Re: Postgres shared memory error

On Sat, Apr 28, 2012 at 13:10, Kevin Kempter <cs_dba@consistentstate.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.