Too Many Open Files

The number of concurrent network requests (MAX_CONCURRENCY) is set to 128 by default.

Every network request maps to an open socket, which is represented as a file on UNIX systems. If you see error messages like error trying to connect: tcp open error: Too many open files (os error 24) then you ran out of file handles.

You have two options:

1. Lower the concurrency by setting --max-concurrency to something more conservative like 32. This works, but it also comes with a performance penalty.
2. Increase the number of maximum file handles. See instructions here or here.