void
CreateSharedMemoryAndSemaphores(void)
{
	PGShmemHeader *shim = NULL;
	if (!IsUnderPostmaster)
	{
    Size size;
    size = 100000;
    size = add_size(size, PGSemaphoreShmemSize(numSemas));
    size = add_size(size, SpinlockSemaSize());
    size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE, sizeof(ShmemIndexEnt)));
    size = add_size(size, dsm_estimate_size());
	  ……
		/*
		 * Create the shmem segment
		 */
		seghdr = PGSharedMemoryCreate(size, &shim);
	}
  ……
	/* Initialize dynamic shared memory facilities. */
	if (!IsUnderPostmaster)
		dsm_postmaster_startup(shim);
}