There is a data structure like nesting json but I can't define field name beforehand as of field name is defined by end user
I know if dynamic option is setting to true will make the fields number in mapping increase, so
1 How much is recommended maximum fields one index?
2 There are a lot of fields in one index, but there are a few not-null fields in one document in the index averagely. This condition will result in serious resource waste?