shared_memory_size is a preset configuration parameter reporting the size of the main shared memory area.
shared_memory_size was added in PostgreSQL 15.
shared_memory_size is computed at runtime and reports the size of the server's main shared memory area. This includes the amount of shared memory allocated by extensions as this is calculated after processing
The reported value is rounded up to the nearest megabyte.
Value reported by
shared_memory_size on a default installation with
postgres=# SHOW shared_memory_size; shared_memory_size -------------------- 145MB (1 row)