Did a quick test of Ghostscript vs QPDF at PDF page splitting

qpdf won so hard it wasn't funny, even though it must be called once
per page to do the job. Perhaps Ghostscript interprets it as a call to
render the page?

time bash qpdf-test.fish ../tests/resources/multipage.pdf
        0.07 real         0.02 user         0.03 sys

time gs -sDEVICE=pdfwrite -dSAFER -o '%06d.pdf' ../tests/resources/multipage.pdf
        5.12 real         5.06 user         0.04 sys

ocrmypdf/qpdf.py

@@ -66,6 +66,11 @@ def get_npages(input_file):
 
 
 def split_pages(input_file, work_folder, npages):
+    """Split multipage PDF into individual pages.
+
+    Incredibly enough, this multiple process approach is about 70 times
+    faster than using Ghostscript.
+    """
     for n in range(int(npages)):
         args_qpdf = [
             'qpdf', input_file,