Pulp

There are reports that the download concurrency is too high, like this one: https://pulp.plan.io/issues/7186#note-4

So we should lower the concurrency limit. We need to balance the stability gained from a lower concurrency against the lost speeds from parallel fetching.

Can someone measure the runtime of a policy=immediate sync with the following download_concurrency values:

20, 15, 10, 7, 5, 3

Pulp2 had a value of 5. Other download softwares like bandersnatch have a value of 3, so one of those is the most likely choice. We should understand how the performance degrades though so running this test would be nice.