289 lines
11 KiB
Plaintext
289 lines
11 KiB
Plaintext
[[modules-scripting]]
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== Scripting
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The scripting module allows to use scripts in order to evaluate custom
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expressions. For example, scripts can be used to return "script fields"
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as part of a search request, or can be used to evaluate a custom score
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for a query and so on.
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The scripting module uses by default http://mvel.codehaus.org/[mvel] as
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the scripting language with some extensions. mvel is used since it is
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extremely fast and very simple to use, and in most cases, simple
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expressions are needed (for example, mathematical equations).
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Additional `lang` plugins are provided to allow to execute scripts in
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different languages. Currently supported plugins are `lang-javascript`
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for JavaScript, `lang-groovy` for Groovy, and `lang-python` for Python.
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All places where a `script` parameter can be used, a `lang` parameter
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(on the same level) can be provided to define the language of the
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script. The `lang` options are `mvel`, `js`, `groovy`, `python`, and
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`native`.
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[float]
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=== Default Scripting Language
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The default scripting language (assuming no `lang` parameter is
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provided) is `mvel`. In order to change it set the `script.default_lang`
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to the appropriate language.
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[float]
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=== Preloaded Scripts
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Scripts can always be provided as part of the relevant API, but they can
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also be preloaded by placing them under `config/scripts` and then
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referencing them by the script name (instead of providing the full
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script). This helps reduce the amount of data passed between the client
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and the nodes.
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The name of the script is derived from the hierarchy of directories it
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exists under, and the file name without the lang extension. For example,
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a script placed under `config/scripts/group1/group2/test.py` will be
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named `group1_group2_test`.
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[float]
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=== Disabling dynamic scripts
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We recommend running Elasticsearch behind an application or proxy,
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which protects Elasticsearch from the outside world. If users are
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allowed to run dynamic scripts (even in a search request), then they
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have the same access to your box as the user that Elasticsearch is
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running as.
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First, you should not run Elasticsearch as the `root` user, as this
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would allow a script to access or do *anything* on your server, without
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limitations. Second, you should not expose Elasticsearch directly to
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users, but instead have a proxy application inbetween. If you *do*
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intend to expose Elasticsearch directly to your users, then you have
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to decide whether you trust them enough to run scripts on your box or
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not. If not, then even if you have a proxy which only allows `GET`
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requests, you should disable dynamic scripting by adding the following
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setting to the `config/elasticsearch.yml` file on every node:
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[source,yaml]
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-----------------------------------
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script.disable_dynamic: true
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-----------------------------------
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This will still allow execution of named scripts provided in the config, or
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_native_ Java scripts registered through plugins, however it will prevent
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users from running arbitrary scripts via the API.
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[float]
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=== Automatic Script Reloading
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added[0.90.6]
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The `config/scripts` directory is scanned periodically for changes.
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New and changed scripts are reloaded and deleted script are removed
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from preloaded scripts cache. The reload frequency can be specified
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using `watcher.interval` setting, which defaults to `60s`.
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To disable script reloading completely set `script.auto_reload_enabled`
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to `false`.
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[float]
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=== Native (Java) Scripts
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Even though `mvel` is pretty fast, allow to register native Java based
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scripts for faster execution.
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In order to allow for scripts, the `NativeScriptFactory` needs to be
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implemented that constructs the script that will be executed. There are
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two main types, one that extends `AbstractExecutableScript` and one that
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extends `AbstractSearchScript` (probably the one most users will extend,
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with additional helper classes in `AbstractLongSearchScript`,
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`AbstractDoubleSearchScript`, and `AbstractFloatSearchScript`).
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Registering them can either be done by settings, for example:
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`script.native.my.type` set to `sample.MyNativeScriptFactory` will
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register a script named `my`. Another option is in a plugin, access
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`ScriptModule` and call `registerScript` on it.
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Executing the script is done by specifying the `lang` as `native`, and
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the name of the script as the `script`.
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Note, the scripts need to be in the classpath of elasticsearch. One
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simple way to do it is to create a directory under plugins (choose a
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descriptive name), and place the jar / classes files there, they will be
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automatically loaded.
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[float]
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=== Score
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In all scripts that can be used in facets, allow to access the current
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doc score using `doc.score`.
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[float]
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=== Document Fields
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Most scripting revolve around the use of specific document fields data.
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The `doc['field_name']` can be used to access specific field data within
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a document (the document in question is usually derived by the context
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the script is used). Document fields are very fast to access since they
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end up being loaded into memory (all the relevant field values/tokens
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are loaded to memory).
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The following data can be extracted from a field:
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[cols="<,<",options="header",]
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|=======================================================================
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|Expression |Description
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|`doc['field_name'].value` |The native value of the field. For example,
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if its a short type, it will be short.
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|`doc['field_name'].values` |The native array values of the field. For
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example, if its a short type, it will be short[]. Remember, a field can
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have several values within a single doc. Returns an empty array if the
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field has no values.
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|`doc['field_name'].empty` |A boolean indicating if the field has no
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values within the doc.
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|`doc['field_name'].multiValued` |A boolean indicating that the field
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has several values within the corpus.
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|`doc['field_name'].lat` |The latitude of a geo point type.
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|`doc['field_name'].lon` |The longitude of a geo point type.
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|`doc['field_name'].lats` |The latitudes of a geo point type.
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|`doc['field_name'].lons` |The longitudes of a geo point type.
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|`doc['field_name'].distance(lat, lon)` |The `plane` distance (in miles)
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of this geo point field from the provided lat/lon.
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|`doc['field_name'].arcDistance(lat, lon)` |The `arc` distance (in
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miles) of this geo point field from the provided lat/lon.
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|`doc['field_name'].distanceInKm(lat, lon)` |The `plane` distance (in
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km) of this geo point field from the provided lat/lon.
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|`doc['field_name'].arcDistanceInKm(lat, lon)` |The `arc` distance (in
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km) of this geo point field from the provided lat/lon.
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|`doc['field_name'].geohashDistance(geohash)` |The distance (in miles)
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of this geo point field from the provided geohash.
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|`doc['field_name'].geohashDistanceInKm(geohash)` |The distance (in km)
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of this geo point field from the provided geohash.
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|=======================================================================
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[float]
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=== Stored Fields
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Stored fields can also be accessed when executed a script. Note, they
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are much slower to access compared with document fields, but are not
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loaded into memory. They can be simply accessed using
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`_fields['my_field_name'].value` or `_fields['my_field_name'].values`.
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[float]
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=== Source Field
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The source field can also be accessed when executing a script. The
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source field is loaded per doc, parsed, and then provided to the script
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for evaluation. The `_source` forms the context under which the source
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field can be accessed, for example `_source.obj2.obj1.field3`.
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Accessing `_source` is much slower compared to using `_doc`
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but the data is not loaded into memory. For a single field access `_fields` may be
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faster than using `_source` due to the extra overhead of potentially parsing large documents.
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However, `_source` may be faster if you access multiple fields or if the source has already been
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loaded for other purposes.
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[float]
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=== mvel Built In Functions
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There are several built in functions that can be used within scripts.
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They include:
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[cols="<,<",options="header",]
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|=======================================================================
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|Function |Description
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|`time()` |The current time in milliseconds.
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|`sin(a)` |Returns the trigonometric sine of an angle.
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|`cos(a)` |Returns the trigonometric cosine of an angle.
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|`tan(a)` |Returns the trigonometric tangent of an angle.
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|`asin(a)` |Returns the arc sine of a value.
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|`acos(a)` |Returns the arc cosine of a value.
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|`atan(a)` |Returns the arc tangent of a value.
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|`toRadians(angdeg)` |Converts an angle measured in degrees to an
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approximately equivalent angle measured in radians
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|`toDegrees(angrad)` |Converts an angle measured in radians to an
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approximately equivalent angle measured in degrees.
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|`exp(a)` |Returns Euler's number _e_ raised to the power of value.
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|`log(a)` |Returns the natural logarithm (base _e_) of a value.
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|`log10(a)` |Returns the base 10 logarithm of a value.
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|`sqrt(a)` |Returns the correctly rounded positive square root of a
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value.
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|`cbrt(a)` |Returns the cube root of a double value.
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|`IEEEremainder(f1, f2)` |Computes the remainder operation on two
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arguments as prescribed by the IEEE 754 standard.
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|`ceil(a)` |Returns the smallest (closest to negative infinity) value
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that is greater than or equal to the argument and is equal to a
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mathematical integer.
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|`floor(a)` |Returns the largest (closest to positive infinity) value
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that is less than or equal to the argument and is equal to a
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mathematical integer.
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|`rint(a)` |Returns the value that is closest in value to the argument
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and is equal to a mathematical integer.
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|`atan2(y, x)` |Returns the angle _theta_ from the conversion of
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rectangular coordinates (_x_, _y_) to polar coordinates (r,_theta_).
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|`pow(a, b)` |Returns the value of the first argument raised to the
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power of the second argument.
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|`round(a)` |Returns the closest _int_ to the argument.
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|`random()` |Returns a random _double_ value.
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|`abs(a)` |Returns the absolute value of a value.
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|`max(a, b)` |Returns the greater of two values.
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|`min(a, b)` |Returns the smaller of two values.
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|`ulp(d)` |Returns the size of an ulp of the argument.
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|`signum(d)` |Returns the signum function of the argument.
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|`sinh(x)` |Returns the hyperbolic sine of a value.
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|`cosh(x)` |Returns the hyperbolic cosine of a value.
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|`tanh(x)` |Returns the hyperbolic tangent of a value.
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|`hypot(x, y)` |Returns sqrt(_x2_ + _y2_) without intermediate overflow
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or underflow.
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|=======================================================================
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[float]
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=== Arithmetic precision in MVEL
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When dividing two numbers using MVEL based scripts, the engine tries to
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be smart and adheres to the default behaviour of java. This means if you
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divide two integers (you might have configured the fields as integer in
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the mapping), the result will also be an integer. This means, if a
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calculation like `1/num` is happening in your scripts and `num` is an
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integer with the value of `8`, the result is `0` even though you were
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expecting it to be `0.125`. You may need to enforce precision by
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explicitly using a double like `1.0/num` in order to get the expected
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result.
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