Datetime now

Serverless Stack

Under most Painless contexts the current datetime, now, is not supported. There are two primary reasons for this. The first is that scripts are often run once per document, so each time the script is run a different now is returned. The second is that scripts are often run in a distributed fashion without a way to appropriately synchronize now. Instead, pass in a user-defined parameter with either a string datetime or numeric datetime for now. A numeric datetime is preferred as there is no need to parse it for comparison.

• Use a numeric datetime as now

  • Assumptions:

    • The field input_datetime exists in all indexes as part of the query
    • All indexed documents contain the field input_datetime

  • Mappings:

    {
      "mappings": {
          ...
          "properties": {
            ...
            "input_datetime": {
            "type": "date"
          }
          ...
        }
        ...
      }
    }
    		

  • Input:

    ...
    "script": {
        ...
        "params": {
            "now": <generated numeric datetime in milliseconds since epoch>
        }
    }
    ...
    		

  • Script:

    long now = params['now'];
    ZonedDateTime inputDateTime = doc['input_datetime'];
    long millisDateTime = inputDateTime.toInstant().toEpochMilli();
    long elapsedTime = now - millisDateTime;
    		

• Use a string datetime as now

  • Assumptions:

    • The field input_datetime exists in all indexes as part of the query
    • All indexed documents contain the field input_datetime

  • Mappings:

    {
      "mappings": {
        ...
        "properties": {
          ...
          "input_datetime": {
            "type": "date"
          }
          ...
        }
        ...
      }
    }
    		

  • Input:

    ...
    "script": {
        ...
        "params": {
            "now": "<generated string datetime in ISO-8601>"
        }
    }
    ...
    		

  • Script:

    String nowString = params['now'];
    ZonedDateTime nowZdt = ZonedDateTime.parse(nowString);
    long now = ZonedDateTime.toInstant().toEpochMilli();
    ZonedDateTime inputDateTime = doc['input_datetime'];
    long millisDateTime = zdt.toInstant().toEpochMilli();
    long elapsedTime = now - millisDateTime;
    		

    1. This parses the same string datetime every time the script runs. Use a numeric datetime to avoid a significant performance hit.