GNU Parallel Usage in M1Mac running OSX 13.1-CodePudding

I have a brew installed gnu parallel in MacStudio;

(base) ~ % brew info parallel
==> parallel: stable 20221222 (bottled), HEAD
Shell command parallelization utility
https://savannah.gnu.org/projects/parallel/

(base) ~ % parallel --version
GNU parallel 20221222
Copyright (C) 2007-2022 Ole Tange, http://ole.tange.dk and Free Software
Foundation, Inc.

I played pipe-part with sed as follows;

parallel -a -eta -vv SRR8758324_2.fastq -k --block 30M --pipe-part 'sed "s/ .*/ /"' > SRR8758324_2.mod.fastq

When I monitored a cpu usage by htop, I could see all the 20 cores light up.

However, when I fired a following;

parallel -j 20 --eta  -vv 'sed "s/ .*/ /"'  :::  SRR8758324_2.fastq > SRR8758324_2.mod.fastq

only a single core was used. I'd really appreciate pointers to what I am missing.

                  'c.          
                 ,xNMM.          
               .OMMMMo           OS: macOS 13.1 22C65 arm64
               OMMM0,            Host: Mac13,2
     .;loddo:' loolloddol;.      Kernel: 22.2.0
   cKMMMMMMMMMMNWMMMMMMMMMM0:    Uptime: 9 hours, 19 mins
 .KMMMMMMMMMMMMMMMMMMMMMMMWd.    Packages: 181 (brew)
 XMMMMMMMMMMMMMMMMMMMMMMMX.      Shell: zsh 5.9
;MMMMMMMMMMMMMMMMMMMMMMMM:       Resolution: 3440x1440
:MMMMMMMMMMMMMMMMMMMMMMMM:       DE: Aqua
.MMMMMMMMMMMMMMMMMMMMMMMMX.      WM: Quartz Compositor
 kMMMMMMMMMMMMMMMMMMMMMMMMWd.    WM Theme: Blue (Light)
 .XMMMMMMMMMMMMMMMMMMMMMMMMMMk   Terminal: iTerm2
  .XMMMMMMMMMMMMMMMMMMMMMMMMK.   Terminal Font: Monaco 10
    kMMMMMMMMMMMMMMMMMMMMMMd     CPU: Apple M1 Ultra
     ;KMMMMMMMWXXWMMMMMMMk.      GPU: Apple M1 Ultra
       .cooc,.    .,coo:.        Memory: 3099MiB / 131072MiB

CodePudding user response：

You're just running one instance of sed on one file in the second example.

In the first one, because of --pipe-part, you are asking GNU Parallel to split the file into chunks and process each one in a new job.