[[query-dsl-script-score-query]] === Script Score Query experimental[] The `script_score` allows you to modify the score of documents that are retrieved by a query. This can be useful if, for example, a score function is computationally expensive and it is sufficient to compute the score on a filtered set of documents. To use `script_score`, you have to define a query and a script - a function to be used to compute a new score for each document returned by the query. For more information on scripting see <>. Here is an example of using `script_score` to assign each matched document a score equal to the number of likes divided by 10: [source,js] -------------------------------------------------- GET /_search { "query" : { "script_score" : { "query" : { "match": { "message": "elasticsearch" } }, "script" : { "source" : "doc['likes'].value / 10 " } } } } -------------------------------------------------- // CONSOLE // TEST[setup:twitter] ==== Accessing the score of a document within a script Within a script, you can {ref}/modules-scripting-fields.html#scripting-score[access] the `_score` variable which represents the current relevance score of a document. ==== Predefined functions within a Painless script You can use any of the available <> in the painless script. Besides these functions, there are a number of predefined functions that can help you with scoring. We suggest you to use them instead of rewriting equivalent functions of your own, as these functions try to be the most efficient by using the internal mechanisms. ===== saturation `saturation(value,k) = value/(k + value)` [source,js] -------------------------------------------------- "script" : { "source" : "saturation(doc['likes'].value, 1)" } -------------------------------------------------- // NOTCONSOLE ===== sigmoid `sigmoid(value, k, a) = value^a/ (k^a + value^a)` [source,js] -------------------------------------------------- "script" : { "source" : "sigmoid(doc['likes'].value, 2, 1)" } -------------------------------------------------- // NOTCONSOLE [[random-functions]] ===== Random functions There are two predefined ways to produce random values: `randomNotReproducible` and `randomReproducible`. `randomNotReproducible()` uses `java.util.Random` class to generate a random value of the type `long`. The generated values are not reproducible between requests' invocations. [source,js] -------------------------------------------------- "script" : { "source" : "randomNotReproducible()" } -------------------------------------------------- // NOTCONSOLE `randomReproducible(String seedValue, int seed)` produces reproducible random values of type `long`. This function requires more computational time and memory than the non-reproducible version. A good candidate for the `seedValue` is document field values that are unique across documents and already pre-calculated and preloaded in the memory. For example, values of the document's `_seq_no` field is a good candidate, as documents on the same shard have unique values for the `_seq_no` field. [source,js] -------------------------------------------------- "script" : { "source" : "randomReproducible(Long.toString(doc['_seq_no'].value), 100)" } -------------------------------------------------- // NOTCONSOLE A drawback of using `_seq_no` is that generated values change if documents are updated. Another drawback is not absolute uniqueness, as documents from different shards with the same sequence numbers generate the same random values. If you need random values to be distinct across different shards, you can use a field with unique values across shards, such as `_id`, but watch out for the memory usage as all these unique values need to be loaded into memory. [source,js] -------------------------------------------------- "script" : { "source" : "randomReproducible(doc['_id'].value, 100)" } -------------------------------------------------- // NOTCONSOLE [[decay-functions]] ===== Decay functions for numeric fields You can read more about decay functions {ref}/query-dsl-function-score-query.html#function-decay[here]. * `double decayNumericLinear(double origin, double scale, double offset, double decay, double docValue)` * `double decayNumericExp(double origin, double scale, double offset, double decay, double docValue)` * `double decayNumericGauss(double origin, double scale, double offset, double decay, double docValue)` [source,js] -------------------------------------------------- "script" : { "source" : "decayNumericLinear(params.origin, params.scale, params.offset, params.decay, doc['dval'].value)", "params": { <1> "origin": 20, "scale": 10, "decay" : 0.5, "offset" : 0 } } -------------------------------------------------- // NOTCONSOLE <1> Using `params` allows to compile the script only once, even if params change. ===== Decay functions for geo fields * `double decayGeoLinear(String originStr, String scaleStr, String offsetStr, double decay, GeoPoint docValue)` * `double decayGeoExp(String originStr, String scaleStr, String offsetStr, double decay, GeoPoint docValue)` * `double decayGeoGauss(String originStr, String scaleStr, String offsetStr, double decay, GeoPoint docValue)` [source,js] -------------------------------------------------- "script" : { "source" : "decayGeoExp(params.origin, params.scale, params.offset, params.decay, doc['location'].value)", "params": { "origin": "40, -70.12", "scale": "200km", "offset": "0km", "decay" : 0.2 } } -------------------------------------------------- // NOTCONSOLE ===== Decay functions for date fields * `double decayDateLinear(String originStr, String scaleStr, String offsetStr, double decay, JodaCompatibleZonedDateTime docValueDate)` * `double decayDateExp(String originStr, String scaleStr, String offsetStr, double decay, JodaCompatibleZonedDateTime docValueDate)` * `double decayDateGauss(String originStr, String scaleStr, String offsetStr, double decay, JodaCompatibleZonedDateTime docValueDate)` [source,js] -------------------------------------------------- "script" : { "source" : "decayDateGauss(params.origin, params.scale, params.offset, params.decay, doc['date'].value)", "params": { "origin": "2008-01-01T01:00:00Z", "scale": "1h", "offset" : "0", "decay" : 0.5 } } -------------------------------------------------- // NOTCONSOLE NOTE: Decay functions on dates are limited to dates in the default format and default time zone. Also calculations with `now` are not supported. ==== Faster alternatives Script Score Query calculates the score for every hit (matching document). There are faster alternative query types that can efficiently skip non-competitive hits: * If you want to boost documents on some static fields, use <>. ==== Transition from Function Score Query We are deprecating <>, and Script Score Query will be a substitute for it. Here we describe how Function Score Query's functions can be equivalently implemented in Script Score Query: ===== `script_score` What you used in `script_score` of the Function Score query, you can copy into the Script Score query. No changes here. ===== `weight` `weight` function can be implemented in the Script Score query through the following script: [source,js] -------------------------------------------------- "script" : { "source" : "params.weight * _score", "params": { "weight": 2 } } -------------------------------------------------- // NOTCONSOLE ===== `random_score` Use `randomReproducible` and `randomNotReproducible` functions as described in <>. ===== `field_value_factor` `field_value_factor` function can be easily implemented through script: [source,js] -------------------------------------------------- "script" : { "source" : "Math.log10(doc['field'].value * params.factor)", params" : { "factor" : 5 } } -------------------------------------------------- // NOTCONSOLE For checking if a document has a missing value, you can use `doc['field'].size() == 0`. For example, this script will use a value `1` if a document doesn't have a field `field`: [source,js] -------------------------------------------------- "script" : { "source" : "Math.log10((doc['field'].size() == 0 ? 1 : doc['field'].value()) * params.factor)", params" : { "factor" : 5 } } -------------------------------------------------- // NOTCONSOLE This table lists how `field_value_factor` modifiers can be implemented through a script: [cols="<,<",options="header",] |======================================================================= | Modifier | Implementation in Script Score | `none` | - | `log` | `Math.log10(doc['f'].value)` | `log1p` | `Math.log10(doc['f'].value + 1)` | `log2p` | `Math.log10(doc['f'].value + 2)` | `ln` | `Math.log(doc['f'].value)` | `ln1p` | `Math.log(doc['f'].value + 1)` | `ln2p` | `Math.log(doc['f'].value + 2)` | `square` | `Math.pow(doc['f'].value, 2)` | `sqrt` | `Math.sqrt(doc['f'].value)` | `reciprocal` | `1.0 / doc['f'].value` |======================================================================= ===== `decay functions` Script Score query has equivalent <> that can be used in script.