[[breaking-changes-2.3]]
== Breaking changes in 2.3

This section discusses the changes that you need to be aware of when migrating
your application to Elasticsearch 2.3.

* <<breaking_23_index_apis>>

[[breaking_23_index_apis]]
=== Mappings

==== Limit to the number of `nested` fields

Indexing a document with 100 nested fields actually indexes 101 documents as each nested
document is indexed as a separate document. To safeguard against ill-defined mappings
the number of nested fields that can be defined per index has been limited to 50.
This default limit can be changed with the index setting `index.mapping.nested_fields.limit`.
Note that the limit is only checked when new indices are created or mappings are updated. It
will thus only affect existing pre-2.3 indices if their mapping is changed.