Specifies the dynamic shared memory implementation that the server should use. Possible values are
posix (for POSIX shared memory allocated using
sysv (for System V shared memory allocated via
windows (for Windows shared memory),
mmap (to simulate shared memory using memory-mapped files stored in the data directory), and
none (to disable this feature). Not all values are supported on all platforms; the first supported option is the default for that platform. The use of the
mmap option, which is not the default on any platform, is generally discouraged because the operating system may write modified pages back to disk repeatedly, increasing system I/O load; however, it may be useful for debugging, when the
pg_dynshmem directory is stored on a RAM disk, or when other shared memory facilities are not available.