pigz usage

sudo apt install pigz

# -0 to -9 : compression level
#-p n : number of used cores
# -k : keep source file

# compress file
pigz -5 -p 8 -k filename
# to generate filename.gz

# compress doc
tar cvf - doc1 doc2 | pigz -p 8 -k > doc.tar.gz

# decompress .gz
pigz -d filename.gz

# decompress .tar.gz
tar zxvf filename.tar.gz