Core Typesedit

Each JSON field can be mapped to a specific core type. JSON itself already provides us with some typing, with its support for string, integer/long, float/double, boolean, and null.

The following sample tweet JSON document will be used to explain the core types:

{
    "tweet" {
        "user" : "kimchy"
        "message" : "This is a tweet!",
        "postDate" : "2009-11-15T14:12:12",
        "priority" : 4,
        "rank" : 12.3
    }
}

Explicit mapping for the above JSON tweet can be:

{
    "tweet" : {
        "properties" : {
            "user" : {"type" : "string", "index" : "not_analyzed"},
            "message" : {"type" : "string", "null_value" : "na"},
            "postDate" : {"type" : "date"},
            "priority" : {"type" : "integer"},
            "rank" : {"type" : "float"}
        }
    }
}

Stringedit

The text based string type is the most basic type, and contains one or more characters. An example mapping can be:

{
    "tweet" : {
        "properties" : {
            "message" : {
                "type" : "string",
                "store" : "yes",
                "index" : "analyzed",
                "null_value" : "na"
            },
            "user" : {
                "type" : "string",
                "index" : "not_analyzed",
                "norms" : {
                    "enabled" : false
                }
            }
        }
    }
}

The above mapping defines a string message property/field within the tweet type. The field is stored in the index (so it can later be retrieved using selective loading when searching), and it gets analyzed (broken down into searchable terms). If the message has a null value, then the value that will be stored is na. There is also a string user which is indexed as-is (not broken down into tokens) and has norms disabled (so that matching this field is a binary decision, no match is better than another one).

The following table lists all the attributes that can be used with the string type:

Attribute Description

index_name

The name of the field that will be stored in the index. Defaults to the property/field name.

store

Set to yes to store actual field in the index, no to not store it. Defaults to no (note, the JSON document itself is stored, and it can be retrieved from it).

index

Set to analyzed for the field to be indexed and searchable after being broken down into token using an analyzer. not_analyzed means that its still searchable, but does not go through any analysis process or broken down into tokens. no means that it won’t be searchable at all (as an individual field; it may still be included in _all). Setting to no disables include_in_all. Defaults to analyzed.

term_vector

Possible values are no, yes, with_offsets, with_positions, with_positions_offsets. Defaults to no.

boost

The boost value. Defaults to 1.0.

null_value

When there is a (JSON) null value for the field, use the null_value as the field value. Defaults to not adding the field at all.

norms.enabled

Boolean value if norms should be enabled or not. Defaults to true for analyzed fields, and to false for not_analyzed fields.

norms.loading

Describes how norms should be loaded, possible values are eager and lazy (default). It is possible to change the default value to eager for all fields by configuring the index setting index.norms.loading to eager.

omit_term_freq_and_positions

Boolean value if term freq and positions should be omitted. Defaults to false. Deprecated since 0.20, see index_options.

index_options

Available since 0.20. Allows to set the indexing options, possible values are docs (only doc numbers are indexed), freqs (doc numbers and term frequencies), and positions (doc numbers, term frequencies and positions). Defaults to positions for analyzed fields, and to docs for not_analyzed fields. Since 0.90 it is also possible to set it to offsets (doc numbers, term frequencies, positions and offsets).

analyzer

The analyzer used to analyze the text contents when analyzed during indexing and when searching using a query string. Defaults to the globally configured analyzer.

index_analyzer

The analyzer used to analyze the text contents when analyzed during indexing.

search_analyzer

The analyzer used to analyze the field when part of a query string. Can be updated on an existing field.

include_in_all

Should the field be included in the _all field (if enabled). If index is set to no this defaults to false, otherwise, defaults to true or to the parent object type setting.

ignore_above

The analyzer will ignore strings larger than this size. Useful for generic not_analyzed fields that should ignore long text. (since @0.19.9).

position_offset_gap

Position increment gap between field instances with the same field name. Defaults to 0.

The string type also support custom indexing parameters associated with the indexed value. For example:

{
    "message" : {
        "_value":  "boosted value",
        "_boost":  2.0
    }
}

The mapping is required to disambiguate the meaning of the document. Otherwise, the structure would interpret "message" as a value of type "object". The key _value (or value) in the inner document specifies the real string content that should eventually be indexed. The _boost (or boost) key specifies the per field document boost (here 2.0).

Numberedit

A number based type supporting float, double, byte, short, integer, and long. It uses specific constructs within Lucene in order to support numeric values. The number types have the same ranges as corresponding Java types. An example mapping can be:

{
    "tweet" : {
        "properties" : {
            "rank" : {
                "type" : "float",
                "null_value" : 1.0
            }
        }
    }
}

The following table lists all the attributes that can be used with a numbered type:

Attribute Description

type

The type of the number. Can be float, double, integer, long, short, byte. Required.

index_name

The name of the field that will be stored in the index. Defaults to the property/field name.

store

Set to yes to store actual field in the index, no to not store it. Defaults to no (note, the JSON document itself is stored, and it can be retrieved from it).

index

Set to no if the value should not be indexed. Setting to no disables include_in_all. If set to no the field can be stored in _source, have include_in_all enabled, or store should be set to yes for this to be useful.

precision_step

The precision step (number of terms generated for each number value). Defaults to 4.

boost

The boost value. Defaults to 1.0.

null_value

When there is a (JSON) null value for the field, use the null_value as the field value. Defaults to not adding the field at all.

include_in_all

Should the field be included in the _all field (if enabled). If index is set to no this defaults to false, otherwise, defaults to true or to the parent object type setting.

ignore_malformed

Ignored a malformed number. Defaults to false. (Since @0.19.9).

Token Countedit

Note

Added in 0.90.8.

The token_count type maps to the JSON string type but indexes and stores the number of tokens in the string rather than the string itself. For example:

{
    "tweet" : {
        "properties" : {
            "message" : {
                "type" : "multi_field",
                "fields" : {
                    "name": {
                        "type": "string"
                    },
                    "word_count": {
                        "type" : "token_count",
                        "store" : "yes",
                        "analyzer" : "standard"
                    }
                }
            }
        }
    }
}

All the configuration that can be specified for a number can be specified for a token_count. The only extra configuration is the required analyzer field which specifies which analyzer to use to break the string into tokens. For best performance, use an analyzer with no token filters.

Note

Technically the token_count type sums position increments rather than counting tokens. This means that even if the analyzer filters out stop words they are included in the count.

Dateedit

The date type is a special type which maps to JSON string type. It follows a specific format that can be explicitly set. All dates are UTC. Internally, a date maps to a number type long, with the added parsing stage from string to long and from long to string. An example mapping:

{
    "tweet" : {
        "properties" : {
            "postDate" : {
                "type" : "date",
                "format" : "YYYY-MM-dd"
            }
        }
    }
}

The date type will also accept a long number representing UTC milliseconds since the epoch, regardless of the format it can handle.

The following table lists all the attributes that can be used with a date type:

Attribute Description

index_name

The name of the field that will be stored in the index. Defaults to the property/field name.

format

The date format. Defaults to dateOptionalTime.

store

Set to yes to store actual field in the index, no to not store it. Defaults to no (note, the JSON document itself is stored, and it can be retrieved from it).

index

Set to no if the value should not be indexed. Setting to no disables include_in_all. If set to no the field can be stored in _source, have include_in_all enabled, or store should be set to yes for this to be useful.

precision_step

The precision step (number of terms generated for each number value). Defaults to 4.

boost

The boost value. Defaults to 1.0.

null_value

When there is a (JSON) null value for the field, use the null_value as the field value. Defaults to not adding the field at all.

include_in_all

Should the field be included in the _all field (if enabled). If index is set to no this defaults to false, otherwise, defaults to true or to the parent object type setting.

ignore_malformed

Ignored a malformed number. Defaults to false. (Since @0.19.9).

Booleanedit

The boolean type Maps to the JSON boolean type. It ends up storing within the index either T or F, with automatic translation to true and false respectively.

{
    "tweet" : {
        "properties" : {
            "hes_my_special_tweet" : {
                "type" : "boolean",
            }
        }
    }
}

The boolean type also supports passing the value as a number (in this case 0 is false, all other values are true).

The following table lists all the attributes that can be used with the boolean type:

Attribute Description

index_name

The name of the field that will be stored in the index. Defaults to the property/field name.

store

Set to yes to store actual field in the index, no to not store it. Defaults to no (note, the JSON document itself is stored, and it can be retrieved from it).

index

Set to no if the value should not be indexed. Setting to no disables include_in_all. If set to no the field can be stored in _source, have include_in_all enabled, or store should be set to yes for this to be useful.

boost

The boost value. Defaults to 1.0.

null_value

When there is a (JSON) null value for the field, use the null_value as the field value. Defaults to not adding the field at all.

include_in_all

Should the field be included in the _all field (if enabled). If index is set to no this defaults to false, otherwise, defaults to true or to the parent object type setting.

Binaryedit

The binary type is a base64 representation of binary data that can be stored in the index. The field is stored by default and not indexed at all.

{
    "tweet" : {
        "properties" : {
            "image" : {
                "type" : "binary",
            }
        }
    }
}

The following table lists all the attributes that can be used with the binary type:

Attribute Description

index_name

The name of the field that will be stored in the index. Defaults to the property/field name.

Fielddata filtersedit

It is possible to control which field values are loaded into memory, which is particularly useful for faceting on string fields, using fielddata filters, which are explained in detail in the Fielddata section.

Fielddata filters can exclude terms which do not match a regex, or which don’t fall between a min and max frequency range:

{
    tweet: {
        type:      "string",
        analyzer:  "whitespace"
        fielddata: {
            filter: {
                regex: {
                    "pattern":        "^#.*"
                },
                frequency: {
                    min:              0.001,
                    max:              0.1,
                    min_segment_size: 500
                }
            }
        }
    }
}

These filters can be updated on an existing field mapping and will take effect the next time the fielddata for a segment is loaded. Use the Clear Cache API to reload the fielddata using the new filters.

Postings formatedit

Posting formats define how fields are written into the index and how fields are represented into memory. Posting formats can be defined per field via the postings_format option. Postings format are configurable since version 0.90.0.Beta1. Elasticsearch has several builtin formats:

direct
A postings format that uses disk-based storage but loads its terms and postings directly into memory. Note this postings format is very memory intensive and has certain limitation that don’t allow segments to grow beyond 2.1GB see {@link DirectPostingsFormat} for details.
memory
A postings format that stores its entire terms, postings, positions and payloads in a finite state transducer. This format should only be used for primary keys or with fields where each term is contained in a very low number of documents.
pulsing
A postings format in-lines the posting lists for very low frequent terms in the term dictionary. This is useful to improve lookup performance for low-frequent terms.
bloom_default
A postings format that uses a bloom filter to improve term lookup performance. This is useful for primarily keys or fields that are used as a delete key.
bloom_pulsing
A postings format that combines the advantages of bloom and pulsing to further improve lookup performance.
default
The default Elasticsearch postings format offering best general purpose performance. This format is used if no postings format is specified in the field mapping.
Postings format exampleedit

On all field types it possible to configure a postings_format attribute:

{
  "person" : {
     "properties" : {
         "second_person_id" : {"type" : "string", "postings_format" : "pulsing"}
     }
  }
}

On top of using the built-in posting formats it is possible define custom postings format. See codec module for more information.

Similarityedit

From version 0.90.Beta1 Elasticsearch includes changes from Lucene 4 that allows you to configure a similarity (scoring algorithm) per field. Allowing users a simpler extension beyond the usual TF/IDF algorithm. As part of this, new algorithms have been added including BM25. Also as part of the changes, it is now possible to define a Similarity per field, giving even greater control over scoring.

You can configure similarities via the similarity module

Configuring Similarity per Fieldedit

Defining the Similarity for a field is done via the similarity mapping property, as this example shows:

{
  "book" : {
    "properties" : {
      "title" : { "type" : "string", "similarity" : "BM25" }
    }
}

The following Similarities are configured out-of-box:

default
The Default TF/IDF algorithm used by Elasticsearch and Lucene in previous versions.
BM25
The BM25 algorithm. See Okapi_BM25 for more details.