ElasticSearch Date Field Statistics

Question

Inside my ElasticSearch index I have a type with a date field. I would like to get statistics for this field, such as which is the maximum and the minimum date, how many documents per month/year were published. I tried the following query:

  "query":{
       "match_all": {}
    }, 
   "facets":{
        "histo1":{
           "date_histogram":{
                "field":"published_date", 
                 "interval":"year"}
                 }
            }

but it returns me data that I do not know how to interpret:

  "facets" : {
"histo1" : {
  "_type" : "date_histogram",
  "entries" : [ {
    "time" : -946771200000,
    "count" : 23957
  }, {
    "time" : -915148800000,
    "count" : 45362
  }, {
    "time" : -883612800000,
    "count" : 34568
  }]
}

I would have expected to see the count for each year, the time value seems like a black box. Am I doing any mistake? I get the same when I try to use month.

Thank you very much!

Answer 1

From the Elasticsearch Reference for Date Histogram Facet:

By default, times are stored as UTC milliseconds since the epoch. Thus, all computation and "bucketing" / "rounding" is done on UTC. It is possible to provide a time zone (both pre rounding, and post rounding) value, which will cause all computations to take the relevant zone into account. The time returned for each bucket/entry is milliseconds since the epoch of the provided time zone.

You will need to convert the time facet values from their milliseconds since the epoch as a post search request operation to get them into a more preferred format.