Another postgres not starting: "could not map anonymous shared memory"

Question

I noticed there are several questions about Postgres (10) not able to boot because of the shared memory; despite that I couldn't really make it run. Now everytime I try to start the cluster I keep getting this error:

2021-10-24 10:13:43.269 UTC  [11253] FATAL:  could not map anonymous shared memory: Cannot allocate memory
2021-10-24 10:13:43.269 UTC  [11253] 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 5507432448 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.

I tryed to check and modify the kernel shmall parameter, but didn't work.

~$ cat /proc/sys/kernel/shmall
18446744073692774399

~$ cat /proc/sys/kernel/shmmax
18446744073692774399

I can't reduce the memory into the config file because these are the settings I must use although I tryied anyway but without success (I even used the minimum values).

Thanks for the help!

EDIT 1:

Ok, I found something strange:

I purged postgresql completely from the system
I reinstalled postgresql
Started the cluster and everything went well
Stopped the cluster and edited the configuration file with the settings I need
Tryed to start the cluster again but got the same error
Reverted back to the default configuration file but still getting the same error. Why is this happening?

The system has 16 GB of RAM.

EDIT 2: ADDING DETAILS

Ok so basically I had to migrate a postgresql database by moving the data directory. That's the only thing it could be done. After moving the data folder completely here's the error. I noticed there weren't a swap memory so I created it but still same error.

The shared memory and segment between the two server are basically identical. When I start the cluster It immediately fails, so maybe this can be a clue for you. The destination server is an EC2 machine.

I don't know what else I can do..

EDIT 3: OTHER DETAILS

This is what the command lsipc shows:

RESOURCE DESCRIPTION                                              LIMIT USED  USE%
MSGMNI   Number of message queues                                 32000    0 0.00%
MSGMAX   Max size of message (bytes)                               8192    -     -
MSGMNB   Default max size of queue (bytes)                        16384    -     -
SHMMNI   Shared memory segments                                    4096    0 0.00%
SHMALL   Shared memory pages                       18446744073692774399    0 0.00%
SHMMAX   Max size of shared memory segment (bytes) 18446744073692774399    -     -
SHMMIN   Min size of shared memory segment (bytes)                    1    -     -
SEMMNI   Number of semaphore identifiers                          32000    0 0.00%
SEMMNS   Total number of semaphores                          1024000000    0 0.00%
SEMMSL   Max semaphores per semaphore set.                        32000    -     -
SEMOPM   Max number of operations per semop(2)                      500    -     -
SEMVMX   Semaphore max value                                      32767    -     -

These values are the same of the source machine I'm trying to migrate. The data directory is identical with the original one, but everythime I go with this command:

sudo pg_ctlcluster 10 main start

I get the same error. I really need help!

Thank you for the help. I replaced my config file with the original one but still I get the same error. — Federico Loro, Oct 24 '21 at 11:42
Does the reported number 5507432448 change when you change the memory settings? If not, then the config file you are changing is not the correct one. — jjanes, Oct 24 '21 at 14:18
Yes, with the default configuration file that value is smaller. — Federico Loro, Oct 24 '21 at 15:30
I updated the main thread with the result of the command lsipc — Federico Loro, Oct 26 '21 at 15:06

Laurenz Albe · Answer 1 · 2023-03-14T03:33:12.333

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As the documentation says:

By default, PostgreSQL allocates a very small amount of System V shared memory, as well as a much larger amount of anonymous mmap shared memory.

So unless you changed shared_memory_type to sysv, your kernel configuration is pretty irrelevant.

I can think of two possible reasons for the error:

The kernel does not have enough memory available to satisfy the request. This could be because shared_buffers is set too large, or because other processes use too much memory, or because there is already a lot of shared memory mapped for other purposes.
You configured huge_pages = on, but there are no huge pages defined.

edited Mar 14 '23 at 03:33

answered Oct 25 '21 at 04:13

Laurenz Albe

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Ok, thank you for answering; At the moment the shared_buffers has a value of 128 MB and the dynamic_shared_memory_type is sysv. Still getting the same error. – Federico Loro Oct 25 '21 at 06:04
You could change the setting back to the default `mmap`. Then you don't have to fiddle with Systam V shared memory settings. – Laurenz Albe Oct 25 '21 at 06:45
It was set on POSIX before, but still the same issue. – Federico Loro Oct 25 '21 at 11:07
Then you don't have the required memory on your machine. Perhaps you are in a limited environment. – Laurenz Albe Oct 25 '21 at 11:39
Thanks again for your time. I edited the post because I found something weird happening. I think I'm missing something. – Federico Loro Oct 25 '21 at 11:49

score 0 · Answer 2 · answered Mar 13 '23 at 13:24

I had similar problem. As you working with Postgresql DB you should create/provide swap space with same size or bigger than shared_buffers value.

How to create swapfile (ex. 8GB):

sudo fallocate -l 8G /.swapfile; sudo chmod 600 /.swapfile; sudo mkswap /.swapfile; sudo swapon /.swapfile;

then add swapfile to /etc/fstab:

/.swapfile swap swap defaults 0 0

score 0 · Answer 3 · answered Jul 18 '23 at 15:21

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Rebooting my server fixed this for me after hours of trying different confugurations with no luck.

sudo reboot

answered Jul 18 '23 at 15:21

Atehe

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score 0 · Answer 4 · answered Aug 10 '23 at 04:52

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In my case it was postgresql.auto.conf file I've created myself with the ALTER SYSTEM command. Cleaning up this file contents reset settings to system default and error fixed.

answered Aug 10 '23 at 04:52

olegabr

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Another postgres not starting: "could not map anonymous shared memory"

4 Answers4