[[modules-scripting-using]]
== How to use scripts

Wherever scripting is supported in the Elasticsearch API, the syntax follows
the same pattern:

[source,js]
-------------------------------------
  "script": {
    "lang":   "...",  <1>
    "source" | "id": "...", <2>
    "params": { ... } <3>
  }
-------------------------------------
// NOTCONSOLE
<1> The language the script is written in, which defaults to `painless`.
<2> The script itself which may be specified as `source` for an inline script or `id` for a stored script.
<3> Any named parameters that should be passed into the script.

For example, the following script is used in a search request to return a
<<request-body-search-script-fields, scripted field>>:

[source,console]
-------------------------------------
PUT my-index-000001/_doc/1
{
  "my_field": 5
}

GET my-index-000001/_search
{
  "script_fields": {
    "my_doubled_field": {
      "script": {
        "lang":   "expression",
        "source": "doc['my_field'] * multiplier",
        "params": {
          "multiplier": 2
        }
      }
    }
  }
}
-------------------------------------

[discrete]
=== Script parameters

`lang`::

    Specifies the language the script is written in.  Defaults to `painless`.


`source`, `id`::

    Specifies the source of the script.  An `inline` script is specified
    `source` as in the example above. A `stored` script is specified `id`
    and is retrieved from the cluster state (see <<modules-scripting-stored-scripts,Stored Scripts>>).


`params`::

    Specifies any named parameters that are passed into the script as
    variables.

[IMPORTANT]
[[prefer-params]]
.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,js]
----------------------
  "source": "doc['my_field'] * 2"
----------------------
// NOTCONSOLE

Instead, pass it in as a named parameter:

[source,js]
----------------------
  "source": "doc['my_field'] * multiplier",
  "params": {
    "multiplier": 2
  }
----------------------
// NOTCONSOLE

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 75 scripts per
5 minutes will be compiled for most contexts and 375 scripts per 5 minutes
for `ingest` contexts. You can change these settings dynamically by setting
`script.context.$CONTEXT.max_compilations_rate` e.g.,
`script.context.field.max_compilations_rate=100/10m`.

========================================

[discrete]
[[modules-scripting-short-script-form]]
=== Short script form
A 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:

[source,js]
----------------------
  "script": "ctx._source.my-int++"
----------------------
// NOTCONSOLE

The same script in the normal form:

[source,js]
----------------------
  "script": {
    "source": "ctx._source.my-int++"
  }
----------------------
// NOTCONSOLE

[discrete]
[[modules-scripting-stored-scripts]]
=== Stored scripts

Scripts may be stored in and retrieved from the cluster state using the
`_scripts` end-point.

If the {es} {security-features} are enabled, you must have the following
privileges to create, retrieve, and delete stored scripts:

* cluster: `all` or `manage`

For more information, see <<security-privileges>>.


[discrete]
==== Request examples

The following are examples of using a stored script that lives at
`/_scripts/{id}`.

First, create the script called `calculate-score` in the cluster state:

[source,console]
-----------------------------------
POST _scripts/calculate-score
{
  "script": {
    "lang": "painless",
    "source": "Math.log(_score * 2) + params.my_modifier"
  }
}
-----------------------------------
// TEST[setup:my_index]

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}`:

[source,console]
-----------------------------------
POST _scripts/calculate-score/score
{
  "script": {
    "lang": "painless",
    "source": "Math.log(_score * 2) + params.my_modifier"
  }
}
-----------------------------------
// TEST[setup:my_index]

This same script can be retrieved with:

[source,console]
-----------------------------------
GET _scripts/calculate-score
-----------------------------------
// TEST[continued]

Stored scripts can be used by specifying the `id` parameters as follows:

[source,console]
--------------------------------------------------
GET my-index-000001/_search
{
  "query": {
    "script_score": {
      "query": {
        "match": {
            "message": "some message"
        }
      },
      "script": {
        "id": "calculate-score",
        "params": {
          "my_modifier": 2
        }
      }
    }
  }
}
--------------------------------------------------
// TEST[continued]

And deleted with:

[source,console]
-----------------------------------
DELETE _scripts/calculate-score
-----------------------------------
// TEST[continued]

[discrete]
[[modules-scripting-search-templates]]
=== Search templates
You can also use the `_scripts` API to store **search templates**. Search
templates save specific <<search-search,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 https://mustache.github.io/mustache.5.html[mustache
templating language]. See <<search-template>> for more information and examples.

[discrete]
[[modules-scripting-using-caching]]
=== Script caching

All 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 configure the size of this cache using the
`script.context.$CONTEXT.cache_expire` setting.
By default, the cache size is `100` for all contexts except the `ingest` and the
`processor_conditional` context, where it is `200`.

|====
| Context | Default Cache Size
| `ingest`  | 200
| `processor_conditional` | 200
| default | 100
|====

NOTE: 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
<<modules-scripting-engine,native script engine>> should be considered.

[[scripts-and-search-speed]]
=== Scripts and search speed

Scripts can't make use of {es}'s index structures or related optimizations. This
can sometimes result in slower search speeds.

If you often use scripts to transform indexed data, you can speed up search by
making these changes during ingest instead. However, that often means slower
index speeds.

.*Example*
[%collapsible]
=====
An index, `my_test_scores`, contains two `long` fields:

* `math_score`
* `verbal_score`

When running searches, users often use a script to sort results by the sum of
these two field's values.

[source,console]
----
GET /my_test_scores/_search
{
  "query": {
    "term": {
      "grad_year": "2099"
    }
  },
  "sort": [
    {
      "_script": {
        "type": "number",
        "script": {
          "source": "doc['math_score'].value + doc['verbal_score'].value"
        },
        "order": "desc"
      }
    }
  ]
}
----
// TEST[s/^/PUT my_test_scores\n/]

To speed up search, you can perform this calculation during ingest and index the
sum to a field instead.

First, <<indices-put-mapping,add a new field>>, `total_score`, to the index. The
`total_score` field will contain sum of the `math_score` and `verbal_score`
field values.

[source,console]
----
PUT /my_test_scores/_mapping
{
  "properties": {
    "total_score": {
      "type": "long"
    }
  }
}
----
// TEST[continued]

Next, use an <<ingest,ingest pipeline>> containing the
<<script-processor,`script`>> processor to calculate the sum of `math_score` and
`verbal_score` and index it in the `total_score` field.

[source,console]
----
PUT _ingest/pipeline/my_test_scores_pipeline
{
  "description": "Calculates the total test score",
  "processors": [
    {
      "script": {
        "source": "ctx.total_score = (ctx.math_score + ctx.verbal_score)"
      }
    }
  ]
}
----
// TEST[continued]

To update existing data, use this pipeline to <<docs-reindex,reindex>> any
documents from `my_test_scores` to a new index, `my_test_scores_2`.

[source,console]
----
POST /_reindex
{
  "source": {
    "index": "my_test_scores"
  },
  "dest": {
    "index": "my_test_scores_2",
    "pipeline": "my_test_scores_pipeline"
  }
}
----
// TEST[continued]

Continue using the pipeline to index any new documents to `my_test_scores_2`.

[source,console]
----
POST /my_test_scores_2/_doc/?pipeline=my_test_scores_pipeline
{
  "student": "kimchy",
  "grad_year": "2099",
  "math_score": 800,
  "verbal_score": 800
}
----
// TEST[continued]

These changes may slow indexing but allow for faster searches. Users can now
sort searches made on `my_test_scores_2` using the `total_score` field instead
of using a script.

[source,console]
----
GET /my_test_scores_2/_search
{
  "query": {
    "term": {
      "grad_year": "2099"
    }
  },
  "sort": [
    {
      "total_score": {
        "order": "desc"
      }
    }
  ]
}
----
// TEST[continued]

////
[source,console]
----
DELETE /_ingest/pipeline/my_test_scores_pipeline
----
// TEST[continued]

[source,console-result]
----
{
"acknowledged": true
}
----
////
=====

We recommend testing and benchmarking any indexing changes before deploying them
in production.

[discrete]
[[modules-scripting-errors]]
=== Script errors
Elasticsearch returns error details when there is a compliation or runtime
exception.  The contents of this response are useful for tracking down the
problem.

experimental[]

The contents of `position` are experimental and subject to change.
