Documentation of section "Limiting the number of nested fields" is not understandable and it is an important topic

[alexmorosmarco]

Elasticsearch version (bin/elasticsearch --version): 2.4 and all the following ones

Plugins installed: []

JVM version (java -version):

OS version (uname -a if on a Unix-like system):

Description of the problem including expected versus actual behavior:
Hi, I write because i think there is an important part of the documentation that I see really weak because I think the explanation is not good enough to understand it and it is an important topic.
I am talking about the section "Limiting the number of nested fields" of the documentation (https://www.elastic.co/guide/en/elasticsearch/reference/6.1/nested.html#_limiting_the_number_of_literal_nested_literal_fields).
Let's take into account the given example having an array named user, defined with nested datatype, that can have user objects inside.

It mentions that Indexing a document with 100 nested fields actually indexes 101 documents as each nested document is indexed as a separate document..
What does that sentence mean with "100 nested fields"?

• is it talking about a case where we would have 100 arrays like user, car and any other arrays?
• or is it talking about having 100 user objects inside the array user?

It also mentions To safeguard against ill-defined mappings the number of nested fields that can be defined per index has been limited to 50.
What does that sentence mean?

• is it talking about that we can only define 50 arrays as nested datatype in a document?
• or about that inside an array defined as nested we can only have 50 objects?
• In addition, taking into account that this is the documentation of the nested datatype, I think it should explain that the 50 default value is stored in the property index.mapping.nested_fields.limit.

Please could you answer my question and also explain better this topic in the documentation? Maybe solving those doubts and also writing some examples would be fine.
I see the same problem in the documentation of ElasticSearch 2.4, could you also improve it?

As an extra, in the documentation of ElasticSearch 2.4 I do not see any reference in the Mappings documentation that explains about the index.mapping.nested_fields.limit parameter.
Couldn't be described somewhere? I first searched for it in the "Index Modules" docu and then in the "Mappings" docu but without luck.

Thanks a lot!

[andyb-elastic]

@elastic/es-search-aggs

[ludovicth]

It mentions that Indexing a document with 100 nested fields actually indexes 101 documents as each nested document is indexed as a separate document..
What does that sentence mean with "100 nested fields"?

is it talking about a case where we would have 100 arrays like user, car and any other arrays?
or is it talking about having 100 user objects inside the array user?

=> it is talking about having 100 user objects inside the array user.

[HunderlineK]

Further more, what happens if there are nested items within a nested item?

Let's say, user has 10 blogs and each blog has 10 comments; does that create 100 documents and violate the limit if it is set to 50?