[[search-aggregations-metrics-percentile-rank-aggregation]]
=== Percentile Ranks Aggregation

A `multi-value` metrics aggregation that calculates one or more percentile ranks
over numeric values extracted from the aggregated documents.  These values
can be extracted either from specific numeric fields in the documents, or
be generated by a provided script.

[NOTE]
==================================================
Please see <<search-aggregations-metrics-percentile-aggregation-approximation>> 
and <<search-aggregations-metrics-percentile-aggregation-compression>> for advice 
regarding approximation and memory use of the percentile ranks aggregation
==================================================

Percentile rank show the percentage of observed values which are below certain 
value.  For example, if a value is greater than or equal to 95% of the observed values
it is said to be at the 95th percentile rank.

Assume your data consists of website load times.  You may have a service agreement that 
95% of page loads completely within 15ms and 99% of page loads complete within 30ms.

Let's look at a range of percentiles representing load time:

[source,js]
--------------------------------------------------
{
    "aggs" : {
        "load_time_outlier" : {
            "percentile_ranks" : {
                "field" : "load_time", <1>
                "values" : [15, 30]
            }
        }
    }
}
--------------------------------------------------
<1> The field `load_time` must be a numeric field

The response will look like this:

[source,js]
--------------------------------------------------
{
    ...

   "aggregations": {
      "load_time_outlier": {
         "values" : {
            "15": 92,
            "30": 100
         }
      }
   }
}
--------------------------------------------------

From this information you can determine you are hitting the 99% load time target but not quite 
hitting the 95% load time target


==== Script

The percentile rank metric supports scripting.  For example, if our load times
are in milliseconds but we want to specify values in seconds, we could use
a script to convert them on-the-fly:

[source,js]
--------------------------------------------------
{
    "aggs" : {
        "load_time_outlier" : {
            "percentile_ranks" : {
                "values" : [3, 5],
                "script" : "doc['load_time'].value / timeUnit", <1>
                "params" : {
                    "timeUnit" : 1000   <2>
                }
            }
        }
    }
}
--------------------------------------------------
<1> The `field` parameter is replaced with a `script` parameter, which uses the
script to generate values which percentile ranks are calculated on
<2> Scripting supports parameterized input just like any other script
