Decay filter function for a no-limit value with ElasticSearch - boost

Question

I have the following documents (at least 1 000 000) in an ElasticSearch index:
{"title":"toto", "views":132, "likes":23, "date" : "2014-09-01..." ...}
Where title is indexed with a lang analyser, views and likes fields are integer from 0 to infinite, and the date is a ..date field.
I want to search by title, and boost documents if they are recent and have a high views and likes.
I am using a decay filter function for the date (from today as origin), it's working as expected, but I don't know how to do for boosting the views and likes fields, since I have no max-origin.
Here my search query:
POST /threads/_search
{
"query": {
"function_score": {
"query": {
"multi_match": {
"query": "air france",
"type": "phrase",
"fields": [
"title^4",
"desc"
]
}
},
"functions": [
{
"exp": {
"date": {
"origin": "2014/09/29 13:00:00",
"scale": "12h",
"offset":"6h",
"decay":0.5
}
}
}
]
}
}
}

Answer 1

You could try a "field_value_factor", as per this section in the documentation. And you'd need to test and assess the results, modify the "factor" and the boost you are giving to "title" and then test again and see if it's getting closer to what you need. Also, you can use search=explain to see how ES computes the _score. Something like this:
POST /threads/_search?explain
{
"query": {
"function_score": {
"query": {
"multi_match": {
"query": "air france",
"type": "phrase",
"fields": [
"title^8",
"desc"
]
}
},
"functions": [
{
"exp": {
"date": {
"origin": "2014/09/29 13:00:00",
"scale": "12h",
"offset":"6h",
"decay":0.5
}
}
},
{
"field_value_factor": {
"field": "views",
"modifier": "log2p",
"factor": 0.1
}
},
{
"field_value_factor": {
"field": "likes",
"modifier": "log2p",
"factor": 0.1
}
}
]
}
}
}