Avoiding "Warning: Starting 10 extra processes takes > 2 sec."

[Alexander Søndergaard]

Hello,

I've run into a small issue when using parallel.

I've got a pipe that blocks due to the presence of a sort filter.
Hence, parallel decides to avoid spawning multiple parallel tasks, as
it doesn't receive any input till a few seconds later:

cat longfile | sort | uniq | parallel -j 20 'echo {} | ruby task.rb'

Warning: Starting 10 extra processes takes > 2 sec.
Limiting to 1 jobs in parallel.

Can I avoid this warning other than simply splitting the pipeline into
two commands? I've checked the man page, but I haven't found any
suitable answers.

Thanks.

Best,
A. S.