max-ixfr-ratio values

[Klaus Darilion]

max-ixfr-ratio introduced with 9.17.0 sounds like a workaround instead 
of a bugfix.

Anyway, can you recommend a sensible settings? I.e. when does the 
performance problem of "large" IXFR starts to happen? Does this depend 
on the ratio of the IXFR-size to zone-size, or does it depend on the 
size of the IXFR, regardless how big the zone is? (I hope the first 
thing, otherwise it would be better to define a max-ixfr-size instead of 
a ratio.)

I would like to know in more detail when the peformance drop happens, to 
find a proper value for the max-ixfr-ratio. Or do I have to play around 
with the value to find a compromise fast updates vs IXFR-triggered DoS?

Thanks
Klaus