How to use scripts
editHow to use scripts
editWherever scripting is supported in the Elasticsearch API, the syntax follows the same pattern:
The language the script is written in, which defaults to |
|
The script itself which may be specified as |
|
Any named parameters that should be passed into the script. |
For example, the following script is used in a search request to return a scripted field:
PUT my_index/_doc/1 { "my_field": 5 } GET my_index/_search { "script_fields": { "my_doubled_field": { "script": { "lang": "expression", "source": "doc['my_field'] * multiplier", "params": { "multiplier": 2 } } } } }
Script parameters
edit-
lang
-
Specifies the language the script is written in. Defaults to
painless
. -
source
,id
-
Specifies the source of the script. An
inline
script is specifiedsource
as in the example above. Astored
script is specifiedid
and is retrieved from the cluster state (see Stored Scripts). -
params
- Specifies any named parameters that are passed into the script as variables.
Prefer parameters
The first time Elasticsearch sees a new script, it compiles it and stores the compiled version in a cache. Compilation can be a heavy process.
If you need to pass variables into the script, you should pass them in as
named params
instead of hard-coding values into the script itself. For
example, if you want to be able to multiply a field value by different
multipliers, don’t hard-code the multiplier into the script:
"source": "doc['my_field'] * 2"
Instead, pass it in as a named parameter:
"source": "doc['my_field'] * multiplier", "params": { "multiplier": 2 }
The first version has to be recompiled every time the multiplier changes. The second version is only compiled once.
If you compile too many unique scripts within a small amount of time,
Elasticsearch will reject the new dynamic scripts with a
circuit_breaking_exception
error. By default, up to 15 inline scripts per
minute will be compiled. You can change this setting dynamically by setting
script.max_compilations_rate
.
Short script form
editA short script form can be used for brevity. In the short form, script
is represented
by a string instead of an object. This string contains the source of the script.
Short form:
"script": "ctx._source.likes++"
The same script in the normal form:
"script": { "source": "ctx._source.likes++" }
Stored scripts
editScripts may be stored in and retrieved from the cluster state using the
_scripts
end-point.
Request examples
editThe following are examples of using a stored script that lives at
/_scripts/{id}
.
First, create the script called calculate-score
in the cluster state:
POST _scripts/calculate-score { "script": { "lang": "painless", "source": "Math.log(_score * 2) + params.my_modifier" } }
You may also specify a context as part of the url path to compile a
stored script against that specific context in the form of
/_scripts/{id}/{context}
:
POST _scripts/calculate-score/score { "script": { "lang": "painless", "source": "Math.log(_score * 2) + params.my_modifier" } }
This same script can be retrieved with:
GET _scripts/calculate-score
Stored scripts can be used by specifying the id
parameters as follows:
GET twitter/_search { "query": { "script_score": { "query": { "match": { "message": "some message" } }, "script": { "id": "calculate-score", "params": { "my_modifier": 2 } } } } }
And deleted with:
DELETE _scripts/calculate-score
Search templates
editYou can also use the _scripts
API to store search templates. Search
templates save specific search requests with placeholder
values, called template parameters.
You can use stored search templates to run searches without writing out the entire query. Just provide the stored template’s ID and the template parameters. This is useful when you want to run a commonly used query quickly and without mistakes.
Search templates use the mustache templating language. See Search Template for more information and examples.
Script caching
editAll scripts are cached by default so that they only need to be recompiled
when updates occur. By default, scripts do not have a time-based expiration, but
you can change this behavior by using the script.cache.expire
setting.
You can configure the size of this cache by using the script.cache.max_size
setting.
By default, the cache size is 100
.
The size of scripts is limited to 65,535 bytes. This can be
changed by setting script.max_size_in_bytes
setting to increase that soft
limit, but if scripts are really large then a
native script engine should be considered.