Mapping is the process of defining how a document, and the fields it contains, are stored and indexed. For instance, use mappings to define:
Each index has one mapping type which determines how the document will be indexed.
[6.0.0] Deprecated in 6.0.0. See Removal of mapping types .
A mapping type has:
Each field has a data
type which can be:
It is often useful to index the same field in different ways for different
purposes. For instance, a
string field could be indexed as
text field for full-text search, and as a
keyword field for
sorting or aggregations. Alternatively, you could index a string field with
standard analyzer, the
english analyzer, and the
This is the purpose of multi-fields. Most datatypes support multi-fields
Settings to prevent mappings explosionedit
Defining too many fields in an index is a condition that can lead to a mapping explosion, which can cause out of memory errors and difficult situations to recover from. This problem may be more common than expected. As an example, consider a situation in which every new document inserted introduces new fields. This is quite common with dynamic mappings. Every time a document contains new fields, those will end up in the index’s mappings. This isn’t worrying for a small amount of data, but it can become a problem as the mapping grows. The following settings allow you to limit the number of field mappings that can be created manually or dynamically, in order to prevent bad documents from causing a mapping explosion:
- The maximum number of fields in an index. The default value is
- The maximum depth for a field, which is measured as the number of inner
objects. For instance, if all fields are defined at the root object level,
then the depth is
1. If there is one object mapping, then the depth is
2, etc. The default is
- The maximum number of
nestedfields in an index, defaults to
50. Indexing 1 document with 100 nested fields actually indexes 101 documents as each nested document is indexed as a separate hidden document.
Fields and mapping types do not need to be defined before being used. Thanks
to dynamic mapping, new field names will be added automatically, just by
indexing a document. New fields can be added both to the top-level mapping
type, and to inner
The dynamic mapping rules can be configured to customise the mapping that is used for new fields.
You know more about your data than Elasticsearch can guess, so while dynamic mapping can be useful to get started, at some point you will want to specify your own explicit mappings.
Updating existing field mappingsedit
Other than where documented, existing field mappings cannot be updated. Changing the mapping would mean invalidating already indexed documents. Instead, you should create a new index with the correct mappings and reindex your data into that index.
A mapping could be specified when creating an index, as follows: