postgresql shared memory settings
postgresql, shared-memory
Solution
Increasing `SHMMNI` will not help, it's the second part of the hint that matters here.
Get your system's page size with the shell command `getconf PAGE_SIZE`. Usually it's 4096. Multiply that by `SHMALL`.
In your case that should be 2097152 * 4096 = 8589934592, which is exactly 8Gb. That's your current maximum shared memory, independently of `SHMMNI`.
PostgreSQL error message indicates that it needs a bit more than that.
Conclusion: increase `SHMALL`.
Problem
Hi all! We have at present the following parameters related to shared memory: postgres ``` shared_buffers = 7GB max_connections = 1 500 max_locks_per_transaction = 1 024 max_prepared_transactions = 0 (not set) ``` system ``` SHMALL = 2 097 152 SHMMAX = 17 670 512 640 SHMMNI = 4096 ``` The amount of RAM is 24 693 176k We need to increase max_connections to 3 000. 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, I believe that all these parameters correlate somehow, so do we need to change any other parameters accordingly? Thanks in advance, Alexander