I'm getting the error like this:
nginx: [emerg] could not build the map_hash, you should increase either map_hash_max_size: 2048 or map_hash_bucket_size: 64

I solved it by setting large values to those two variables, but I didn't quite the why. Could someone explain more about those two values? Thanks!

map_hash_bucket_size

"The directive sets the maximum size in a hash table to map variables"
What exactly is the max size here? Size of how many elements can be stored in hash table?

map_hash_max_size

"The directive sets the maximum size of a hash table to hold the variable map"
Then how about the max size here?