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Re: Postgres shared memory error

From: Kevin Kempter <cs_dba(at)consistentstate(dot)com>
To: Fernando Hevia <fhevia(at)gmail(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Postgres shared memory error
Date: 2012-04-28 16:37:58
Message-ID: 4F9C1CE6.20803@consistentstate.com (view raw or flat)
Thread:
Lists: pgsql-admin
On 04/28/2012 10:32 AM, Fernando Hevia wrote:
>
>
> On Sat, Apr 28, 2012 at 13:10, Kevin Kempter 
> <cs_dba(at)consistentstate(dot)com <mailto:cs_dba(at)consistentstate(dot)com>> wrote:
>
>     All;
>
>     I just want to be sure that I'm not causing myself greif.  I have
>     a kvm in the cloud that is supposed to have access to 32GB of ram.
>     when I do a top I only see 1GB of ram, I've pinged the hosting
>     provider, maybe it shows up as it's used?
>
>
> What does the 'free' command show?
>
>     Anyway when I try and start postgres I see this:
>     /
>      $ 2012-04-28 12:00:33 EDT [6429]: [1-1] FATAL:  XX000: could not
>     create shared memory segment: Cannot allocate memory
>     2012-04-28 12:00:33 EDT [6429]: [2-1] DETAIL:  Failed system call
>     was shmget(key=5432001, size=7700914176, 03600).
>     2012-04-28 12:00:33 EDT [6429]: [3-1] HINT:  This error usually
>     means that PostgreSQL's request for a shared memory segment
>     exceeded available memory or swap space. To reduce the request
>     size (currently 7700914176 bytes), reduce PostgreSQL's
>     shared_buffers parameter (currently 917504) and/or its
>     max_connections parameter (currently 503).
>             The PostgreSQL documentation contains more information
>     about shared memory configuration.
>     2012-04-28 12:00:33 EDT [6429]: [4-1] LOCATION: 
>     InternalIpcMemoryCreate, pg_shmem.c:178 /
>
>
>     Which means I should bump up shmmax like this:
>
>     /# sysctl -w kernel.shmmax=7700914176/
>
>
>     and add it to /etc/sysctl.conf:
>
>     /# tail /etc/sysctl.conf
>     kernel.msgmax = 65536
>
>     # Controls the maximum shared segment size, in bytes
>     kernel.shmmax = 68719476736
>
>     # Controls the maximum number of shared memory segments, in pages
>     kernel.shmall = 4294967296
>
>     #PostgreSQL
>     kernel.shmmax = 7700914176 /
>
>
>     I assume I should have to tweak ONLY kernel.shmmax, am I correct?
>
>
> Correct.
>
>     I'm also assuming that this is a KVM cloud host provider issue,
>     i.e. it looks like I actually do not have 32G or ram.  Does anyone
>     disagree with my conclusions?
>
>
> You haven't provided evidence on how much RAM your system sees. A free 
> -m will show the total memory the system has and is being used.
> Regards. 



Free command:

/ # free
              total       used       free     shared    buffers     cached
Mem:       1020856     946804      74052          0      61280     796004
-/+ buffers/cache:      89520     931336
Swap:            0          0          0/





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