Hi all!
We have at present the following parameters related to shared memory:
postgres
shared_buffers = 7GB
max_connections = 1500
max_locks_per_transaction = 1024
max_prepared_transactions = 0 (not set)
system
SHMALL = 2097152
SHMMAX = 17 670 512 640
SHMMNI = 4096
The amount of RAM is 24 693 176k
We need to increase max_connections to 3000. When we tried to do this we got an error
[1-1] FATAL: could not create shared memory segment: No space left on device
[2-1] DETAIL: Failed system call was shmget(key=5432001, size=8964661248, 03600).
[3-1] HINT: This error does *not* mean that you have run out of disk space. It occurs either if all available shared memory IDs have been taken, in which case you need to raise the SHMMNI parameter in your kernel, or because the system's overall limit for shared memory has been reached. If you cannot increase the shared memory limit, reduce PostgreSQL's shared memory request (currently 8964661248 bytes), perhaps by reducing shared_buffers or max_connections.
The PostgreSQL documentation contains more information about shared memory configuration.
The hint proposes to increase SHMMNI kernel parameter, but I'm not sure about how much to add :) Also, do we need to change any other parameters accordingly?
Thanks in advance,
Alexander