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_all
edit_all
editThe idea of the _all
field is that it includes the text of one or more
other fields within the document indexed. It can come very handy
especially for search requests, where we want to execute a search query
against the content of a document, without knowing which fields to
search on. This comes at the expense of CPU cycles and index size.
The _all
fields can be completely disabled. Explicit field mappings and
object mappings can be excluded / included in the _all
field. By
default, it is enabled and all fields are included in it for ease of
use.
When disabling the _all
field, it is a good practice to set
index.query.default_field
to a different value (for example, if you
have a main "message" field in your data, set it to message
).
One of the nice features of the _all
field is that it takes into
account specific fields boost levels. Meaning that if a title field is
boosted more than content, the title (part) in the _all
field will
mean more than the content (part) in the _all
field.
Here is a sample mapping:
{ "person" : { "_all" : {"enabled" : true}, "properties" : { "name" : { "type" : "object", "dynamic" : false, "properties" : { "first" : {"type" : "string", "store" : true , "include_in_all" : false}, "last" : {"type" : "string", "index" : "not_analyzed"} } }, "address" : { "type" : "object", "include_in_all" : false, "properties" : { "first" : { "properties" : { "location" : {"type" : "string", "store" : true, "index_name" : "firstLocation"} } }, "last" : { "properties" : { "location" : {"type" : "string"} } } } }, "simple1" : {"type" : "long", "include_in_all" : true}, "simple2" : {"type" : "long", "include_in_all" : false} } } }
The _all
fields allows for store
, term_vector
and analyzer
(with
specific index_analyzer
and search_analyzer
) to be set.
Highlighting
editFor any field to allow
highlighting it has
to be either stored or part of the _source
field. By default the _all
field does not qualify for either, so highlighting for it does not yield
any data.
Although it is possible to store
the _all
field, it is basically an
aggregation of all fields, which means more data will be stored, and
highlighting it might produce strange results.