GNU并行不会产生作业

Question

After an upgrade to Debian 8.6 Jessie the GNU parallel script suddenly stopped parallelizing to more than 2 jobs with the --pipe and -L options.

Before the upgrade the command:

cat file_with_1064_lines.txt | parallel -L10 -j5 -k -v --pipe "wc -l"

spawned 5 processes, which output this:

wc -l
10
wc -l
10
...

The same command after the upgrade:

wc -l
1060
wc -l
4

(The two values above change with respect to the -L option value -- the first is L*floor(1064/L) and the second is 1064 mod L , but there always only two processes outputting.)

The same is observed independently of the parallel version (tested the latest and one from 2013).

PS.

$ uname -a

Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/Linux

$ parallel --version

GNU parallel 20161222

Answer 1

-L is the record size. The bug was fixed around 20130122. What you want is to read 1 record of 10 lines:

parallel -L10 -N1 -j5 -k -v --pipe wc -l

or 10 records of 1 line:

parallel -L1 -N10 -j5 -k -v --pipe wc -l