Practical VCL limits; giant URL->backend map

[Gordon Mohr]

The quite-possibly-nutty idea has occurred to me of auto-generating a 
VCL that maps each of about 18 million artifacts (incoming URLs) to 
1,2,or3 of what are effectively 621 backend locations. (The mapping is 
essentially arbitrary.)

Essentially, it would be replacing a squid url_rewrite_program.

Am I likely to hit any hard VCL implementation limits (in 
depth-of-conditional-nesting, overall size, VCL compilation overhead, 
etc.) if my VCL is ~100-200MB in size?

Am I overlooking some other more simple way to have varnish consult an 
arbitrary mapping (something similar to a squid url_rewrite_program)?

Thanks for any warnings/ideas.

- Gordon