RE: Memory issues with PostgreSQL 15

Hi Francisco,
Thank you for your advice. I used "ipcs" to get more readable information about the shared memory:

# ipcs -m -l --human

------ Shared Memory Limits --------
max number of segments = 4096
max seg size = 16E
max total shared memory = 16E
min seg size = 1B

# ipcs -m

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x04000194 35 postgres 600 56 19

# ipcs -m -i 35

Shared memory Segment shmid=35
uid=26 gid=26 cuid=26 cgid=26
mode=0600 access_perms=0600
bytes=56 lpid=7653 cpid=3875 nattch=19
att_time=Tue May 28 22:56:35 2024
det_time=Tue May 28 22:56:35 2024
change_time=Tue May 28 07:59:59 2024

As far as I understand, there is no upper limit to the size of the shared memory. The database only holds a single shared memory segment, which doesn't seem to have a relevant size.
I am surprised to see this since I would have expected much more shared memory to be used by the database. Is there anything in the configuration that prevents the shared memory from being used?

Best,
Christian

-----Original Message-----
From: Francisco Olarte <folarte(at)peoplecall(dot)com>
Sent: Tuesday, May 28, 2024 7:15 PM
To: Christian Schröder <christian(dot)schroeder(at)wsd(dot)com>
Cc: pgsql-general(at)lists(dot)postgresql(dot)org; Eric Wong <eric(dot)wong(at)wsd(dot)com>
Subject: Re: Memory issues with PostgreSQL 15

[EXTERNAL]

Hi Christian:

On Tue, 28 May 2024 at 18:40, Christian Schröder <christian(dot)schroeder(at)wsd(dot)com> wrote:

> <2024-05-21 11:34:46 CEST - mailprocessor> ERROR: could not resize
> shared memory segment "/PostgreSQL.2448337832" to 182656 bytes: No
> space left on device

This hints at some shm function getting an ENOSPC: Coupled with...

> I thought this could all be related to our "shared_buffers" setting, so I increased it to 8 GB. This almost immediately (after a few minutes) gave me these errors:

A faster fail when increasing it I would start by checking your IPC shared memory limits are ok, especially if you upgraded something in the OS when going from 9 to 15, which seems likely.

IIRC in linux you can read them in /proc/sys/kernel/shm*, and they were configured via sysctl.

Francisco Olarte.

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