ectory).
        Not all values are supported on all platforms; the first supported
        option is usually the default for that platform.  The use of the
        <code class="literal">mmap</code> 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
        <code class="literal">pg_dynshmem</code> director