Understanding high memory usage for fielddata cache

Hello,

I am looking for help with understanding why the fielddata cache for a certain field is so large.

Towards that end, I was wondering if anyone could describe to one or both of:

  • A formula for estimating the usage of the fielddata cache.

  • A description of the default, in-memory data structure used to store the cache.

I'm looking to properly grok this, so please feel free to use whatever level of techical detail you think is needed.

Thanks!

Morgan