a single rrd file is not too large, but I assume this should not be the case
in general. Otherwhise we would have to sync and release while writing all
the unknown data. */
+ fflush(rrd_file);
fdatasync(fileno(rrd_file));
if (0 != posix_fadvise(fileno(rrd_file), rrd_head_size, 0, POSIX_FADV_DONTNEED)) {
rrd_set_error("setting POSIX_FADV_DONTNEED on '%s': %s",file_name, rrd_strerror(errno));