Influence of ragel's code style outputs
Choosing different code style for compiling to C code has in some cases significant influence:

More information on code styles in chapter 5.11 in ragel guide: https://www.colm.net/files/ragel/ragel-guide-6.9.pdf
Source file compilation with gcc and clang
Final time is average value of 10 compilations.

Zscanner in use
On charts below you can see how code style, compiler and compiler options can influence time needed for zscanner to process zone file. To accomplish accurate measurement, zscanner was tested 5 times on the sample zone file, and average value is final outcome of the test.

Try it your self if you wish
Required changes: ~/knot-dns/src/zscanner/ Makefile.am needs to be edited:
This section:
if FAST_PARSER
scanner.c: scanner.c.g2
cp $(srcdir)/$@.g2 $@
@echo "NOTE: Compilation of scanner.c can take several minutes!"
else
scanner.c: scanner.c.t0
cp $(srcdir)/$@.t0 $@
endif
for: scanner.c: scanner.c
Unzip in ~/knot-dns/scripts/
gcc-clang-tests.zip
Used zone file
se.zone - 861,9 MB
https://zonedata.iis.se/
Online tools used for charts
https://live.amcharts.com
http://www.onlinecharttool.com