Subject: Re: [vserver] Shared Memory
From: Nikolay Kichukov <hijacker@oldum.net>
Date: Tue, 27 Oct 2009 09:52:21 +0200

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Hello,
you never specified kernel and util-vserver versions?

I am on 2.6.30.2-vs2.3.0.36.14-pre4 and ipcs returns correct results inside a guest.

Cheers,
- -Nik



Holger Amann wrote:
> 
> Am 27.10.2009 um 01:08 schrieb Holger Amann:
> 
>>
>> Am 27.10.2009 um 00:50 schrieb Timothee Besset:
>>
>>> I'm probably not familiar enough with how PostgreSQL works to help you,
>>> just going from my experience with Oracle here. I don't suppose pgsql's
>>> 'shared memory' could mean OS shared memory (as in, a tmpfs mount),
>>> because you have none. Oracle won't run if you're not giving it a
>>> /dev/shm tmpfs mount, but it's possible to do that for a guest (I do
>>> that). So all I can think of is that pgsql wants one and you haven't
>>> given any.
>>>
>>> TTimo
>>
>> Thank you for your help!
>>
>> I tried it (if the following is ok) and restarted Postgres, but it
>> made no difference in memory usage
>>
>> guest1:/var/log/postgresql# mount
>> /dev/hdv1 on / type ufs (defaults)
>> none on /proc type proc (defaults)
>> none on /tmp type tmpfs (size=16m,mode=1777)
>> none on /dev/pts type devpts (gid=5,mode=620)
>> tmpfs on /dev/shm type tmpfs (rw,size=4000M)
>>
>> Holger
> 
> 
> 
> I googled around and found an information [1], that Postgres does not
> use POSIX SHM. "PostgreSQL is using the old SYSV shared memory and
> semaphores, as evidenced
> by ipcs[...]"
> 
> So the output of ipcs on the guest is:
> 
> guest1:/dev/shm# ipcs
> 
> ------ Shared Memory Segments --------
> key        shmid      owner      perms      bytes      nattch     status
> 
> ------ Semaphore Arrays --------
> key        semid      owner      perms      nsems
> 
> ------ Message Queues --------
> key        msqid      owner      perms      used-bytes   messages
> 
> 
> and on a real machine:
> 
> postgrestest:~# ipcs
> 
> ------ Shared Memory Segments --------
> key        shmid      owner      perms      bytes      nattch     status
> 0x0052e2c1 65536      postgres  600        378953728  7
> 
> ------ Semaphore Arrays --------
> key        semid      owner      perms      nsems
> 0x0052e2c1 458752     postgres  600        17
> 0x0052e2c2 491521     postgres  600        17
> 0x0052e2c3 524290     postgres  600        17
> 0x0052e2c4 557059     postgres  600        17
> 0x0052e2c5 589828     postgres  600        17
> 0x0052e2c6 622597     postgres  600        17
> 0x0052e2c7 655366     postgres  600        17
> 
> ------ Message Queues --------
> key        msqid      owner      perms      used-bytes   messages
> 
> 
> So is it a Postgres specific problem, and/or could that be solved with
> Linux-Vserver?
> 
> [1] http://www.mail-archive.com/pgsql-bugs@postgresql.org/msg17969.html
> 
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