$ NUM_THREADS=6 ./llil4vec2 big?.txt big?.txt big?.txt >f4vec.tmp
llil4vec2 (fixed string length=6) start
use OpenMP
use boost sort
get properties      time : 1.9719 secs
sort properties     time : 2.27273 secs
vector reduce       time : 0.201546 secs
vector stable sort  time : 0.500317 secs
write stdout        time : 0.721466 secs
total               time : 5.66814 secs
$ NUM_THREADS=6 ./llil4map big?.txt big?.txt big?.txt >f4map.tmp
llil4map start
use phmap::parallel_flat_hash_map
use OpenMP
use boost sort
get properties      time : 5.33992 secs
finish merging      time : 2.20465 secs
vector stable sort  time : 1.60465 secs
write stdout        time : 1.21258 secs
total               time : 10.3622 secs
$ diff f4map.tmp f4vec.tmp
$ ls -l f4map.tmp f4vec.tmp
-rw-r--r--  183490874   Feb  1 09:38 f4map.tmp
-rw-r--r--  183490874   Feb  1 09:37 f4vec.tmp
$ ls -l big*.txt
-rw-r--r--  31636800 Jan 16 18:26 big1.txt
-rw-r--r--  31636800 Jan 16 18:26 big2.txt
-rw-r--r--  31636800 Jan 16 18:26 big3.txt
-rw-r--r--  31636800 Feb  1 09:33 big4.txt
-rw-r--r--  31636800 Feb  1 09:31 big5.txt
-rw-r--r--  31636800 Feb  1 09:31 big6.txt