ESQL: Add decay function #121526
Description
We already support the following decay functions in painless for the script_score query:
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)
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)
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)
Decay functions are used to penalize scores based on recency (for date types) or distance (numeric and geo types) and this is a useful feature we want to add to ES|QL.
We do not want to add 9 different decay functions.
We will have one decay function, that default to linear decay:
decay(value, origin, scale) // defaults to linear
decay(value, origin, scale, { "offset": 0.5 , "decay": 0, "type": "exp"}) // use a different type
For parameters:
Value: numeric, spatial, date types - required
Origin: numeric, spatial, date types - required
Scale: numeric, spatial, date types - required
Options:
Offset: numeric, spatial, date types - defaults to 0.5 (same as https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-function-score-query#function-decay)
Decay: numeric - default to 0 (same as https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-function-score-query#function-decay)
Type: can be "linear" (default), "exp" or `"gauss"
The return type should be double.
How to apply score decay
It should be as simple as:
FROM index METADATA _score
| ....
| EVAL final_score = _score - decay(value, origin, scale)