PostgreSQL 10 High Performance - Third Edition

Kernel semaphores

While not a memory allocation figure, another occasional sysctl tweaking requirement for PostgreSQL is to increase the number of available systems, an object used for process communication.

The defaults on a recent Linux system look like this:

$ ipcs -l 
... 
------ Semaphore Limits -------- 
max number of arrays = 128 
max semaphores per array = 250 
max semaphores system wide = 32000 
max ops per semop call = 32 
max ops per semop call = 100 
semaphore max value = 32767 
... 

One of the parts trimmed from the icps output also shows the shared memory limits, so you can also double-check them with it. Setting higher semaphore limits is done with a kernel parameter that combines the main four limits here into one line. The last shown ...