PGDATA'
${PGOPTS} $PGLOG 21 /dev/null
Regards,
--
Devrim GÜNDÜZ
Principal Systems Engineer @ EnterpriseDB: http://www.enterprisedb.com
PostgreSQL Danışmanı/Consultant, Red Hat Certified Engineer
Community: devrim~PostgreSQL.org, devrim.gunduz~linux.org.tr
http://www.gunduz.org Twitter: http://twitter.com/devrimgunduz
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Re: [GENERAL] Preventing OOM kills
On 05/24/11 5:50 PM, Andrej wrote: Add more RAM? Look at tunables for other processes on the machine? At the end of the day making the kernel shoot anything out of despair shouldn't be the done thing. somehow, 'real' unix has neither a OOMkiller nor does it flat out die under heavy loads, it just degrades gracefully. I've seen Solaris and AIX and BSD servers happily chugging along with load factors in the 100s, significant portions of memory paging, etc, without completely crumbling to a halt.Soimetimes I wonder why Linux even pretends to support virtual memory, as you sure don't want it to be paging. -- john r pierceN 37, W 123 santa cruz ca mid-left coast -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Preventing OOM kills
On Tue, May 24, 2011 at 7:01 PM, John R Pierce pie...@hogranch.com wrote: On 05/24/11 5:50 PM, Andrej wrote: Add more RAM? Look at tunables for other processes on the machine? At the end of the day making the kernel shoot anything out of despair shouldn't be the done thing. somehow, 'real' unix has neither a OOMkiller nor does it flat out die under heavy loads, it just degrades gracefully. I've seen Solaris and AIX and BSD servers happily chugging along with load factors in the 100s, significant portions of memory paging, etc, without completely crumbling to a halt. Soimetimes I wonder why Linux even pretends to support virtual memory, as you sure don't want it to be paging. I've found that on servers with multiple drives and the page file spread across them linux does pretty well when swapping out. Even going pretty far back, when I had 6 9G SCSI drives on an old Sparc 20 running RHEL with 256M ram the swapping was quite speedy with a 100M or so on each drive. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
