Обсуждение: PG 8.1.1 Cannot allocate shared_buffers memory error

I just installed postgres 8.1.1 on a dual optron Linux box running Linux
4 advanced server, with 32GB of RAM and 2GB of swap.
I'm trying to allocate 24 GB as shared_bufferes. I'm getting an error
that I can not allocate memory (see below). If I change my
shared_buffers to 16GB, postgres starts up with no issue. I'm trying to
understand why I'm getting the shared memory error at sizes above 16GB
whilst I have 32GB with appropriate (I think) settings of kernel
parameters. Any help is appreciated. Thanks...

My sysctl.conf has :
  kernel.shmmax = 34359738368
  kernel.shmall = 34359738368   (32GB).

And here's some of related postgresql.conf parameters:

  shared_buffers = 2359296
  work_mem = 16384
  maintenance_work_mem = 2097152
  max_connections = 100
  effective_cache_size = 2621440

---
Error:

 FATAL:  could not create shared memory segment: Cannot allocate memory
[2005-12-14 13:56:03 PST|||] DETAIL:  Failed system call was
shmget(key=5432001, size=19760111616, 03600).
[2005-12-14 13:56:03 PST|||] 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 19760111616
bytes), reduce PostgreSQL's shared_buffers parameter (currently 2359296)
and/or its max_connections parameter (currently 100).

---

Regards,

  Husam Tomeh

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"Tomeh, Husam" <htomeh@firstam.com> writes:
> I just installed postgres 8.1.1 on a dual optron Linux box running Linux
> 4 advanced server, with 32GB of RAM and 2GB of swap.
> I'm trying to allocate 24 GB as shared_bufferes. I'm getting an error
> that I can not allocate memory (see below).

While this doesn't answer your question: why are you trying to do that?
AFAIK there is no evidence whatever that that's a good idea.  Try
measuring performance at, say, 1Gb, 8Gb, 16Gb of shared buffers and see
where the trend is going before you waste a lot of time fixing the kernel
parameters.

            regards, tom lane

Not sure if the kernel shared memory segment size is appropriate, you are allocating all your memory to the chunk.
 
With 32GB memory, effective_cache_size can be raised, higher, and you can go down on shared_buffers. Check this:
http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html
 
-anjan

    -----Original Message----- 
    From: Tomeh, Husam [mailto:htomeh@firstam.com] 
    Sent: Wed 12/14/2005 5:08 PM 
    To: pgsql-admin@postgresql.org 
    Cc: Tom Lane 
    Subject: [ADMIN] PG 8.1.1 Cannot allocate shared_buffers memory error
    
    

    
    I just installed postgres 8.1.1 on a dual optron Linux box running Linux 
    4 advanced server, with 32GB of RAM and 2GB of swap. 
    I'm trying to allocate 24 GB as shared_bufferes. I'm getting an error 
    that I can not allocate memory (see below). If I change my 
    shared_buffers to 16GB, postgres starts up with no issue. I'm trying to 
    understand why I'm getting the shared memory error at sizes above 16GB 
    whilst I have 32GB with appropriate (I think) settings of kernel 
    parameters. Any help is appreciated. Thanks... 

    My sysctl.conf has : 
      kernel.shmmax = 34359738368 
      kernel.shmall = 34359738368   (32GB). 

    And here's some of related postgresql.conf parameters: 

      shared_buffers = 2359296 
      work_mem = 16384 
      maintenance_work_mem = 2097152 
      max_connections = 100 
      effective_cache_size = 2621440 

    --- 
    Error: 

     FATAL:  could not create shared memory segment: Cannot allocate memory 
    [2005-12-14 13:56:03 PST|||] DETAIL:  Failed system call was 
    shmget(key=5432001, size=19760111616, 03600). 
    [2005-12-14 13:56:03 PST|||] 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 19760111616 
    bytes), reduce PostgreSQL's shared_buffers parameter (currently 2359296) 
    and/or its max_connections parameter (currently 100). 

    --- 
      
    Regards, 

      Husam Tomeh 
       
    ********************************************************************** 
    This message contains confidential information intended only for the use of the addressee(s) named above and may
containinformation that is legally privileged.  If you are not the addressee, or the person responsible for delivering
itto the addressee, you are hereby notified that reading, disseminating, distributing or copying this message is
strictlyprohibited.  If you have received this message by mistake, please immediately notify us by replying to the
messageand delete the original message immediately thereafter.
 

    Thank you. 


                                       FADLD Tag 
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