Use “LC_ALL=C” to improve performance

Using “LC_ALL=C” can improve some program’s performance. The following is the test without LC_ALL=C of join program:

$ locale
LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=
$ sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"
$ time join 1.sorted 2.sorted > 1-2.sorted.aggregated

real    0m49.903s
user    0m48.427s
sys 0m0.786s

And this one is using “LC_ALL=C“:

$ sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"
$ time LC_ALL=C join 1.sorted 2.sorted > 1-2.sorted.aggregated

real    0m12.752s
user    0m5.628s
sys 0m0.971s

some good references about this topic are Speed up grep searches with LC_ALL=C and Everyone knows grep is faster in the C locale.