Re: New PG14 server won't start with >2GB shared_buffers

[Chris Hoover <chrish@xxxxxxxxxx>]

MichaelDBA,

The issue is PostgreSQL won’t start with a large shared_buffer.  If I try to start using more than ~2GB, it won’t start (See errors in original post).  That’s the issue we are trying to resolve.  

This is a large server running on bare metal that won’t let PG start with a large shared_buffer setting.  Until we can resolve this, we can’t upgrade to this server.

Thanks,

Chris Hoover

Senior DBA

AWeber.com

Cell: (803) 528-2269

Email: chrish@xxxxxxxxxx

On Feb 25, 2023, at 9:05 AM, MichaelDBA <MichaelDBA@xxxxxxxxxxx> wrote:

I just don't get what all this fuss is about trying to get PG up on the smallest possible values for shared_buffers, especially considering this person has 1 TB of memory?

Chris Hoover wrote on 2/25/2023 8:07 AM:

Ron,

Honestly, I grabbed 500MB to get the database up, by this time I was very frustrated and just wanted it up.  :)  I think I was at 1500MB and it still would not start.  So to save what was left of my evening out, I just picked 500.  

Here is shmall:

kernel.shmall = 17179869184

Thanks,

Chris Hoover

Senior DBA

AWeber.com

Cell: (803) 528-2269

Email: chrish@xxxxxxxxxx

On Feb 25, 2023, at 5:25 AM, Ron <ronljohnsonjr@xxxxxxxxx> wrote:

Why did you have to drop shared buffers to 500MB, instead of something just below 2GB?

And what's "your kernel's SHMALL parameter"?

On 2/24/23 20:08, Chris Hoover wrote:

Hello All,

Have a strange issue that I can not solve.

I have a new server that has 1TB ram (not a typo).  I have been fighting with this evening to start up with a shared_buffer setting over 2GB.  When the memory allocation  breaks 2GB, the database won’t start.  I’ve dropped it down to 500M to get the database online.  We’ve tried both SysV memory and mmap memory.

Any ideas on what is going on and how to resolve?  I’m sure I’m missing something obvious, but it is totally eluding me.

OS: Ubuntu 18.04

Memory:  1007GB

CPU: Intel(R) Xeon(R) CPU           X7550  @ 2.00GHz (64 cores total)

Kernel Memory:

kernel.shmmax = 274877906944

kernel.shmall = 17179869184

Postgres Config:

                  name                                  |                  setting

 autovacuum_max_workers                 | 3

 autovacuum_work_mem                     | -1

 effective_cache_size                           | 98992128

 fsync                                                    | on

 full_page_writes                                  | on

 maintenance_work_mem                    | 2097152

 shared_buffers                                    | 64000

 shared_memory_type                         | sysv

 temp_buffers                                       | 4096

 wal_buffers                                         | 2048

 work_mem                                          | 119990

If you need additional parameters, please ask

SysV Error:

Feb 25 01:55:16 appdb-server01.production.aweberint.com postgres[34680]: FATAL:  could not create shared memory segment: Cannot allocate memory

DETAIL:  Failed system call was shmget(key=2359323, size=2063564800, 03600).

HINT:  This error usually means that PostgreSQL's request for a shared memory segment exceeded your kernel's SHMALL parameter.  You might need to reconfigure the kernel with larger SHMALL.

Mmap Error:

FATAL:  could not map anonymous shared memory: Cannot allocate memory

HINT:  This error usually means that PostgreSQL's request for a shared memory segment exceeded available memory, swap space, or huge pages. To reduce the request size (currently 1635737600 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.

Thanks,

Chris Hoover

Senior DBA

AWeber.com

Cell: (803) 528-2269

Email: chrish@xxxxxxxxxx

-- 
Born in Arizona, moved to Babylonia.

Regards,

Michael Vitale

Michaeldba@xxxxxxxxxxx

703-600-9343

  
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