What is considered a "large arbitrary set of keys", for the nested mapping?

On Nested field type | Elasticsearch Guide [7.13] | Elastic you can find this statement: "When ingesting key-value pairs with a large, arbitrary set of keys, you might consider modeling each key-value pair as its own nested document with key and value fields."

My question now is, what is considered a "large arbitrary set of keys" in this context? Are we talking tens, or hundreds or thousands, or even bigger?

I do not know the answer but suspect it depends on whether you data is static or you update documents frequently. As each nested component within the main document is indexed as a separate document behind the scenes and the full document with all nested components is reindexed for each update it can get slow as the number of nested documents grow. If your data is static and not updated it may be less of a concern although having very large documents can be problematic.

Then I give some numbers and details, I'm talking about docs with roughly 4000 key-value pairs, 95% keywords, 2.5% each numbers or simple value lists, we never update, only insert into the hourly index and delete the index after a week.

The amount of nested objects inside of an doc is about 20 with about 20 key-value pairs each, so only 10% of the overall doc size...