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Postgres shared memory error

From: Kevin Kempter <cs_dba(at)consistentstate(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Postgres shared memory error
Date: 2012-04-28 16:10:01
Message-ID: 4F9C1659.5070503@consistentstate.com (view raw or flat)
Thread:
Lists: pgsql-admin
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?

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?
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?

Thanks in advance



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Subject: Re: Postgres shared memory error
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