The way that the exists filter works is by merging all postings lists. missing just wraps an exists filter into a not filter.

Merging all postings lists can however be very slow on high-cardinality fields. I think there are two ways to fix it:

1. make these filters run on top of field data,
2. or add a new metadata field that we could eg. call _field_names that would index all field names of a document.

Working on field data has the drawback of requiring a lot of stuff to be loaded into memory if the field doesn't have doc values, and the returned filter cannot skip.

I tend to like indexing field names because it would not load anything into memory with a default setup, and the returned filter could skip efficiently since it would be based on a postings list. But unfortunately it could not be used on indices that have been created before we introduce this new metadata field.