R: repeated out of shared memory error - not related to max_locks_per_transaction

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I did.
This is a dedicated server.

root@pg:/var/log/postgresql# ipcs -pm

------ Shared Memory Creator/Last-op PIDs --------
shmid      proprietario cpid       lpid
131072     postgres   12879      15299

root@pg:/var/log/postgresql# ipcs -m

------ Segm. Memoria Condivisa --------
chiave     shmid      proprietario perms      byte       nattch     stato
0x0052e2c1 131072     postgres   600        56         83

-----Messaggio originale-----
Da: 066ce286@xxxxxxx <066ce286@xxxxxxx> 
Inviato: venerdì 20 luglio 2018 14:01
A: pgsql-admin@xxxxxxxxxxxxxxxxxxxx
Oggetto: Re: repeated out of shared memory error - not related to max_locks_per_transaction

Hi,

Try to run

ipcs -m
(and also ipcs -pm)


To check who and wich process is using the shm.


----- Mail original -----
De: "Alfonso Moscato" <alfonso.moscato@xxxxxxxxxxx>
À: pgsql-admin@xxxxxxxxxxxxxxxxxxxx
Envoyé: Vendredi 20 Juillet 2018 13:14:53
Objet: repeated out of shared memory error - not related to max_locks_per_transaction

We are getting crazy with "out of shared memory" errors, and we can't figure the reason.
We have postgresql "PostgreSQL 9.6.9 on x86_64-pc-linux-gnu (Ubuntu 9.6.9-2.pgdg16.04+1), compiled by gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609, 64-bit", the server has 92gb of ram, it is a mixed environment (mostly OLTP, with some DW), with 100 sessions constantly open (a CRM) and some long queries run every half an hour.
Everything works fine, except that after 1 day and half we start receiving a lot of "out of shared memory" messages.
I am sure it is not related with the usual max_locks_per_transaction issue, because we have set max_locks_per_transaction to 384, and when we receive these messages we have no more than 50/100 locks totally.
Restarting the server usually works fine for one day and hal more, and then messages restart.
Looking at the log, we see that this error starts casually, sometimes on very small queries, returning some kbytes of data.
We have tried a lot of different configurations. we have tried with pgtune and pgconfig 2.0.

Currently, we have: 
max_connections = 200
shared_buffers = 23GB
effective_cache_size = 69GB
maintenance_work_mem = 2GB
checkpoint_completion_target = 0.9
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 4
effective_io_concurrency = 2
work_mem = 60293kB
min_wal_size = 2GB
max_wal_size = 4GB
max_worker_processes = 4
max_parallel_workers_per_gather = 2
max_locks_per_transaction = 384
but we tried with work_mem to 130mb, shared_buffer to a maximum fo 40gb, effective_cache to 4gb

shared memory limits are very big: 
max number of segments = 4096
max seg size (kbytes) = 18014398509465599 max total shared memory (kbytes) = 18014398442373116 min seg size (bytes) = 1

thanks









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